The normal flora of the oral cavity is diverse and includes over 350 cultivable species of bacteria. The most common gram positive cocci found are streptococci, including the mutans, salivarius, anginosus, and mitis groups. These bacteria preferentially colonize different sites in the oral cavity like the teeth, tongue, and cheeks. The composition of the normal flora is influenced by factors like age, sex, diet, and oral hygiene. Imbalances in the flora can lead to oral diseases such as dental caries.

1. SIBAR INSTITUTE OF DENTAL SCIENCES
DEPATMENT OF ORAL AND MAXILLOFACIAL
PATHOLOGY
ORAL FLORA AND ITS VIRULANCE
Dr. Sujatha .R ,
Post Graduate .
1

2. Introduction:
 In a healthy animal, the internal tissues, e.g. blood,
brain, muscle, etc., are normally free of
microorganisms.
surface tissues
oral mucous membrane skin
2

3.  The mixture of organisms regularly found at any
anatomical site is referred to as the normal flora.
 Researchers - "indigenous microbiota".
3

4. Normal flora:
• Normal flora refers to the populations of microorganisms
that inhabit the skin and the mucous membranes of normal
human body.
 Resident flora
Indigenous flora
Supplemental flora
 Transient flora
4

5. Oral flora
 Oral flora comprises a diverse array of organisms and
includes eubacteria, fungi, protozoa and possibly a viral
flora which persist from time to time.
 Bacteria – 350 cultivable species
 Oral bacteria classification
a. Gram-positive
b. Gram-negative
5

6.  Depending upon the effect of oxygen divided as:
Obligate aerobe
Micro aerophilic / Micro aerophilic strict anaerobe
Facultative anearobes
Strict obligate anaerobe
Capnophilic
6

7. Bacteria commonly found on the surfaces of the human body
Bacterium Skin Nose Pharnyx Mouth
Staphylococcu
++ ++ ++ ++
s epidermidis
Staphylococcu
+ + + +
s aureus
Streptococcus
++ ++
salivarius
Streptococcus
+ ++
mutans
Enterococcus
+/- +
faecalis
Streptococcus
+/- + +
pneumoniae
Streptococcus
+/- + +
pyogenes 7

8. Bacterium Skin Pharnyx Mouth
Neisseria sp. ++ +
Neisseria ++
meningitidis
+
Enterobacteriaceae
+/- + ++
(Escherichia coli)
Pseudomonas +
aeruginosa
Haemophilus +/- +
influenzae
8

9.  Association between Humans and the Normal flora
Not much known
dynamic interactions
mutualistic
 Some normal flora
parasitic
pathogenic
9

10. Tissue specificity:
Most members of the normal bacterial flora prefer to
colonize certain tissues and not others.
This “tissue specificity” is usually due to properties of both
the host and the bacterium.
1. Tissue tropism
essential nutrients
growth factors, suitable oxygen, pH
10

11. Lactobacillus acidophilus, informally known as "Doderlein's bacillus"
colonizes the vagina because glycogen is produced which provides the
bacteria with a source of sugar that they ferment to lactic acid
11

12. 2. Specific adherence
12

13. Bacterium Bacterial adhesion Attachment site
Streptococcus Cell-bound protein (M-
Pharyngeal epithelium
pyogenes protein)
Streptococcus Cell- bound protein
Pellicle of tooth
mutans (Glycosyl transferase)
Streptococcus Buccal epithelium of
Lipoteichoic acid
salivarius tongue
Streptococcus Cell-bound protein (choline-
Mucosal epithelium
pneumoniae binding protein)
Staphylococcus
Cell-bound protein Mucosal epithelium
aureus
Neisseria N-methylphenyl- alanine Urethral/cervical
gonorrhoeae pili epithelium
Enterotoxigenic
Type-1 fimbriae Intestinal epithelium
E. coli
13

14. 3. Biofilm formation:
Some of the indigenous bacteria are able to construct
biofilms on a tissue surface, or they are able to colonize a
biofilm built by another bacterial species.
Many biofilms are a mixture of microbes, although one
member is responsible for maintaining the biofilm and may
predominate.
14

