Abstract
There is substantial evidence supporting the role of certain oral bacteria species in the onset and progression of periodontitis. Nevertheless, results of independent-culture diagnostic methods introduced about a decade ago have pointed to the existence of new periodontal pathogens. However, the data of these studies have not been evaluated together, which may generate some misunderstanding on the actual role of these microorganisms in the etiology of periodontitis. The aim of this systematic review was to determine the current weight of evidence for newly identified periodontal pathogens based on the results of “association” studies. This review was conducted and reported in accordance with the PRISMA statement. The MEDLINE, EMBASE, and Cochrane databases were searched up to September 2013 for studies (1) comparing microbial data of subgingival plaque samples collected from subjects with periodontitis and periodontal health and (2) evaluating at least 1 microorganism other than the already-known periodontal pathogens. From 1,450 papers identified, 41 studies were eligible. The data were extracted and registered in predefined piloted forms. The results suggested that there is moderate evidence in the literature to support the association of 17 species or phylotypes from the phyla Bacteroidetes, Candidatus Saccharibacteria, Firmicutes, Proteobacteria, Spirochaetes, and Synergistetes. The phylum Candidatus Saccharibacteria and the Archaea domain also seem to have an association with disease. These data point out the importance of previously unidentified species in the etiology of periodontitis and might guide future investigations on the actual role of these suspected new pathogens in the onset and progression of this infection.
Keywords: Archaea, Bacteria, dental plaque, microbiology, periodontal disease, DNA
Introduction
Periodontitis is an infectious disease involving a complex interaction between the oral microorganisms organized in a biofilm structure and the host immune response. Its clinical consequence is the destruction of the tissues that support and protect the tooth. As with any other infection, identification of the microbial pathogens associated with the etiology of periodontitis is the first step toward the development of effective therapeutic approaches. The establishment of a microorganism as a true pathogen should be based on 2 main levels of evidence: (1) the organism should be present in higher prevalence and/or levels in disease than in health (“association” studies), and (2) its suppression or elimination should reduce or stop disease progression (“elimination” studies; Socransky, 1979).
The composition of the oral microbiota—specifically, the subgingival microbiota—has been studied for over a century. Unfortunately, for many decades, research in this field was considerably delayed due to technical difficulties, such as the need to identify microorganisms to the species level using only culture techniques. The use of immunologic and molecular diagnostic tests for the identification of microorganisms independent on cultivation—such as DNA probes, polymerase chain reaction, and immunoassays—began in the 1990s and allowed a great progress in the understanding about the composition of the subgingival microbiota. Using one of these molecular tests—namely, checkerboard DNA-DNA hybridization—Socransky et al. (1998) described the role of 5 main microbial complexes in the subgingival biofilm. Some species/complexes were associated with periodontal health, such as the yellow (Streptococcus species) and purple (Veillonela parvula and Actinomyces odontolyticus) complexes, while others were closely associated with disease, such as the red (Porphyromonas gingivalis, Treponema denticola, Tannerella forsythia) and orange complexes (Fusobacterium, Prevotella, and Campylobacter species). Afterward, other association and elimination studies have confirmed the involvement of the 3 members of the red complex and some members of the orange complex, such as Prevotella intermedia, Parvimonas micra, Fusobacterium nucleatum, Eubacterium nodatum, and Aggregatibacter actinomycetemcomitans, with the etiology of different periodontal conditions (Teles et al., 2013).
In 2001, using cloning and Sanger sequencing, Paster et al. suggested a possible role of cultivable and not-yet-cultivable/unrecognized microbial species in the etiology of periodontitis, confirming the idea that the diversity of the oral microbiota was more complex than previously known. Subsequently, a number of other studies using several molecular approaches, including next-generation sequencing techniques, were published in the periodontal literature (Kumar et al., 2005; Matarazzo et al., 2011; Teles et al., 2011; Griffen et al., 2012; Abusleme et al., 2013). The overall data provided by these studies for more than 12 yr suggested the existence of new periodontal pathogens. However, studies are diverse in terms of the diagnostic test used, the taxa assessed, and the number of samples evaluated, which may generate some misunderstanding while trying to draw objective conclusions on the actual role of these microorganisms in the etiology of periodontitis. Thus, a thorough review compiling the results of these studies could be helpful for the accurate interpretation of the present literature on this topic. Therefore, the aim of this systematic review was to determine the current weight of evidence for newly identified periodontal pathogens based on the results of association studies.
Materials & Methods
This systematic review was conducted in accordance with the recommendations of PRISMA statement (i.e., Preferred Reporting Items for Systematic Reviews and Meta-analysis; Moher et al., 2009).
Focused Question
What is the weight of evidence for the existence of newly identified periodontal pathogens based on association studies?
Inclusion Criteria
The manuscripts meeting the following criteria were included:
Studies of any design that compared microbial data of subgingival plaque samples collected from systemically healthy patients with periodontitis and periodontal health
Studies evaluating at least 1 new microorganism other than the species already suggested as periodontal pathogens or putative periodontal pathogens (P. gingivalis, T. denticola, T. forsythia, F. nucleatum, Fusobacterium periodonticum, P. intermedia, Prevotella nigrescens, P. micra, Campylobacter gracilis, Campylobacter rectus, Campylobacter showae, E. nodatum, Streptococcus constellatus and A. actinomycetemcomitans; “Proceedings of the World Workshop,” 1996; Socransky et al., 1998; Teles et al., 2013)
Exclusion Criteria
Studies published in languages other than English, Spanish, French, or Portuguese
Lack of baseline data
Lack of a direct comparison of baseline microbial data between periodontitis and periodontally healthy groups
Lack of data from subgingival plaque samples in periodontitis and/or periodontally healthy groups
Lack of data from subgingival plaque samples of systemically healthy subjects
Studies that evaluated only subjects with localized aggressive periodontitis or refractory periodontitis
Review studies
Studies that evaluated only viruses
Search Strategy and Data Extraction
The MEDLINE (via PubMed), EMBASE, and Cochrane Library databases were searched up to September 10, 2013, by 2 independent reviewers (P.J.P.C. and P.D.) using the search strategy described in Appendix Table 1. In addition, a manual search was conducted based on the reference list of the selected manuscripts and review articles. The studies were screened independently by 2 researchers (E.L., M.Fa.), and any disagreement was solved through discussion. When disagreement persisted, another researcher was consulted to achieve consensus (M.Fe.). Those studies that fulfilled the inclusion and exclusion criteria were processed for data extraction, conducted by another 2 independent researchers (P.J.P.C. and C.G.). The following information was collected from each manuscript and registered in predefined piloted forms:
Study location
Type of trial
Characteristics of participants (e.g., systemically health status, number of patients per group, age, periodontal condition)
Type of microbiological evaluation (e.g., individually or pooled strategy, number of samples evaluated, employed diagnostic method)
Microbiological outcomes (e.g., microorganisms appraised [e.g., Bacteria and/or Archaea], taxa in higher levels and/or proportion and/or abundance and/or prevalence in periodontitis than in periodontal health or those reported by the authors as being associated with periodontitis [primary outcome of interest])
Conflict of interest
Source of funding
To accurately assign the most updated names to the microorganisms so that we could avoid taxa repetition and to assign a Human Oral Taxon (HOT) number whenever available, the Human Oral Microbiome Database (HOMD, http://www.homd.org/index.php, October 28, 2013) was interrogated for each microorganism cited on the 41 included studies by 3 researchers (P.J.P.C., L.C.F., N.T.). For this step, we used the nomenclature given by each author (i.e., the microorganism/strain/isolate name or the Genbank accession number). When this query did not return any result, the local HOMD blast tool was used to query the available 16S rDNA sequence with length >1,300 nt. In cases in which both queries were unsuccessful, the author’s nomenclature was retained. Phyla, class, species, and phylotypes were indexed according to the National Center for Biotechnology Information taxonomy browser (http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi, October 29, 2013) when available; otherwise, HOMD classification was retained.
