Significance of the Biofilm
Environment
• Studies of oral microbial communities as biofilms in
vitro further highlight the significance of structural
and physiologic interactions between bacterial species
in plaque.
• Recent analyses of more than 13,000 plaque samples
of 40 subgingival microorganisms using a DNAhybridization methodology was used to define
“complexes” of periodontal microorganisms.
• The composition of the different complexes is based
on the frequency with which microorganisms are
recovered together. Interestingly, the early colonizers
are either independent of defined complexes (A.
naeslundii, A. viscosus) or members of the yellow
(Streptococcus spp.) or purple complexes (A.
odontolyticus)
• The microorganisms primarily considered secondary
colonizers fell into the green, orange or red complexes.
• The Green complex includes E. corrodens,
Actinobacillus actinomycetemcomitans serotype a,
and Capnocytophaga spp.
• The Orange complex includes Fusobacterium,
Prevotella, and Campylobacter spp. The green and
orange complexes include species recognized as
pathogens in periodontal and nonperiodontal infections.
• The Red complex consists of P. gingivalis, B.
forsythus, and T. denticola. The red complex is of
particular interest because it is associated with
bleeding on probing, which is an important clinical
parameter of destructive periodontal diseases.
ASSOCIATION OF PLAQUE
MICROORGANISMS WITH
PERIODONTAL DISEASES
Microbial Specificity of Periodontal Diseases
• In the mid-1900s, periodontal disease was believed
to result from an accumulation of plaque over time
in conjunction with a diminished host response and
increased host susceptibility with age.
• However, several observations contradicted these
conclusions.
First,
some
individuals
with
considerable amounts of plaque and calculus, as well
as gingivitis, never developed destructive
periodontitis.
Nonspecific Plaque Hypothesis
• The nonspecific plaque hypothesis maintains that
periodontal disease results from the “elaboration
of noxious products by the entire plaque flora.”
• According to this thinking, small amounts of plaque
are present, the noxious products are neutralized by
the host. Similarly, large amounts of plaque would
produce large amounts of noxious products, which
would essentially overwhelm the host's defenses.
Inherent in the nonspecific plaque hypothesis is the
concept that control of periodontal disease depends
on control of the amount of plaque accumulation.
Specific Plaque Hypothesis
• The specific plaque hypothesis states that only certain
plaque is pathogenic, and its pathogenicity depends
on the presence of or increase in specific
microorganisms.
• Acceptance of the specific plaque hypothesis was
spurred
by
the
recognition
of
A.
actinomycetemcomitans as a pathogen in localized
aggressive periodontitis. These advances led to a
series of association studies focused on identifying
specific periodontal pathogens by examining the
microbiota associated with states of health and
disease in cross-sectional and longitudinal studies.
Microorganisms Associated with
Specific Periodontal Diseases
• The microbiota associated with periodontal health
and disease has been studied with a wide variety of
techniques for sampling, cultivation, and/or
detection of bacteria by DNA hybridization.
• Further, the classification of periodontal diseases has
undergone a number of changes during the time that
association studies have been conducted.
•
Early studies that used appropriate microbiologic
procedures clearly demonstrated that:
1. number and proportions of different subgingival
bacterial groups varied in periodontal health when
compared with the disease state.
2. The total number of bacteria, determined by
microscopic counts per gram of plaque, are twice as
high in periodontally diseased sites than in healthy
sites
3. more plaque is found at diseased sites, this suggests
that the total bacterial load is much greater than that
at healthy sites.
• The differences between periodontal health and disease also
are evident :
• Fewer coccal cells and more motile rods and spirochetes
are found in diseased sites than in healthy sites
• The bacteria cultivated from periodontally healthy sites
consist predominantly of gram-positive facultative rods
and cocci (approximately 75%), While gingivitis (44%)
and periodontitis (10% to 13%).
• These decreases are accompanied by increases in the
proportions of gram-negative rods, from 13% in health to
40% in gingivitis and 74% in advanced periodontitis
Periodontal Health
• The bacteria associated with periodontal health are
primarily gram-positive facultative species and
members of the genera Streptococcus and
Actinomyces (e.g., S. sanguis, S. mitis, A. viscosus,
and A. naeslundii).
• Small proportions of gram-negative species are also
found, most frequently P. intermedia, F. nucleatum,
and Capnocytophaga, Neisseria, and Veillonella
spp.
• Microscopic studies indicate that a few spirochetes
and motile rods also may be found.
