Table 1 . Main Distinctive Features of the Mcrobiota Associated With Different Types of Endodontic Infections .

Type of infections	Primary infection Chronic Apical Periodontitis/Acute Apical Abscess		Persistent/Secondary Infections Filling Stage/Treated Teeth
Community	Mixed		Mixed, sometimes single
No. taxa/case	10–20		1–5
Uncultivated bacteria	40%–55%		42%-55%
Most prevalent groups	Gram-negative/gram-positive anaerobes		Gram-positive/gram-negative facultative/anaerobes
	Most prevalent species (% prevalence)	Virulence factors	Most prevalent species (% prevalence)	Virulence factors
	Filifactor alocis G +/ An (48)	Metal-dependent proteases Trypsin-like proteases Sialoglycoproteases	Enterococcus faecalis G +/ F (64-78)	Hemolysin/cytolysin Gelatinase (GelE) Hyaluronidase Enterococcal surface protein (Esp) E. faecalis regulator (Fsr) Aggregation substance (AS) Microbial surface component recognizing adhesive matrix molecule adhesin of collagen from Enterococci (MSCRAMM Ace) Serine protease (SprE) Sex pheromones Second collegen adhesin of E. faecalis (Scm) Lipoteichoic acid Capsule Cell wall polysaccharide Extracellular superoxide Heat-shock proteins
	Pseudoramibacter alactolyticus G +/An (52)	Chemotaxis	Streptococcus anginosus G +/ F (7-53)	Polysaccharide capsule Pyrogenic exotoxins Hyaluronidase Peptidoglycan Lipoteichoic acid Metabolites
	Parvimonas spp. G +/ An P. micra (formerly Peptostreptococcus micros) (22-78)	Peptidases Hyaluronidase Capsule H2S Capsule Surface proteins Collagenase	Streptococcus mitis G +/ F (7-46) Streptococcus sanguinis G +/ F (7-28) Filifactor alocis G +/ An (46-57)	Choline-binding proteins (CBPs) Hydrogen peroxide Metal-dependent proteases Trypsin-like proteases Sialoglycoproteases
	Treponema spp. G -/ F T. maltophilum (89) T. socranskii (75) T. denticola (36-79) T. parvum (22-39)	Biofilm Motility Cystalysin Outer membrane dentilisin protease Lipoprotein complex Toxin antitoxin systems Transposases Trypsin-like protease Periplasmic flagella Major surface protein (Msp) Chymotrypsin-like protease complex Extracellular or membrane-associated proteolytic and hydrolytic enzymes Lipooligosaccharide Lipoprotein Phospholipases Metabolites (acetic and lactic acids, H2S) Heat-shock proteins	Actinomyces spp. G +/ An A. israelii (1-20) A. naeslundii (7-20) A. viscosus (7)	Fimbriae
	Tannerela forsythia G -/ An (30-64)	Trypsin-like protease SiaHI sialidases NanH sialidases S-layer Lipopolysaccharide Acid phosphatase Metabolites (acetic, propionic, butyric, isovaleric and phenylacetic acids) Apoptosis-inducing factor Heat-shock proteins	Parvimonas micra G +/ An (5-60)	Peptidases Hyaluronidase Capsule H2S
	Porphyromonas spp. G -/ An P. endodontalis (15-68) P. gingivalis (30)	Fimbriae Trypsin-like proteinase Cysteine protease Biofilm Lipopolysaccharide Capsule Outer membrane proteins Outer membrane vesicles Acid phosphatase Metabolites (butyric and propionic acids, indole, H2S) Lipoproteins Phospholipase DNase Hyaluronidase Fibrinolysin Chondroitin sulfatase Hemolysins Heat-shock proteins	Lactobacillus spp. G +/ F (7-35)	See primary infection
	Fusobacterium spp. G -/ An F. nucleatum (19-86) F. necrophorum (23) F. periodonticum (19)	Heat shock proteins Lipopolysaccharide Outer membrane proteins Capsule Metabolites (butyric and propionic acids, ammonia, indole) Serine protease Synergistic interaction with facultative organisms or other anaerobes	Olsenella spp. G +/ An O. profusa (7-100) O. uli (27-67)	See primary infection
	Prevotella spp. G -/ An P. denticola (77) P. oralis (40) P. baroniae (35) P. buccae (29) P. melaninogenica (26-29) P. intermedia/nigrescens (22-69) P. tannera (18-35) P. ruminicola (29) P. oris (39-67)	Fimbria Lipopolysaccharide Metabolites (indole, H2S,ammonia, acetic and succinic acids) Proteinases Hemolysins Acid phosphatase Phospholipase Heat-shock proteins	Pseudoramibacter alactolyticus G +/ An (50)	Unknown
	Campylobacter spp. G -/ M C. rectus (80) C. gracilis (30)	Extracellular cytotoxin Lipopolysaccharide S-layer Arylsulfatase H2S Heat-shock proteins	Propionibacterium spp G +/ F P. propionicum (52) P. acnes (27-52) P. acidifaciens (14)	Biofilm formation Lipase
	Dialister spp. G -/ An D. pneumosintes (48-78) D. invisus (53)	Unknown	Pseudomonas aeruginosa G -/ A (48)	Cell–cell signalling Protease profiles Biofilm
	Streptococcus spp. G +/ F S. milleri (31-50) S. constellatus (20-35) S. intermedius (35)	Hyaluronidase Deoxyribonuclease Hydrolytic enzymes	Dialister spp. G -/ An D. pneumosintes (46) D. invisus (30)	Unknown
	Bacteroides spp. G -/ An Bacteroidetes clone X083 (36-60)	Lipopolysaccharide Capsular polysaccharide	Solobacterium moorei G +/ An (33-78)	Gelatin hydrolysis
	Peptostreptococcus spp. G +/ An P. anaerobius (53-64)	Capsular polysaccharide Synergistic interaction with Facultative organisms or other anaerobes	Pyramidobacter piscolens G -/ An (60)	Unknown
	Peptococcus spp. G +/ An (64)	Extracellular enzymes (DNase, RNase, coagulase, and hemolysins)	Bacteroidetes clone X083 (53)	See primary infection
	Lactobacillus spp. G +/ An (65)	Adhesion proteins Survive in acidic conditions	Fusobacterium nucleatum (24-40)	See primary infection
	Eggerthella lenta G +/ An (47)	Cardiac glycoside reductase (digoxin inactivation enzyme)	Peptostreptococcus stomatis‏ (43)	See primary infection
	Anaerococcus prevotii G +/ An (43)	Unknown	T. forsythia‏ (12)	See primary infection
	Gemella morbillorum G +/ F (30)	Same pathogenic mechanisms found in viridans streptococci	F. nucleatum‏ (33)	See primary infection
	Olsenella uli G +/ An (45)	Biofilm formation	Candida albicans (yeast) F (9)	Mannose-containing proteins Mannan Phospholipase Proteinases Hyaluronidase Acid phosphatase Chondroitin sulfatase Phospholipase Heat-shock proteins
	Eikenella corrodens G -/ F (38)	Biofilm formation
	Lachnospiracea spp. G +/ An L. clone 55A-34 (57) L. clone MCE7_60 (43)	Unknown
	Eubacterium spp. G +/ An E. clone BP1-89 (43) E. brachy (56)	Unknown
	Phocaeicola spp. G -/ An (100)	Unknown

Abbreviations: G -, gram negative; G +, gram positive; F, facultative anaerobic; An, anaerobic; A, aerobic; M, microaerophilic.