Results
Studies Included
A total of 1,450 titles were found during the electronic search. After title screening, 1,303 studies were excluded, and 147 were selected. After abstract reading, 116 studies were excluded, and 31 full-text publications were comprehensively evaluated. In addition, 15 studies were selected during the manual search. After reading these 46 studies, 5 were excluded for not meeting the inclusion criteria (Appendix Table 2). Therefore, 41 studies were included in this study (Figure).
Figure.
Flowchart of the search strategy.
Study Designs: Periodontal Conditions/Samples Evaluated and Diagnostic Techniques Used
Table 1 presents the studies included and their main methodological features. The majority of the studies had more patients and samples in the periodontitis than in the periodontally healthy group. A total of 912 individuals with periodontal health and 1,918 with periodontitis were evaluated. Subgingival biofilm samples were processed individually in 24 studies and pooled in 13 studies. One study used both sampling methods (Liu et al., 2012); 2 studies did not provide information about the number of samples collected (Dewhirst et al., 2000; Paster et al., 2001); and 1 study (Bringuier et al., 2013) did not clarify whether the samples were analyzed individually or pooled. A total of 3,508 and 10,800 subgingival plaque samples were evaluated from subjects with periodontal health or periodontitis, respectively.
Table 1.
Summary of the Methodological Features of the Included Studies
| Subjects, n |
Samples, n |
||||||
|---|---|---|---|---|---|---|---|
| H | GAgP | ChP | RP | H | P | Method/Taxa Evaluated | |
| Willis et al., 1999 | 10 | 21 | 10 (I) | 21 (I) | Nested PCR. 7 Treponema species | ||
| Harper-Owen et al., 1999 | 20 | 28 | 40 (I) | 56 (I) | PCR/Sanger sequencing. Phylotype PUS3.422, PUS9.170, PUS9.180 | ||
| Dewhirst et al., 2000 | 2 | 1 | 8 | NA | NA | PCR/cloning/Sanger sequencing. Spirochaetes phylum | |
| Sawada et al., 2000 | 20 | 40 | 20 (I) | 40 (I) | PCR. Selenomonas sputigena, Centipeda periodontii | ||
| Macuch and Tanner, 2000 | 18 | 52 | 44 (I) | 52 (I) | Culture and SDS-Page. Campylobacter species | ||
| Paster et al., 2001 | 5 | 9 | 11 | NA | NA | PCR/cloning/Sanger sequencing. Bacteria domain and Spirochaetes, Bacteroidetes phyla | |
| Colombo et al., 2002 | 14 | 25 | 1,492 (I) | 2,540 (I) | Checkerboard DNA-DNA hybridization. 42 bacterial species | ||
| Leys et al., 2002 | 172 | 121 | 172 (P) | 121 (P) | Nested PCR/Sanger sequencing. Bacteroides forsythus and oral clone BU063 | ||
| Asai et al., 2002 | 13 | 37 | 13 (P) | 37 (P) | PCR and qPCR. Total Treponemes, T.denticola, T. medium, and T. vincentii | ||
| Hutter et al., 2003 | 6 | 26 | 6 (I) | 26 (I) | PCR/cloning/Sanger sequencing. Bacteria domain | ||
| Brinig et al., 2003 | 4 | 42 | 18 (I) | 53 (I) | PCR/cloning/Sanger sequencing, qPCR and FISH. Candidate division TM7 (Phylum Candidatus Saccharibacteria) and TM7 I025 subgroup | ||
| Ouverney et al., 2003 | 4 | 12 | 9 (I) | 12 (I) | FISH. Candidate division TM7 (Phylum Candidatus Saccharibacteria) and TM7 I025 subgroup | ||
| Kumar et al., 2003 | 66 | 66 | 66 (P) | 66 (P) | Nested PCR and Sanger sequencing. 39 bacterial species or phylotypes | ||
| Zijnge et al., 2003 | 6 | 9 | 6 (P) | 9 (P) | PCR/DGGE and DGGE/PCR/Sanger sequencing. Bacteria domain | ||
| Booth et al., 2004 | 40 | 40 | 40 (P) | 80 (P) | Slot-blot hybridization. Bulleidia extructa, Eubacterium nodatum, Mogibacterium timidum, and Slackia exigua | ||
| Murdoch et al., 2004 | 28 | 28 | 84 (I) | 168 (I) | Culture. Oral staphylococci | ||
| Lepp et al., 2004 | 8 | 50 | 29 (I) | 205 (I) | PCR/cloning/Sanger sequencing, FISH and qPCR. Archaea and Bacteria domains | ||
| Mayanagi et al., 2004 | 12 | 18 | 12 (I) | 18 (I) | Nested PCR. 25 putative or probable periodontal pathogens | ||
| Kumar et al., 2005 | 15 | 15 | 15 (P) | 30 (P) | PCR/cloning/Sanger sequencing. Bacteria domain | ||
| Li et al., 2006 | 20 | 35 | 20 (P) | 35 (P) | PCR/Sanger sequencing. Phylotype AU 126 and X 112 | ||
| Souto et al., 2006 | 3 | 14 | 200 (I) | 400 (I) | Checkerboard DNA-DNA hybridization. 11 putative periopathogen bacteria | ||
| Ledder et al., 2007 | 18 | 29 | 18 (I) | 29 (I) | PCR/DGGE, DGGE/PCR/Sanger sequencing for Bacteria and Multiplex PCR for Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, Tannerella forsythensis | ||
| Souto and Colombo, 2008 | 56 | 169 | 56 (P) | 169 (P) | PCR. Enterococcus faecalis | ||
| Vianna et al., 2008 | 65 | 102 | 65 (P) | 102 (P) | qPCR and Sanger sequencing. Hydrogenotrophic Archaea and Bacteria | ||
| Li et al., 2009 | 15 | 41 | 15 (P) | 41 (P) | PCR and PCR/cloning/Sanger sequencing. Archaea domain | ||
