Table 1.

Important bacterial genera and species found in the human oral cavity, and their association with oral health or diseases.

Genus and Species	Gram Type	Growth Conditions	Clinical Relevance	References
Actinomyces	Gram+	facultative anaerobe	adhere to oral tissue, play an important role in biofilm formation, contribute to caries and periodontitis	[1,2,8,32]
Actinomyces naeslundii	Gram+	facultative anaerobe	associated with healthy microbiota, interaction with Streptococcus mutans, involved in initial dental biofilm formation, attaches to the pellicle	[33,34,35]
Actinomyces radicidentis	Gram+	facultative anaerobe	found in infected root canals of teeth and tissue	[32,36]
Aggregatibacter actimycetemcomitans	Gram−	facultative anaerobe	associated with peridodontitis.	[9,10]
Brevundimonas diminuta	Gram−	aerobe	periodontal pathogen, in subgingival niche	[37]
Campylobacter consisus	Gram−	anaerobe	in subgingival niche, isolated from the oral cavity of patients with gingivitis and periodontitis, but with no clear association to either disease or other human oral inflammatory diseases	[38]
Campylobacter curvus	Gram−	anaerobe	subgingival; no significant evidence for causing periodontal disease, but found it higher proportions at periodontitis sites as compared to healthy ones	[39]
Campylobacter ureolyticus	Gram−	anaerobe	gastrointestinal pathogen; present in subgingival plaque; associated with poor oral hygiene.	[40]
Corynebacterium	Gram+	aerobe, facultative anaerobe	found in dental plaque, associated with the formation of dental calculi	[41]
Dialister	Gram−	anaerobe	D. pneumosintes and D. invisus are periodontal pathogens, have been associated with refractory periodontitis, acute necrotizing ulcerative gingivitis, endodontic infections; subgingival	[37,42]
Enterococcus	Gram+	anaerobe	E. faecalis has been related to caries, endodontic infections, periodontitis, and peri-implantitis, biofilm former able to integrate in the oral biofilm in situ	[43]
Filifactor alocis	Gram+	anaerobe	associated with periodontitis.	[9,10]
Fusobacterium nucleatum	Gram−	anaerobe	member of the “orange complex“, periodontal pathogen, involved in primary infections of endodontal lesions, associated with subgingival plaque, peri-implantitis, gingivitis, advanced irreversible forms of periodontitis, associated with dental fluorosis, bridging microorganism which can co-aggregate with early and late colonizers, plays a major role in the maturation of the oral biofilm, one of the most abundant genera in the native biofilm	[12,13,44,45,46]
Fusobacterium pseudoperiodonticum	Gram−	anaerobe	isolated from periodontitis lesions and from the tongue	[47]
Gemella sanguinis	Gram+	facultative anaerobe	periodontal pathogen; affects the periodontal health status and is prevalent in refractory periodontitis; in subgingival niche	[5,37]
Haemophilus parainfluenzae	Gram−	facultative anaerobe	significantly more prevalent in periodontal health than periodontitis	[37]
Lactobacillus	Gram+	anaerobe	associated with carious lesions, anticaries potential, can inhibit tooth decay by limiting growth and virulence properties of Streptococcus mutans”, dominant genera in the pulp chamber of apical periodontitis (rat model)	[45,48,49,50]
Lautropia mirabilis	Gram−	facultative anaerobe	localized on the back of the tongue, significantly more prevalent in periodontal health than periodontitis	[37,51]
Megaspahera elsdenii	Gram−	anaerobe	one of the most abundant genera in the native biofilm
Megaspaera stantonii	Gram−	anaerobe	one of the most abundant genera in the native biofilm
Neisseria	Gram−	aerobic	often found resistant to antibiotics in periodontal patients undergoing therapy; affect the oral health status;	[5,52]
Neisseria mucosa	Gram−	aerobic	Found in gingival plaque, affect the periodontal health status	[53]
Neisseria subflava	Gram−	aerobe	populates the tongue dorsum, affects the periodontal health status	[53]
Olsenella	Gram+	obligate anaerobe	associated with carious lesions	[49]
Porphyromonas gingivalis	Gram−	anaerobe	member of the “red complex”, involved in periodontitis, primary infections of endodontal lesions, associated with peri-implantitis	[34,54]
Prevotella denticola	Gram−	anaerobe	dominant bacteria in oral lichen planus; abundance in the oral cavity can lead to mucosal inflammation and oral lichen planus; associated with periodontitis.	[4,5,9,10,12,13,55]
Prevotella melaninogenica	Gram−	anaerobe	commensal bacterium, member of normal human oral microbiota	[56]
Rothia mucilaginosa	Gram+	aerobe	found on the tongue (up to 6%), found at high abundance on oral leukoplakia, significantly more prevalent in periodontal health than periodontitis, marker for early childhood caries	[3,37,57]
Schaalia odontolytica	Gram+	anaerobe	associated with healthy microbiota	[46]
Selenomonas sp. oral taxon 136	Gram−	anaerobe	periodontal pathogen, significantly prevalent in refractory periodontitis, in subgingival niche	[37]
Staphylococcus schleiferi	Gram+	facultative anaerobe	veterinary pathogen, but can also cause opportunistic infections in humans	[58]
Streptococcus koreensis	Gram+	facultative anaerobe	associated with subgingival dental plaque/periododitis lesion	[58]
Streptococcus parasanguinis	Gram+	facultative anaerobe	“pioneer species”, colonizes teeth fast; involved in the periodontal biofilm, periodontal pathogen; dynamic interaction with A. actinomycetemcomitans, a late colonizer and periodontal pathogen; together with A. actinomcetemcomitans and Filifactor alocis: may be biomarker for periodontitis	[40,45,59]
Streptococcus pneumoniae	Gram+	facultative anaerobe	associated with periodontal health; associated with sinusitis	[60]
Streptococcus salivarius	Gram+	facultative anaerobe	colonizes the tongue associated with carious lesions	[45,49]
Streptococcus sanguinis	Gram+	facultative anaerobe	“pioneer species”, colonizes teeth fast; important for supragingival biofilm formation; may suppress the generation of caries; antagonism between S. sanguinis and S. mutans; associated with oral health	[37,61]
Streptococcus thermophilus	Gram+	facultative anaerobe	poor biofilm former	[32]
Tannerella forsythia	Gram−	anaerobe	member of the “red complex”; in subgingival niche; associated with periodontal disease and peri-implantitis	[4,5,9,10,12,13,62]
Tannerella sp. Oral taxon HOT-286	Gram−	anaerobe	associated with periodontal health; in subgingival niche; may provide protection from acquisition of T. forsythia	[62]
Veillonella	Gram−	anaerobe	found on the tongue, the buccal mucosa, and in saliva, interactions between Streptococcus species and Veillonella species in the early stages of oral biofilm formation; associated with caries, consistently resistant to antibiotics in periodontal patients undergoing therapy; presence in children may predict the development of future caries, indication for poor oral health.	[1,3,8,52]
Veillonella atypica	Gram−	anaerobe	early colonizers in oral biofilm formation; periodontal pathogen significantly prevalent in refractory periodontitis; subgingival	[37,52]
Veillonella dispar	Gram−	anaerobe	early colonizers in oral biofilm formation	[52]
Veillonella parvula	Gram−	anaerobe	associated with severe early childhood caries and intraradicular infections (abscess, apical root canals, and dentinal tubules); early colonizers in oral biofilm formation	[52]