15. Cartoon depicting biofilm formation.
15

16.  The classic biofilm - oral cavity
dental plaque on the teeth.
 Plaque is a naturally-constructed biofilm,
thickness of 300-500 cells - teeth.
16

17.  These accumulations subject the teeth and gingival
tissues to high concentrations of bacterial metabolites,
which result in dental diseases like caries.
17

18. The Composition of Normal flora
The makeup of the normal flora influenced
genetics
age
sex
stress
nutrition
and diet of the individual.
18

19.  Three developmental changes in humans ,weaning,
the eruption of the teeth, and the onset and cessation of
the ovarian functions, invariably affect the composition
of the normal flora in the oral cavity.
The Bacterial Flora of Humans
© 2007 Kenneth Todar University of Wisconsin-Madison
Department of Bacteriology
19

20. Table . Predominant bacteria at various anatomical locations in adults.
Anatomical Location Predominant bacteria
Skin staphylococci and corynebacteria
Conjunctiva sparse, Gram-positive cocci and
Gram-negative rods
Oral cavity
Teeth Streptococci, lactobacilli
mucous membranes Streptococci and lactic acid bacteria
Upper respiratory tract
nares (nasal membranes) staphylococci and corynebacteria
pharynx (throat) streptococci, neisseria, Gram-negative
rods and cocci
20

21. Normal Flora of the oral Cavity:
Various streptococci in a biofilm in the oral cavity.
21

22. Flora of the oral cavity:
GRAM POSITIVE COCCI:
Genus streptococcus:
Streptococcus mutans. Gram stain
22

23. The mutans group:
Main species Strep mutans, strep sorbinus,
strep cricetus
Cultural characteristics Mitis Salivarius Agar (MSA)
Intra oral sites Teeth
and
infections Dental caries
23

24. The salivarius group:
Main species Strep salivarius,
Strep vestibularis
Cultural characteristics Mitis Salivarius Agar (MSA)
Intra oral sites dorsum of the tongue
saliva.
and
infections does not cause major oral
pathogenesis
24

25. The anginosus group:
Main species Strep constellatus,
Strep intermedius,
Strep anginosus
Cultural characteristics Mitis Salivarius Agar (MSA).
Intra oral sites Gingival crevice
and
Dentoalveolar and endodontic
infections
infections.
25

26. The mitis group
Main species Strep mitis;
Strep sanguis
Strep gordonii
Strep oralis
Cultural characteristics Mitis Salivarius Agar (MSA).
Intra oral sites dental plaque biofilms , tongue
and cheek.
and
infections dental caries.
26

27. Anaerobic streptococci
Main species Micromonas micros
Finegoldia magnus
Cultural characteristics
Intra oral sites teeth, especially the carious
dentine.
and
infections periodontal and dentoalveolar
abscesses
27

28. Genus stomatococcus
Main species Stomatococcus
Cultural characteristics facultative anaerobes
Intra oral sites tongue and the gingival crevice.
and
infections major opportunistic pathogen
28

29. Genus stomatococcus
29

30. Genus Staphylococcus
Main species Staph aureus,
staph epidermidis,
Staph saprophyticus
Cultural characteristics blood agar
Intra oral sites Present on the buccal mucosa
and
infections Angular chelitis
30

31. Genus Staphylococcus
31

32. GRAM POSITIVE RODS AND FILAMENTS:
These organisms are very commonly isolated
from the biofilms of dental plaque.
This group consists of the following organisms –
Actinomycetes
Lactobacilli
Eubacteria
Propionibacteria.
32

33. Genus actinomycetes
Main species Actino israeli
Actino gerensceriae
Actino odontolyticus
Actino naeslundii
Cultural characteristics facultative anaerobes.
Intra oral sites
and
infections
33

34. Actinomycetes
34

35. Main intraoral sites and infections:
 They are seen on the gingiva, on the mucosal and also
on the teeth surfaces.
 Actinomyces odontolyticus is related to the earliest
stages of enamel demineralization and the progression of
small caries lesions.
 Actinomyces naeslundii has been related to root
surface caries and gingivitis.
35

36. Actinomyces israeli is an opportunistic pathogen
causing cervicofacial and ileocecal actinomycosis.
Actinomyces gerensceriae and Actinomyces georgiae
are considered to be the minor components of healthy
gingival flora.
36

37. Genus Lactobacillus -
Main species Lacto casei
Lacto fermentum
Lacto acidophilus
Lacto salivarius
Lacto rhamnosus.
Cultural characteristics Rogosa agar.
Intra oral sites dental plaque biofilm,
advancing front of dental caries
and
infections
37

38. Lactobacillus
38

39. Genus Eubacterium
Main species Eubact brachy
Eubact nodatum
Eubact saphenum
Eubact yurii.
Cultural characteristics Obligate anaerobes
Intra oral sites Dental plaque biofilm, calculus
and
Periodontal disease
infections
Eubacterium yurii is involved in
the “corn-cob” formation in the
dental plaque
39

40. Rod shaped eubacterium
40

41. Genus propionibacterium
Main species Propionibacterium acnes
Cultural characteristics
Strict anaerobes
Intra oral sites gingival pockets and plaque
biofilms
and
infections root surface caries
41

42. OTHER NOTABLE GRAM-POSITIVE ORGANISMS:
• Rothia dentocariosa - Gram-positive branching filament -
strict aerobe
Found in plaque & isolated from patients with infective
endocarditis.
• Bifidobacterium dentium - Gram-positive, strict anaerobe,
Regularly isolated from the biofilms of plaque, and its role in
disease is unclear.
42

43. GRAM-NEGATIVE COCCI
43

44. Genus Nisseria
Main species Neisseria subflava
Neisseria mucosa
Neisseria sicca
Cultural characteristics facultative anaerobes
Intra oral sites tongue, saliva, oral mucosa and
early plaque.
and
infections rarely associated with any oral
disease.
44

45. Neisseria
45

46. Genus Veillonella
Main species Veillonella parvula
Veillonella dispar
Veillonella atypical
Cultural characteristics Rogosa vancomycin agar
Intra oral sites tongue, saliva, plaque biofilm.
and not associated with any oral
disease.
infections
46

47. GRAM-NEGATIVE RODS – FACULTATIVE
ANAEROBIC AND CAPNOPHILIC GENERA
47

48. Genus Haemophilus
Gram-negative coccobacilli
Main species Haemophilusparainfluenzae
Haemophilus segnis
Haemophilus aphrophilus
Haemophilus haemolyticus
Cultural characteristics Facultative anaerobes
Intra oral sites tongue, saliva, plaque biofilm.
and
dentoalveolar infections, acute
infections sialadenitis, and infective
endocarditis
48

49. Genus Actinobacillus
Main species Actinobacillus
actinomycetemcomitans
Cultural characteristics
Intra oral sites
and
infections
49

50. Culture characteristics:
The freshly isolated strains contain fimbriae that are lost
on subculture.
Actinobacillus produces many virulence factors like –
leukotoxin; epitheliotoxin; collagenase; protease that
cleaves immunoglobulin G (IgG).
50

51. microscopic picture of Actinobacillus
51

52. Main intraoral sites and infections:
Mostly seen in the periodontal pockets.
 They are implicated in aggressive forms of periodontal
disease (e.g. localized and generalized forms of aggressive
periodontitis)
 They are often isolated as co-pathogens from the
cervicofacial Actinomyces infections.
52

53. Genus Eikenella
Gram negative coccobacilli
Main species Eikenella corrodens
Cultural characteristics blood agar
Intra oral sites plaque biofilms
and
infections chronic periodontitis
dentoalveolar abscesses
53

54. Genus Capnocytophaga
Gram-negative fusiform rods
Main species Capnocytophaga gingivalis
C. Sputigena
C. Ochracea
C. Granulose
C. Haemolytica
Cultural characteristics Capnophilic organisms
Intra oral sites Plaque, mucosal surfaces,
saliva.
and
infections Periodontal disease
54

55. GRAM-NEGATIVE RODS – OBLIGATE ANAEROBIC
GENERA:
Form large portion of the plaque biofilms
55

56. Genus Porphyromonas
Main species Porphyromonas gingivalis
P. Endodontalis
P. Catoniae
Cultural characteristics Strict anaerobes
Intra oral sites Gingival crevice and the
subgingival plaque
and
infections chronic periodontitis and
dentoalveolar abscess.
56

57. Porphyromonas
57

58. Genus Fusobacterium
Gram-negative rods
Main species Fusobacterium nucleatum
F. Alocis
F. Sulci
F. periodonticum.
Cultural characteristics Strict anaerobes
Intra oral sites Normal gingival crevice, tonsils
and
infections acute ulcerative gingivitis,
halitosis
58

59. SEM picture of Fusobacterium
59

60. Genus Treponema
Main species Treponema denticola
Treponema macrodentium
Treponema skoliodontium
Treponema sokranskii
Treponema maltophilum
Cultural characteristics Strict anaerobes
Intra oral sites Gingival crevice
and
acute ulcerative gingivitis,
infections destructive periodontal disease
60

61. ORAL PROTOZOA:
Genus Entamoeba
Main species Entamoeba gingivalis
Cultural characteristics Strict anaerobes
Intra oral sites
and
Periodontal disease
infections
61

62. Genus Trichomonas
Main species Trichomonas tenax
Cultural characteristics Strict anaerobes
Intra oral sites Gingival crevice
and
infections Unclear
62

63. Beneficial effects of the normal flora:
1.Can synthesize and excrete vitamins
2.Prevent colonization by pathogens
3.May antagonize other flora
4.Stimulate the production of natural antibodies
63

64. OBLIGATORY PARASITES
WHICH CAN BE
COMMENSALS IN THE ORAL
CAVITY
64

65. MYCOPLASMAS
Main species Mycoplasma pneumoniae
Mycoplasma buccale
Mycoplasma oral
Mycoplasma salivarium;
Mycoplasma faucium
Cultural characteristics Special agar and broth media
Intra oral sites oro-pharyngeal region, saliva, dental
plaque
and
infections Mucocutaneous lesions
65

66. FUNGI
Yeasts
Main species Cryptococcus
Rhodotorula
Intra oral sites Mucosa
and
infections Mucosal ulcers in
immunocompramised patients
66

67. Yeast-like fungi
genus Candida
Main species Candida albicans
Candida tropicalis
Candida krusei
Candida glabrata
Candida guillermondii
Candida parapsilosis
Candida kefyr
Intra oral sites Mucosa
and
infections Mucosal ulcers in
immunocompramised patients
67

68. Virulence:
The degree of pathogenicity of a microorganism as indicated
by the severity of disease produced and the ability to invade
the tissue of the host ; by extension, the competence of any
infectious agent to produce pathologic effects.
( Dorland’s Medical Dictionary)
68

69. The main etiological agent of periodontal disease is microflora
– dental plaque
Dental plaque:
It is defined as a structured, resilient, yellow-grayish substance
that adheres to the intraoral hard surfaces, including removable
and fixed restorations.
69

70. Composition
Bacteria (matrix of salivary glycoproteins & extra
cellular poysaccharides)
1 gm = 10 11 bacteria
> 500 species
30% uncultivable species
70

71. Dental plaque
Supra gingival plaque:
Demonstrates a multi-layered accumulation of
bacterial morphotypes
gram positive cocci + rods - tooth surface
gram negative rods, filaments - outer surface
Sub-gingival bacteria
anerobic bacteria
71

72. Plaque formation of at the ultra-structural level
Saliva derived layer – acquired pellicle
- glycoproteins, proline-rich proteins
Streptococcus & Actinomycetes bind to specific
salivary proteins
Veillonellae, Capnocytophagae, Prevotella – bind to
Streptococci, Actinomycetes
Primary colonizers
Secondary colonizers
72

73. Microorganisms associated with periodontal disease:
Bacteria associated –
gram +ve
Streptococcus( s.sanguis, s.mitis)
Actinomycetes (A.viscosus, A.naeslendi)
gram –ve
capnocytophage
neisseria
73

74. The currently recognized key Gram negative
periodontopathogens include:
Porphyromonas gingivalis (P.g),
Prevotella intermedia (P.i),
Bacteroides forsythus (B.f),
Aggregatibacter actinomycetemcomitans (A.a),
Fusobacteriumnucleatum (F.n),
Capnocytophaga species(C.sp),
Campylobacter rectus (C.r)
74

75. Porphyromonas gingivalis
previously known as Bacteroides
strictly anaerobic, Gram negative
Virulence mechanism:
carbohydrate capsule – prevents opsonization
Virulence factors:
fimbriae - adhesion
proteases – degrade collagen fibers, cytotoxins
hemolysin
75

76. Actinobacillus actinomycetemcomitans
Gram –ve
Virulence factors:
leukotoxin
forms pores – death – osmotic pressure
collagenase
destruction of connective tissue
lipopolysaccharides
macrophages – IL 1, IL2 – bone resorption
Microbial etiology of periodontal disease – a mini review
Medicine and Biology Vol.15, No 1, 2008 - Ljiljana Kesic 76

77. Fusobacterium nucleatum
Virulence factors:
induce – apoptotic cell death – PMN
release – cytokines
As fusobacterium co-aggregates with most oral
microorganisms – binding organisms
Microbial etiology of periodontal disease – a mini review
Medicine and Biology Vol.15, No 1, 2008 - Ljiljana Kesic
77

78. Capnocytophaga sp
Gram –ve
Vrulence:
lipopolysaccharides – activity on alveolar bone
proteolytic enzymes
78

79. Spirochetes:
Motile, flagella
Treponema denticola
Treponema vincentii
• a lipopolysaccharide, and unusual metabolic endproducts,
like indole, hydrogen sulphide, ammonia, which are
potentially toxic to host cells.
• T.d – proteolytic enzyme – destroy (IgA, IgM, Ig G)
79

80. Dental caries
Multifactorial
80

81. Virulence factors:
 Specific adherence to tooth surface using antigen
I/II adhesin and GTF (glycosyl transferase )
 Production of extracellular polysaccharides
(dextran) allows the cariogenic bacteria to stick onto
the teeth and form a biofilm.
 acid-tolerance (aciduricity)
 Able to maintain microbial growth and continue
acid production at low pH values.
81

82.  Rapid metabolism of sugars to lactic and other
organic acids
 Lower the pH to below 5.5, the critical pH. Drives
the dissolution of calcium phosphate (hydroxyapatite)
of the tooth enamel (acidogenicity)
 Accumulation of intracellular polysaccharides
(carbon/energy reserve) 82

83. Virulence properties
streptococus mutans
Adhesion
sucrose – independent adhesion
sucrose – dependent adhesion
Acidogenicity
Acid-tolerance
83

84. Adhesion
Sucrose – independent adhesion
• influenced by antigen I/II
• proteins of this family share structural similarity
• role of antigen I/II
adhesion of s. mutans to saliva – coated
hydroxyapetite
Ohat et al : characterization of a cell – surface protein
antigen of hydrophilic streptococcus mutans strain.
J Gen Microbiology 135, 981-988
84

85. Gram stain - streptococcus
85

86. Interaction between antigen I/II & salivary components
alanine- rich & proline-rich domains
Proved - mutant lacking P1 ( antigen I/II)
- did not bind
Bowen et al : Role of a cell surface-associated protein in
adherence and dental caries . Infect immunology 59,
4606-4609
86

87. Sucrose-Dependent Adhesion
• The action of glucosyltransferases (GTFs) in the synthesis
of glucans is the major mechanism behind sucrose -
dependent adhesion.
• GTFs – sucrase activity
• sucrose glucose + fructose
added
growing polymer of glucan
87

88. s.mutans - 3 GTFs -
encoded by gftb, gftc, gftd
So , GTFs – synthesize
Water- soluble glucan water- insoluble glucan
(dextran) (mutan)
88

89. • The ability of glucan to facilitate adhesion of S.mutans
may be due to hydrogen bonding of the glucan polymers to
both the salivary pellicle and the bacteria.
• This glucan could be synthesized by extracellular GTFs
that bound the salivary pellicle, S. mutans that had
previously adhered via sucrose-independent means, or
perhaps by other oral streptococci.
89