| Riep et al., 2009 | 21 | 44 | 46 | 105 (I) | 450 (I) | Dot blot hybridization. 10 Putative periodontal pathogen bacteria | |
| Vartoukian et al., 2009 | 5 | 5 | 5 (P) | 10 (P) | PCR/cloning/Sanger sequencing and FISH. Synergistetes phylum | ||
| Schlafer et al., 2010* | 19 | 72 | 30 | 82 (I) | 408 (I) | Dot blot hybridization. Filifactor alocis, red complex, A.actinomycetemcomitans, Fusobacterium nucleatum, Prevotella intermedia | |
| Abiko et al., 2010 | 12 | 28 | 12 (I) | 28 (I) | qPCR. Total Bacteria and 13 bacterial species | ||
| Drescher et al., 2010* | 19 | 62 | 82 | 82 (I) | 660 (I) | Dot blot hybridization. Selenomonas genus, Centipeda genus | |
| da Silva-Boghossian et al., 2011 | 51 | 90 | 219 | 357 (I) | 4,326 (I) | Checkerboard DNA-DNA hybridization. Red Complex, A. actinomycetemcomitans, Acinetobacter baumannii, Escherichia coli, E. faecalis, Pseudomonas aeruginosa, Staphylococcus aureus | |
| Matarazzo et al., 2011 | 30 | 30 | 60 (I) | 103 (I) | qPCR and PCR/cloning/Sanger sequencing. Bacteria and Archaea domains | ||
| Teles et al., 2011 | 8 | 11 | 112 (I) | 154 (I) | ROQT. 43 bacterial species | ||
| Canabarro et al., 2013 | 20 | 40 | 20 (I) | 60 (I) | Culture. Candida albicans and other yeast | ||
| Griffen et al., 2012 | 29 | 29 | 29 (I) | 58 (I) | 16S rDNA PCR 454 pyrosequencing. Bacteria domain | ||
| Gonçalves et al., 2012 | 15 | 15 | 135 (I) | 135 (I) | ROQT. 10 bacterial species | ||
| Liu et al., 2012 | 3 | 2 | 12 (I) | 12 (I) | 16S rDNA PCR 454 pyrosequencing and Illumina Metagenome high-throughput sequencing. Bacteria domain | ||
| Bringuier et al., 2013 | 10 | 22 | 10 (NA) | 22 (NA) | qPCR. Methanobrevibacter oralis | ||
| Abusleme et al., 2013 | 10 | 22 | 17 (I) | 44 (I) | 16SrDNA PCR 454 pyrosequencing for Bacteria domain and qPCR for Bacteria domain and Actinomyces, Streptococcus and Veillonella genera. | ||
| You et al., 2013a | 10 | 1 | 9 | 10 (P) | 10 (P) | PCR/Cloning/Sanger sequencing. Bacteria domain | |
| You et al., 2013b | 10 | 10 | 10 (P) | 10 (P) | PCR/Cloning/Sanger sequencing. Bacteria domain | ||
FISH from this study was not taken into account, since no control group was evaluated by this method.
NA, not available; H, periodontal health; GAgP, generalized aggressive periodontitis; ChP, chronic periodontitis; RP, refractory periodontitis; P, periodontitis; (I), samples processed individually; (P), samples processed in pool; PCR, polymerase chain reaction; qPCR, quantitative polymerase chain reaction; SDS-PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis; FISH, fluorescence in situ hybridization; DGGE, denaturing gradient gel electrophoresis; ROQT, RNA-oligonucleotide quantification technique.
Three studies used culture methods (Macuch and Tanner, 2000; Murdoch et al., 2004; Canabarro et al., 2012), but Macuch and Tanner (2000) also used a protein electrophoresis technique (SDS-PAGE). The other 38 studies used technologies based on nucleic acid detection as follows: 22 used targeted techniques; 10 used open-ended techniques; and 6 used both approaches. Most studies used techniques based on DNA detection; only 2 studies (Teles et al., 2011; Gonçalves et al., 2012) used a RNA-based detection method—specifically, the RNA–oligonucleotide quantification technique.
Microbial Data
The microorganisms found in statistically significantly higher levels and/or proportion and/or abundance and/or prevalence in periodontitis than in periodontal health or those reported by the authors as being associated with periodontitis were catalogued, and data are summarized in Appendix Table 3.
Table 2 presents the taxa found in at least 1 study in statistically significantly higher levels and/or proportion and/or abundance and/or prevalence in periodontitis than in periodontal health. Three domain systems were identified: Bacteria, Archaea, and Eukarya (represented by Fungi). Bacteria was the main domain detected, and it included 10 phyla (Bacteroidetes, Spirochaetes, Firmicutes, Synergistetes, Proteobacteria, Actinobacteria, Fusobacteria, Chloroflexi, Tenericutes and the Candidatus Saccharibacteria [syn. Candidate division TM7]), the Candidate division Sulphur River 1 (SR1, no rank, http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Info&id=221235&lvl=3&lin=f&keep=1&srchmode=1&unlock, October 29, 2013), 63 bacterial genera, and 108 species/phylotypes. Firmicutes, which harbors mostly Gram-positive bacteria, was the phylum with the highest number of species associated with periodontitis (n = 39), in contrast with Chloroflexi (n = 1). One species from the Archaea domain (Methanobrevibacter oralis HOT 815) and the total levels and proportions of this domain were also associated with periodontitis.
Table 2.
Summary of the Data of the Included Studies: Newly Identified Taxa Associated with Periodontitis*
| Taxa | Chronic Periodontitis Studies | Generalized Aggressive Periodontitis Studies |
|---|---|---|
| Bacteria | ||
| Phylum Actinobacteria | ||
| Actinobacteria class | ||
| Actinomyces naeslundii HOT 176 | Kumar et al., 2003 | |
| Bifidobacterium dentium HOT 588 | Griffen et al., 2012 | |
| Cryptobacterium curtum HOT 579 | Kumar et al., 2003 | |
| Corynebacterium diphtheria HOT 591 | Souto et al., 2006 | |
| Rothia dentocariosa HOT 587 | Kumar et al., 2003 | |
| Slackia exigua HOT 602 | Abiko et al., 2010 | |
| Phylum Bacteroidetes | ||
| Bacteroidia class | ||
| Bacteroidetes [G-1] genus | Abusleme et al., 2013 | |
| Bacteroidaceae [G-1] sp. oral taxon 272 HOT 272 [Bacteroidetes [G-1] sp. OT 272] | Abusleme et al., 2013 | |
| Bacteroidales [G-2] sp. oral taxon 274 HOT 274 [Bacteroidetes clone AU126 / Phylotype AU126 / Bacteroidales OT 274] | Kumar et al., 2003; Li et al., 2006; Griffen et al., 2012 | |
| Bacteroidetes [G-3] genus | Abusleme et al., 2013 | |
| Bacteroidetes [G-3] sp. oral taxon 280 HOT 280 | Abusleme et al., 2013 | |
| Bacteroidetes [G-3] sp. oral taxon 365 HOT 365 | Abusleme et al., 2013 | |
| Bacteroidetes [G-6] genus | Abusleme et al., 2013 | |
| Bacteroidetes [G-6] sp. oral taxon 516 HOT 516 | Abusleme et al., 2013 | |
| Porphyromonas endodontalis HOT 273 | Kumar et al., 2003; Mayanagi et al., 2004; Griffen et al., 2012; Abusleme et al., 2013 | |
| Prevotella denticola HOT 291 | Kumar et al., 2003; Griffen et al., 2012 | |
| Prevotella sp. oral taxon 526 HOT 526 [Prevotella genomo sp. P4] | Griffen et al., 2012 | |
| Prevotella sp. oral taxon 304 HOT 304 | Abusleme et al., 2013 | |
| Alloprevotella tannerae HOT 466 [Prevotella tannerae] | Mayanagi et al., 2004; Griffen et al., 2012 | |
| Phylum Chloroflexi | ||
| Chloroflexi class | ||
| Chloroflexi [G-1] genus | Abusleme et al., 2013 | |
| Chloroflexi [G-1] sp. oral taxon 439 HOT 439 | Abusleme et al., 2013 | |
| Phylum Firmicutes | ||
| Clostridia class | Kumar et al., 2005 | |
| Clostridiales [F-1] [G-1] sp. oral taxon 093 HOT 093 [Oral clone MCE_107] | Griffen et al., 2012 | |
| Catonella genus | Liu et al., 2012 | |
| Catonella sp. oral taxon 164 HOT 164 [Catonella sp. oral clone BR063] | Kumar et al., 2005 | |
| Shuttleworthia C1 | Griffen et al., 2012 | |
| Johnsonella sp. oral taxon 166 HOT 166 [Johnsonella CK051] | Griffen et al., 2012; Abusleme et al., 2013 | |
| Eubacterium [XI] [G-1] genus | Abusleme et al., 2013 | |
| Eubacterium [XI] [G-3] brachy HOT 557 [Eubacterium brachy] | Griffen et al., 2012; Abusleme et al., 2013 | |
| Eubacterium [XI] [G-5] saphenum HOT 759 [Eubacterium saphenum] | Kumar et al., 2003; Mayanagi et al., 2004; Abiko et al., 2010; Griffen et al., 2012; Abusleme et al., 2013 | |
| Eubacterium [XI] [G-6] genus | Abusleme et al., 2013 | |
| Eubacterium [XI] [G-6] minutum HOT 673 | Abusleme et al., 2013 | |
| Mogibacterium genus | Abusleme et al., 2013 | |
| Mogibacterium timidum HOT 042 | Mayanagi et al., 2004; Abiko et al., 2010; Abusleme et al., 2013 | |
| Peptostreptococcaceae [XI] [G-2] genus | Abusleme et al., 2013 | |
| Peptostreptococcaceae [XI] [G-2] sp. oral taxon 091 HOT 091 | Abusleme et al., 2013 | |
| Peptostreptococcaceae [XI] [G-4] genus | Abusleme et al., 2013 | |
| Peptostreptococcaceae [XI] [G-4] sp. oral taxon 103 HOT 103 [phylotype PUS9.170] | Harper-Owen et al., 1999 | |
| Peptostreptoccaceae [XI] [G-4] sp. oral taxon 369 HOT 369 | Abusleme et al., 2013 | |
| Peptostreptococcaceae [XIII] [G-1] genus | Abusleme et al., 2013 | |
| Peptostreptococcaceae [XIII] [G-1] sp. oral taxon 113 HOT 113 [Peptoniphilus oral taxon 113] | Griffen et al., 2012; Abusleme et al., 2013 | |
| Peptostreptococcus genus | Abusleme et al., 2013 | |
| Peptostreptococcus stomatis HOT 112 [Peptostreptococcus sp. oral clone CK035] | Kumar et al., 2005; Griffen et al., 2012; Abusleme et al., 2013 | |
| Peptococcus sp. oral taxon 167 HOT 167 | Abusleme et al., 2013 | |
| Pseudoramibacter genus | Abusleme et al., 2013 | |
| Pseudoramibacter alactolyticus HOT 538 | Abusleme et al., 2013 | |
| Filifactor genus | Abusleme et al., 2013 | |
| Filifactor alocis HOT 539 | Kumar et al., 2003; Kumar et al., 2005; Schlafer et al., 2010; Griffen et al., 2012, Abusleme et al., 2013 | Schlafer et al., 2010 |
| Lachnospiraceae [G-8] genus | Abusleme et al., 2013 | |
| Lachnospiraceae [G-8] sp. oral taxon 500 HOT 500 [Lachnospiraceae JM048] | Griffen et al., 2012; Abusleme et al., 2013 | |