• S. sanguis, Veillonella parvula, and C. Ochracea.
These species probably function in preventing the
colonization or proliferation of pathogenic
microorganisms.
Gingivitis
• After 8 hours without oral hygiene, bacteria may be
found at concentrations of 103 to 104 per square
millimeter of tooth surface and will increase in
number by a factor of 100 to 1000 in the next 24-hour
period.
• The initial microbiota of experimental gingivitis
consists of gram-positive rods, gram-positive cocci,
and gram-negative cocci. The transition to gingivitis
is evident by inflammatory changes observed in the
gingival tissues and is accompanied first by the
appearance of gram-negative rods and filaments,
then by spirochetal and motile microorganisms.
• The bacteria found in naturally occurring dental
plaque-induced gingivitis (chronic gingivitis) consist
of roughly equal proportions of gram-positive (56%)
and gram-negative (44%) species, as well as
facultative
(59%)
and
anaerobic
(41%)
microorganisms.
• Predominant gram-positive species include S.
sanguis, S. mitis, S. intermedius, S. oralis, A.
viscosus, A. naeslundii, and Peptostreptococcus
micros.
• The
gram-negative
microorganisms
are
predominantly F. nucleatum, P. intermedia, V.
parvula, as well as Hemophilus, Capnocytophaga and
Campylobacter spp
• Pregnancy-associated gingivitis is an acute
inflammation of the gingival tissues associated with
pregnancy. This condition is accompanied by
increases in steroid hormones in crevicular fluid and
dramatic increases in the levels of P. intermedia,
which use the steroids as growth factors.
• Studies of gingivitis support the conclusion that
disease development is associated with selected
alterations in the microbial composition of dental
plaque and are not simply the result of an
accumulation of plaque.
Chronic Periodontitis
• The hallmark of periodontitis is the loss of connective
tissue attachment to the tooth.
• Microscopic examination of plaque from sites with
chronic periodontitis have consistently revealed
elevated proportions of spirochetes.
• high percentages of anaerobic (90%) gram-negative
(75%) bacterial species.
• In chronic periodontitis, the bacteria most often
cultivated at high levels include P. gingivalis, B.
forsythus, P. intermedia, C. rectus, Eikenella
corrodens,
F.
nucleatum,
A.
actinomycetemcomitans,
P.
micros,
and
Treponema and Eubacterium spp.
• C. rectus, P. gingivalis, P. intermedia, F. nucleatum,
and B. forsythus were found to be elevated in the
active sites.
• Furthermore, detectable levels of P. gingivalis, P.
intermedia, B. forsythus, C. rectus, and A.
actinomycetemcomitans are associated with
disease progression.
• Both P. gingivalis and A. actinomycetemcomitans have been
shown to invade host tissue cells, which may be significant in
aggressive forms of adult periodontitis.
• Recent studies have documented an association between
chronic periodontitis and viral microorganisms of the
herpesviruses group, most notably Epstein-Barr Virus-1
(EBV-1) and human cytomegalovirus (HCMV).
• Further, the presence of subgingival EBV-1 and HCMV are
associated with high levels of putative bacterial pathogens,
including P. gingivalis, B. forsythus, P. intermedia, and T.
denticola.
Localized Aggressive Periodontitis.
• The microbiota associated with localized aggressive
periodontitis is predominantly composed of gram-negative,
capnophilic, and anaerobic rods.
• Microbiologic studies indicate that almost all LJP sites harbor
A. actinomycetemcomitans, which may comprise as much as
90% of the total cultivable microbiota.
• Other organisms found in significant levels include P.
gingivalis, E. corrodens, C. rectus, F. nucleatum, B.
capillus, Eubacterium brachy, and Capnocytophaga spp.
and spirochetes.
• Herpesviruses, including EBV-1 and HCMV, also have been
associated with localized aggressive periodontitis.
Periodontitis as a Manifestation of
Systemic Disease.
• This is consistent with the concept that the occurrence
of severe destruction at an early age is a reflection of
an increased host susceptibility, in this case
resulting from systemic disease. Identification of
severe periodontal destruction in a child may be one
of the first signs of systemic disease.
Necrotizing Periodontal Diseases.
• Necrotizing periodontal diseases present as acute
inflammation of the gingival and periodontal tissues
characterized by necrosis of the marginal gingival
tissue and interdental papillae. Clinically, these
conditions often are associated with stress or
human immunodeficiency virus (HIV) infection.
• