Bacterial Flora in
Human Oral Cavity
Made by
Luan Yijun, Zhang Yanhui, Liu Junying,
Li Na, Xuxia, Liu Song, Wang Ge,
Zhang Tianqi, Ying Wanggui,
Li Shengfeng
1.Normal flora in human oral cavity
2.Several dental diseases caused by
bacteria
3.What can we do to prevent dental
disease
 The human mouth is home to more than 500
species of bacteria.
 Oral bacteria include streptococci,
lactobacilli, staphylococci and
corynebacteria(棒状杆菌), with a great
number of anaerobes, especially
bacteroides(类杆菌).
Normal flora changes with age
 At birth the oral
cavity is sterile
 It rapidly becomes
colonized from the
environment
 Streptococcus salivarius is dominant and
may make up 98% of the total oral flora until
the appearance of the teeth (6 - 9 months in
humans)
 The eruption of the teeth during the first year
leads to colonization by S. mutans（变形链
球菌） and S. sanguis ,they will persist as
long as teeth remain
 Other strains of streptococci adhere strongly
to the gums（牙龈） and cheeks but not to
the teeth
 The creation of the gingival crevice（齿龈裂
缝） area increases the habitat for the
variety of anaerobic species found
 Bacteroides and
spirochetes
colonize around
puberty
Functions of normal flora
 occupy available colonization sites
 contribute to host nutrition
 contribute to immunity
 exert microbial antagonism against
heterogenous species
 Since some of these bacteria are
parasites or opportunistic pathogens, if
they invade tissues not normally
accessible to them, characteristic
diseases result
back
 Dental Plaque （牙菌斑）
 Dental Caries （龋齿）
 Periodontal Disease （牙周病）
Dental Plaque
 material adhering to the teeth, consists of
bacterial cells (60-70% the volume of the
plaque), salivary polymers, and bacterial
extracellular products
 Streptococcus sanguis and Streptococcus
mutans
Mechanism
a weak attachment of the streptococcal cells to
salivary glycoproteins →a pellicle on the surface
of the teeth → a stronger attachment →
( glycosyl transferase, an enzyme on the cell
surface of Streptococcus mutans, is apparently
involved in initial attachment of the bacterial cells
to the tooth surface and ) → conversion of
Sucrose (蔗糖）to dextran（右旋糖酐） and
levan（左旋糖酐） polymers → form the
extracellular matrix of plaque
back
Dental Caries
 the destruction of the enamel（釉质）,
dentin（牙质）or cementum（牙骨质）
of teeth due to bacterial activities
 Streptococcus mutans, Lactobacilli，
Actinomyces（放线菌）, and various
proteolytic bacteria
Physiological and Biochemical
Properties of Streptococcus mutans
 a regular component of the normal oral flora of
humans
 contains the enzyme glycosyl transferase
 produces lactic acid, produces more lactic acid
and is more acid-tolerant than most other
streptococci
 stores polysaccharides made from dietary sugars,
can be utilized as reserve carbon and energy
sources for production of lactic acid
back
Periodontal Disease
 bacterial infections that affect the supporting
structures of the teeth (gingiva, cementum（
牙骨质）, periodontal membrane and
alveolar bone)
 Actinomyces, streptococci, spirochetes and
Bacteroides
 The mechanisms of tissue
destruction in periodontal disease
are not clearly defined but
hydrolytic enzymes, endotoxins,
and other toxic bacterial
metabolites seem to be involved
back
How to prevent dental diseases
 Brush your teeth two times
everyday, after arousing and
before sleeping
 Use toothpastes which
contains fluoride
 Use dental floss to clean
your teeth-gaps everyday