| Lachnospiraceae [G-4] genus | Abusleme et al., 2013 | |
| Stomatobaculum sp. oral taxon 373 HOT 373 [Lachnospiraceae [G-4] sp. OT 373] | Abusleme et al., 2013 | |
| Unclassified clostridiales ord | Abusleme et al., 2013 | |
| Negativicutes class | ||
| Anaeroglobus geminatus HOT 121 [Megasphaerao oral clone BB166] | Kumar et al., 2003; Kumar et al., 2005; Griffen et al., 2012 | |
| Centipeda genus | Drescher et al., 2010 | Drescher et al., 2010 |
| Dialister invisus HOT 118 [Dialister sp. oral strain GBA27] | Kumar et al., 2003 | |
| Dialister sp. oral taxon 119 HOT 119 [Dialister sp. oral clone MCE7_134] | Kumar et al., 2005 | |
| Dialister pneumosintes HOT 736 | Mayanagi et al., 2004; Kumar et al., 2005 | |
| Megasphaera sp. oral clone MCE3_141 | Kumar et al., 2005 | |
| Megasphaera sp. oral taxon 123 HOT 123 [Megasphaera sp. oral clone BS073] | Kumar et al., 2005 | |
| Mitsuokella sp. HOT 131 [Selenomonas CS002] | Gonçalves et al., 2012 | |
| Selenomonas genus | Liu et al., 2012; Drescher et al., 2010 | Drescher et al., 2010 |
| Selenomonas sputigena HOT 151 | Kumar et al., 2003; Mayanagi et al., 2004; Griffen et al., 2012; Abusleme et al., 2013 | Gonçalves et al., 2012 |
| Selenomonas sp. oral clone D0042 | Kumar et al., 2005 | |
| Selenomonas sp. oral clone 126 HOT 126 [Selenomonas EY047] | Griffen et al., 2012 | |
| Selenomonas dianae HOT 139 | Griffen et al., 2012 | |
| Veillonellaceae [G-1] genus | Abusleme et al., 2013 | |
| Veillonellaceae [G-1] sp. oral taxon 129 HOT 129 | Griffen et al., 2012 | |
| Veillonellaceae [G-1] sp. oral taxon 132 HOT 132 | Abusleme et al., 2013 | |
| Veillonellaceae [G-1] sp. oral taxon 155 HOT 155 | Abusleme et al., 2013 | |
| Bacilli class | ||
| Enterococcus faecalis HOT 604 | Colombo et al., 2002; Souto et al., 2006; Souto and Colombo, 2008; da Silva-Boghossian et al., 2011 | |
| Streptococcus sp. oral strain 9F | Kumar et al., 2005 | |
| Streptococcus sp. oral taxon 061 HOT 061 [Streptococcus sp. oral clone DP009] | Kumar et al., 2005 | |
| Streptococcus constellatus HOT 576 | Abusleme et al., 2013 | |
| Streptococcus anginosus HOT 543 | Abusleme et al., 2013 | |
| Streptococcus sp. oral taxon 071 HOT 071 | Abusleme et al., 2013 | |
| Staphylococcus aureus HOT 550 | Souto et al., 2006 | |
| Phylum Fusobacteria | ||
| Fusobacteriia class | ||
| Fusobacterium oral taxon A71 | Griffen et al., 2012 | |
| Fusobacterium nucleatum subsp. animalis HOT 420 [Fusobacterium animalis] | Abusleme et al., 2013 | |
| Leptotrichiaceae [G-1] sp. oral taxon 210 HOT 210 | Griffen et al., 2012 | |
| Leptotrichia sp. oral taxon 498 HOT 498 [Leptotrichia IK040] | Griffen et al., 2012 | |
| Leptotrichia EX103 | Griffen et al., 2012 | |
| Sneathia sanguinegens HOT 837 | Abusleme et al., 2013 | |
| Phylum Proteobacteria | ||
| Alphaproteobacteria class | ||
| Bartonella sp. | Colombo et al., 2002 | |
| Gammaproteobacteria class | ||
| Acinetobacter baumannii HOT 554 | da Silva-Boghossian et al., 2011; Souto et al., 2006 | da Silva-Boghossian et al., 2011 |
| Aggregatibacter sp. oral taxon 458 HOT 458 [Aggregatibacter AY349380] | Griffen et al., 2012 | |
| Escherichia coli HOT 574 | Colombo et al., 2002; Souto et al., 2006 | |
| Klebsiella pneumoniae HOT 731 | Souto et al., 2006 | |
| Pseudomonas sp. | Ledder et al., 2007 | |
| Pseudomonas aeruginosa HOT 536 | Souto et al., 2006 | |
| Deltaproteobacteria class | ||
| Desulfobulbus genus | Abusleme et al., 2013 | |
| Desulfobulbos sp. oral taxon 041 HOT 041 [Clone Desulfobulbus sp. R004 / Desulfobulbus sp. oral clone R004 / Desulfobulbos sp. OT 041 / Desulfobulbus R004] | Kumar et al., 2005; Griffen et al., 2012; Abusleme et al., 2013 | |
| Desulfobulbus oral clone CH031 | Kumar et al., 2005 | |
| Epsilonproteobacteria class | ||
| Campylobacter sputorum HOT 776 | Kumar et al., 2005 | |
| Campylobacter sp. oral taxon 044 HOT 044 [Campylobacter sp. oral clone BB120] | Kumar et al., 2005 | |
| Phylum Spirochaetes | ||
| Spirochaetia class | ||
| Treponema genus | Abusleme et al. 2013 | |
| Treponema phylogroup II | You et al., 2013a | Riep et al., 2009; You et al., 2013a |
| Treponema phylogroup III | You et al., 2013a | You et al., 2013a |
| Treponema phylogroup V | You et al., 2013a | You et al., 2013a |
| Treponema phylogroup I:OTU 8P68 | You et al., 2013a | You et al., 2013a |
| Treponema sp. oral taxon 246 HOT 246 [Treponema II CT1] | Griffen et al., 2012 | |
| Treponema phylogroup II:OTU 1P26 | You et al., 2013a | You et al., 2013a |