90. • It is not known why S. mutans requires multiple GTFs,
but there is evidence that the different GTFs have
differing affinities for the bacterial surface or salivary
pellicle , and that a particular ratio of each is necessary
for optimal sucrose-dependent adhesion.
Ooshima et al: contbutions of three glucosyltransferases
to sucrose-dependent adherence of streptococcus
mutans. J dental res :80 , 1672-1677
90

91. • Another possibility - WapA ( antigen A)
its yet uncertain
• Carbohydrate Metabolism:
additional putative factors
Gene product Hypothesized function
Ftf Catalize the synthesize of
fructans
FruA Breakdown fructans for
energy
DexA Glucan synthesis
91

92. Acidogenicity:
S.mutans
lactate, formate, acetate, ethanol
( fermentation end-products)
Glucose
92

93. •The velocity with which S. mutans produces acid when
tested at a pH in the range from 7.0 to 5.0 exceeds that of
other oral streptococci in most instances.
Soet, J.J., B. Nyvad, & M. Kilian: Strain-related
acid production by oral streptococci. Caries Res 34, 486-
490, (2000)
• The acidogenicity of s.mutans---- ecological changes
in the plaque flora that includes an increase in
proportion of s.mutans
93

94. Acid – tolerance
• Growth-inhibitory pH
• distinguish s.mutans
• this is largely mediated by
- F1F0 – ATPase ATR
- gene and protein expression
• acid – tolerance may be aided by the synthesis of
water-insoluble glucan and the formation of biofilm
94

95. • s.mutans with in biofilm – outside
ATR , physical characteristics of the biofilm
95

96. The role of lactobaccillli:
 Absent – incipient lesions
 Pioneer organisms in the advancing front of carious
process
Virulence :
synthesize sucrose
their ability to grow low- pH  lactic acid
The exact role – not well defined
96

97. The results of this study suggest that Lactobacilli colonizes
sites in the oral cavity (including the tongue and saliva)
other than the tooth surface in rats.
The effect of Lactobacilli in plaque toward reduction of S.
mutans-induced dental caries in rats
Oral Ecology and Virulence of Lactobacillus casei and Streptococcus
mutans in Gnotobiotic Rats : SUZANNE M. MICHALEK el al
Department ofMicrobiology and Institute of Dental Research, The
University ofAlabama in Birmingham, Birmingham, Alabama 3529
97

98. Candidiasis:
The physiological state host – etiology
Virulence factors:
hyphal formation,
surface recognition molecules,
extracellular hydrolytic enzyme production
98

99. Hydrolytic enzymes:
production – proteinases
CATALIZE
hydrolysis of peptide bonds in proteins
secreated aspartyl proteinase (SAP genes)
99

100. Correlation between Sap Production In Vitro and Candida
Virulence
Main focus points.
(i) The virulence of C. albicans species appears to correlate
with the level of Sap activity in vitro and may correlate with
the number of SAP genes.
(ii) Infected patients (oral or vaginal) harbor C. albicans
strains that are significantly more proteolytic than are
isolates from asymptomatic carriers.
. 100

101. (iii) HIV infection appears to lead to the selection of C.
albicans strains with heightened virulence attributes such
as proteinase production
101

102. Association of Sap Production with Other Virulence
Processes of C. albicans
Main focus points.
(i) Sap proteins facilitate C. albicans adherence to
many host tissues and cell types.
(ii) Hypha formation and SAP4 to SAP6 expression are
coordinately regulated, but the signaling pathways
remain to be elucidated.
102

103. (iii) SAP1 appears to be regulated by phenotypic
switching, but the contribution of switching to C. albicans
virulence in vivo is not yet clear.
103

104. How do Sap proteins contribute to adherence?
 Not clear
 Two hypothesis
i. C. albicans proteinases could act as ligands to
surface moieties on host cells, which does not necessarily
require activity of the enzymes.
ii. C. albicans utilizes Sap proteins as active
enzymes to modify target proteins or ligands on the fungal
surface or on host cells (i.e., epithelial cells), which may
alter surface hydrophobicity or lead to conformational
changes, thus allowing better adhesion of the fungus 104

105. Candida albicans Secreted Aspartyl Proteinases in
Virulence and Pathogenesis
Julian R. Naglik et al; Microbiology and Molecular
biology
105

106. THANK YOU
106