| Treponema amylovorum HOT 541 | Griffen et al., 2012 | |
| Treponema lecithinolyticum HOT 653 | Kumar et al., 2003; Griffen et al., 2012; Abusleme et al., 2013; | Riep et al., 2009 |
| Treponema medium HOT 667 | Asai et al., 2002; Kumar et al., 2003; Mayanagi et al., 2004; Griffen et al., 2012; Abusleme et al., 2013 | |
| Treponema vincentii HOT 029 | Willis et al., 1999; Asai et al., 2002; Griffen et al., 2012 | |
| Treponema sp. oral taxon 230 HOT 230 | Griffen et al., 2012 | |
| Treponema sp. oral taxon 490 HOT 490 [Treponema E25-8] | Griffen et al., 2012 | |
| Treponema E_D_05_72 | Griffen et al., 2012 | |
| Treponema sp. oral taxon 237 HOT 237 | Abusleme et al., 2013 | |
| Treponema maltophilum HOT 664 | Abusleme et al., 2013 | |
| Treponema sp. oral taxon 257 HOT 257 [Treponema D36ER-1] | Abusleme et al., 2013 | |
| Treponema sp. oral taxon 249 HOT 249 | Abusleme et al., 2013 | |
| Treponema sp. parvum HOT 274 | Abusleme et al., 2013 | |
| Treponema sp. oral taxon 253 HOT 253 | Abusleme et al., 2013 | |
| Treponema sp. oral taxon 258 HOT 258 | Abusleme et al., 2013 | |
| Phylum Synergistetes | Vartoukian et al., 2009 | |
| Unclassified class | ||
| Synergistetes Oral Clone A2F_22 [“Synergistetes” OTU 4.2 A2F_22-OTU 4.2 FJ490414] | Vartoukian et al., 2009 | |
| Synergistes oral taxon G36 | Griffen et al., 2012 | |
| Fretibacterium sp. oral taxon 359 HOT 359 [Deferribacteres sp. oral clone BH007 / Synergistetes OTU 7P1] | Kumar et al., 2005; You et al., 2013b | |
| Fretibacterium sp. oral taxon 360 HOT 360 [Deferribacteres clone BH017 / Synergistes oral taxon 360 / Synergistetes OTU 7P22 / Synergistes [G-3] sp. OT 360] | Kumar et al., 2003; Griffen et al., 2012; You et al., 2013b; Abusleme et al., 2013 | |
| Fretibacterium sp. oral taxon 361 HOT 361 [Synergistes [G-3] sp. OT 361] | Abusleme et al., 2013 | |
| Fretibacterium sp. oral taxon 362 HOT 362 [Deferribacteres clone D084 / Synergistetes [G-3] sp. OT 362 / Synergistetes OTU 2P9 / Synergistetes OTU 6P18] | Kumar et al., 2003; You et al., 2013b; Abusleme et al., 2013 | |
| Fretibacterium fastidiosum HOT 363 [Deferribacteres sp. oral clone W090 / Synergistetes [G-3] sp. OT 363 / Synergistetes OT 4P12] | Kumar et al., 2005; You et al., 2013b; Abusleme et al., 2013 | |
| Fretibacterium sp.oral taxon 453 HOT 453 [Synergistes OT 453] | Griffen et al., 2012 | |
| Phylum Tenericutes | ||
| Mollicutes class | ||
| Mycoplasma genus | Abusleme et al., 2013 | |
| Mycoplasma facium HOT 606 | Abusleme et al., 2013 | |
| Phylum Candidatus Saccharibacteria (Syn. Candidate division TM7) | Brinig et al., 2003; Ouverney et al., 2003; Liu et al., 2012 | |
| TM7 [G-1] sp. oral taxon 346 HOT 346 [TM7 401H12] | Griffen et al., 2012; Abusleme et al., 2013 | |
| TM7 [G-1] sp. oral taxon 347 HOT 347 | Griffen et al., 2012 | |
| TM7 [G-1] sp. oral taxon 349 HOT 349 | Griffen et al., 2012; Abusleme et al., 2013 | |
| TM7 [G-5] genus | Abusleme et al., 2013 | |
| TM7 [G-5] sp. oral taxon 356 HOT 356 [TM7 Clone I025] | Kumar et al., 2003; Brinig et al., 2003; Abusleme et al., 2013 | |
| Candidate division Sulphur River 1 (Candidate division SR1) | ||
| SR1 [G-1] sp. oral taxon 345 HOT 345 [OP11 clone X112 / phylotype X112] | Kumar et al., 2003; Li et al., 2006 | |
| Archaea | Lepp et al., 2004; Li et al., 2009 | Matarazzo et al., 2011 |
| Phylum Euryarchaeota | ||
| Methanobacteria class | ||
| Methanobrevibacter oralis HOT 815 [Uncultured Methanobrevibacter isolate mcrA-II] | Bringuier et al., 2013 | |
| Eukarya | ||
| Fungi Kingdom | Canabarro et al., 2012 |
As found in statistically significantly higher levels and/or prevalence and/or proportion and/or abundance in periodontitis than in periodontal health.
[Brackets] indicate other nomenclatures for the species/phylotype used on the different studies.
HOT, Human Oral Taxon (designations provided in accordance with the Human Oral Microbiome Database).
To estimate the current weight of evidence of newly identified pathogens associated with periodontitis, the data of Table 2 were subsetted into the following categories: taxa found in statistically significantly higher levels and/or proportion and/or prevalence and/or abundance in periodontitis than in periodontal health from 3 to 5 studies (moderate evidence) or in 2 studies (some evidence) (Table 3). Seventeen species/phylotypes, the phylum Candidatus Saccharibacteria, and the Archaea domain were included in the moderate evidence category and other 15 taxa in the some evidence category.
Table 3.
Weight of Evidence for Newly Identified Periodontal Pathogens in the Etiology of Periodontitis
| Taxa | Studies, n |
|---|---|
| Evidence: Moderate | |
| Phylum Bacteroidetes | |
| Bacteroidales [G-2] sp. oral taxon 274 HOT 274 (–)a [Bacteroidetes clone AU126 / Phylotype AU126 / Bacteroidales OT 274] | 3 |
| Porphyromonas endodontalis HOT 273 (–)a | 4 |
| Phylum Firmicutes | |
| Eubacterium [XI] [G-5] saphenum HOT 759 (+)a [Eubacterium saphenum] | 5 |
| Mogibacterium timidum HOT 042 (+)a | 3 |
| Peptostreptococcus stomatis HOT 112 (+)a [Peptostreptococcus sp. oral clone CK035] | 3 |
| Filifactor alocis HOT 539 (+)a | 5 |
| Anaeroglobus geminatus HOT 121 (–)a [Megasphaera oral clone BB166] | 3 |
| Selenomonas sputigena HOT 151 (–)a | 5 |
| Enterococcus faecalis HOT 604 (+)b | 4 |
| Phylum Proteobacteria | |
| Desulfobulbus sp. oral taxon 041 HOT 041 [Desulfobulbus sp. oral clone R004 / Desulfobulbos sp. OT 041 / Desulfobulbus R004]c | 3 |
| Phylum Spirochaetes | |
| Treponema lecithinolyticum HOT 653 (–)a | 4 |
| Treponema medium HOT 667 (–)a | 5 |
| Treponema vincentii HOT 029 (–)a | 3 |
| Phylum Synergistetes | |
| Fretibacterium sp. oral taxon 360 HOT 360 [Deferribacteres clone BH017 / Synergistes oral taxon 360 / Synergistetes OTU 7P22 / Synergistes [G-3] sp. OT 360]c | 4 |
| Fretibacterium sp. oral taxon 362 HOT 362 [Deferribacteres clone D084 / Synergistetes [G-3] sp. OT 362 / Synergistetes OTU 2P9 / Synergistetes OTU 6P18]c | 3 |
| Fretibacterium fastidiuosum HOT 363 (–)a [Deferribacteres sp. oral clone W090 / Synergistetes [G-3] sp. OT 363 / Synergistetes OT 4P12] | 3 |
| Phylum Candidatus saccharibacteria (Syn. Candidate division TM7) | 3 |
| TM7 [G-5] sp. oral taxon 356 HOT 356 [TM7 clone I025]c | 3 |
| Archaea domain | 3 |
| Evidence: Some | |
| Phylum Bacteroidetes | |
| Prevotella denticola HOT 291 (–)a | 2 |
| Alloprevotella tannerae HOT 466 (–)a [Prevotella tannerae] | 2 |
| Phylum Firmicutes | |
| Selenomonas genus (–)a | 2 |
| Johnsonella sp. oral taxon 166 HOT 166 [Johnsonella CK051]c | 2 |
| Eubacterium [X1] [G-3] brachy HOT 557 (+)a [Eubacterium brachy ] | 2 |
| Peptostreptococcaceae [XIII] [G-1] sp. oral taxon 113 HOT 113 [Peptoniphilus oral taxon 113]c | 2 |
| Lachnospiraceae [G-8] sp. oral taxon 500 HOT 500 [Lachnospiraceae JM048]c | 2 |
| Dialister pneumosintes HOT 736 (–)a | 2 |
| Phylum Proteobacteria | |
| Acinetobacter baumannii HOT 554 (–)a | 2 |
| Escherichia coli HOT 574 (–)b | 2 |
| Phylum Spirochaetes | |
| Treponema phylogroup II (–)a | 2 |
| Phylum Synergistetes | |
| Fretibacterium sp. oral taxon 359 HOT 359 [Deferribacteres sp. Oral Clone BH007 / Synergistetes OTU 7P1]c | 2 |
| Phylum Candidatus saccharibacteria (Syn. Candidate division TM7) | |
| TM7 [G-1] sp. oral taxon 346 HOT 346 [TM7 401H12]c | 2 |
| TM7 [G-1] sp. oral taxon 349 HOT 349c | 2 |
| Candidate division Sulphur River 1 (Candidate division SR1) | |
| SR1 [G-1] sp. oral taxon 345 HOT 345 [OP11 clone X112 / Phylotype X112]c | 2 |
Species, phylothype, phylum, or domain found in statistically significantly higher levels and/or prevalence and/or proportion and/or abundance in periodontitis than in periodontal health in 3, 4, or 5 studies (moderate evidence) or in 2 studies (some evidence). [Brackets] indicate other nomenclatures for the species or phylotype used among the different studies.
, Gram positive; –, Gram negative.
Anaerobic.
Facultative anaerobic.
Species not-yet-cultivable.
Appendix Table 4 presents the same type of data of Table 2 but for the known pathogens. Recognized periodontal pathogens such as the members of the red complex, A. actinomycetemcomitans, and certain members of the orange complex were found in statistically significantly higher levels and/or proportions and/or prevalence in a number of studies using targeted and open-ended techniques. For example, P. gingivalis, T. forsythia and T. denticola were statistically significantly elevated in periodontitis than in health in 9 studies.
Discussion
This is the first systematic review that assessed the current weight of evidence concerning new candidate periodontal pathogens after 12 yr of what could be considered the “modern era” of oral microbiology. We estimated that at this point no microorganism could be set as a true new periodontal pathogen with strong evidence, since the number of studies that associated each of the taxa with periodontitis is still low—from 1 to 5. Therefore, the highest evidence category specified was moderate.
Four microorganisms of the 17 taxa included in the moderate evidence category are not-yet-cultivable, and 13 have been cultivated before. Five of the cultivable species are Gram positive (Eubacterium saphenum, Mogibacterium timidum, Peptostre-ptococcus stomatis, Filifactor alocis and Enterococcus faecalis), while all the other 8 (Bacteroidales [G-2] sp. oral taxon 274, Porphyromonas endodontalis, Treponema lecithinolyticum, Treponema medium, Treponema vincentii, Anaeroglobus geminatus—also known as Megasphaera oral clone BB166, Selenomonas sputigena, Fretibacterium fastidiuosum) are Gram negative and anaerobic, characteristics of most of the microorganisms involved in polymicrobial infections. Five of these new candidate periodontal pathogens belong to the phyla Bacteroidetes and Spirochaetes, which include several known periodontal pathogens, such as P. gingivalis, T. forsythia, T. denticola, and T. socranskii and species from the genera Prevotella (Socransky et al., 1998). Seven species were from the Firmicutes phylum, and the other 5 species/phylotypes were distributed among the Proteobacteria, Synergistetes, and Candidatus Saccharibacteria phyla. The phylum Firmicutes harbors genera previously associated with periodontal health (e.g., Streptococcus) or disease (e.g., Eubacterium and Selenemonas) (Socransky et al., 1998; Kumar et al., 2003), and several other cultivable or not-yet-cultivable microorganisms from this phylum fell into the moderate (e.g., F. alocis, E. faecalis) or some evidence (Dialister pneumosintes, Lachnospiraceae [G-8] sp. oral taxon 500) categories.
Almost all bacterial species listed as a suspected periodontal pathogen in the present study are mostly found in the oral cavity and rarely involved in extraoral infections. One exception was E. faecalis, which is part of the commensal microbiota of the human gastrointestinal tract but may also act as an opportunistic pathogen when spreading to other mucosa or skin tissues (Vu and Carvalho, 2011). With respect to oral diseases, E. faecalis has been associated with root canal treatment failure (Wang et al., 2012). It was interesting to note that all the evidence supporting E. faecalis as a candidate periodontal pathogen came out of studies that evaluated Brazilian patients (Colombo et al., 2002; Souto et al., 2006; Souto and Colombo 2008; da Silva-Boghossian et al., 2011). This could be an example of a geographic specificity, since it has been suggested that the periodontal microbiota may show specific differences among countries (Haffajee et al., 2004). However, this information would need to be confirmed by future studies evaluating the prevalence and levels of this microorganism in other populations. The other exceptions of microorganisms associated with periodontitis in the present review that may inhabit extraoral environments are S. sputigena, T. medium, and species from the Synergistetes and Candidatus Saccharibacteria phyla. S. sputigena is a normal resident of the upper respiratory tract and has been associated with a case of septicemia (McCarthy and Carlson, 1981), while T. medium has been detected in the human brain cortex of subjects with Alzheimer but not in healthy controls (Riviere et al., 2002). Species from the Synergistetes phylum, such as Synergistetes jonesii and Peritoneal fluid isolate RMA 16088, have been isolated from the peritoneal fluid (Horz et al., 2006). Species from the Candidatus Saccharibacteria phylum have been detected in vaginosis and bowel disease (Fredricks et al., 2005; Kuehbacher et al., 2008). The presence of microorganisms in the subgingival biofilm that are also associated with extraoral diseases may be an important link between oral and systemic infections and should be considered in further studies.
Another finding that deserves attention in the present review concerns the Archaea domain, which also fell into the moderate evidence category. Among the 41 studies included in this review, only 5 searched for Archaea, and 4 of them showed an association between this domain and periodontitis (Lepp et al., 2004; Li et al., 2009; Matarazzo et al., 2011; Bringuier et al., 2013). Although the fifth study (Vianna et al., 2008) did not find statistically significant higher prevalence or counts of metanogenic Archaea in subjects with periodontitis in comparison with periodontally healthy subjects, this taxa was not detected in any of the healthy subjects evaluated. Hence, while the number of studies that examined Archaea is still modest, all of them suggested some type of association between this domain and periodontitis, and it would be important to conduct future investigations to elucidate this evidence more clearly. To date, Archaea has not been associated with other infections in the body.
Some of the microorganisms showing moderate evidence of being periodontal pathogens have not yet been cultivated. It was possible to detect these species due to molecular diagnostic approaches, such as polymerase chain reaction and DNA probes introduced in the late 1990s and, more recently, the open-ended polymerase chain reaction/sequencing techniques. The results of studies using these techniques have broadened our knowledge about oral cavity ecology, including the possible role of some not-yet-cultivable taxa in the etiology of periodontitis. The Candidatus Saccharibacteria and Synergistetes phyla, for example, comprise mainly uncultivated species, and many of them fell into the moderate or some evidence categories. Some of the studies using independent-culture techniques have also contributed to showing that the diversity of certain genera already associated with periodontitis, such as Treponema, might be greater than previously reported. It is interesting to observe that 21 species from the Treponema genus, other than those already recognized as periodontal pathogens, have been found in statistically significant higher levels and/or proportions and/or abundance in subjects with periodontitis in 9 studies (Table 2).
The number of plaque samples evaluated by the various studies is also an important point to consider. It has been advocated that the evaluation of large number of plaque samples per patient is a crucial requirement for obtaining reliable information about the etiology of periodontitis (Haffajee and Socransky, 2006). In this regard, there is an important difference between the targeted and open-ended molecular techniques. For instance, while the open-ended 16S rDNA pyrosequencing approaches allow an in-depth characterization of microbial diversity, these techniques are still relatively costly; therefore, the studies using pyrosequencing have evaluated a limited number of plaque samples. However, some of the target techniques, such as checkerboard DNA-DNA hybridization and RNA–oligonucleotide quantification technique, allow the evaluation of thousands of plaque samples at a relatively low cost. Specifically, one-third of the studies included in this review used open-ended diagnostic tests and evaluated approximately 230 and 630 subgingival plaque samples from periodontally healthy or periodontitis subjects, respectively, in contrast to 3,220 and 10,160 analyzed by the two-thirds of the studies using targeted approaches. Thus, the combination of open-ended and targeted methods seems to be our best option toward full understanding of the etiology and, consequently, the treatment of periodontitis. Probes or primers for the suspected new pathogens detected by the 16S rDNA pyrosequencing studies might be developed and used on a large scale by target techniques. In an even more optimistic future perspective, the cost associated with this next-generation sequencing technology will be reduced and the processing of the data would be simplified, allowing for the sequencing of large numbers of samples.
Overall, the data of this systematic review support the notion that the subgingival pocket is a complex environment that harbors a highly diverse microbiota. It seems evident that other microorganisms besides the already known periodontal pathogens might be involved in the onset and/or progression of periodontitis. Nonetheless, it is essential to emphasize that this review provides only the first evidence necessary to associate a microorganism with the etiopathogenesis of periodontitis—that is, higher levels and/or proportions of the species in cases than in controls (association studies). Indeed, the etiologic role of these microorganisms would need to be confirmed by risk assessment and interventional (i.e., elimination) studies to evaluate whether their reduction or elimination would be accompanied by clinical improvements and whether their persistence would lead to disease progression (Socransky, 1979). In addition, further investigation into their mechanisms of pathogenicity and their ability to promote or evade host immune response would be required.
Another important idea to keep in mind while interpreting the results of association studies is the “causal versus casual” concept. The fact that a microorganism is found in higher levels and proportions in disease than in health might not be sufficient to determine whether it actually initiated the disease process or was merely favored by the inflammatory environment associated with periodontitis. In recent years, this discussion around causality/casualty has gained new momentum with the introduction of novel theories about the ecological events associated with periodontal destruction (Marsh, 2003; Socransky and Haffajee, 2005; Darveau, 2010; Hajishengallis et al., 2011; Hajishengallis and Lamont, 2012). Although they differ in several aspects, a common principle of these theories is that there is a reciprocal interaction between the environment and the microbiota; specifically, environmental factors may lead to the selection or overgrowth of certain pathogens. An interesting hypothesis has suggested that certain known periodontal pathogens—termed “keystone pathogens”—that have the capacity to evade host response would be able to mediate the microbial community’s conversion into dysbiosis, and a wide perturbation of this community would cause and/or sustain the process of periodontal breakdown (Hajishengallis et al., 2011). Apparently, these keystone pathogens might elevate the virulence of the entire biofilm through specific interactions with accessory pathogens (Hajishengallis and Lamont, 2012). The results of the present review might serve as the initial step for the identification of new keystone or accessory pathogens, contributing to future preventive and therapeutic strategies for periodontitis.
In summary, the results of this systematic review support moderate evidence for the association of 17 species/phylotypes from the Bacteria domain, the Candidatus Saccharibacteria phylum, and the Archaea domain with the etiology of periodontitis. These findings would be useful to guide future investigations on the actual role of these suspected new pathogens in the onset and progression of this disease.
Supplementary Material
Footnotes
A supplemental appendix to this article is published electronically only at http://jdr.sagepub.com/supplemental.
This work was partly supported by the São Paulo Research Foundation, grant 2012/20915-0 and 308124/2013-8 from The National Council for Scientific and Technological Development (CNPq, Brazil).
The authors declare no potential conflicts of interest with respect to the authorship and/or publication of this article.
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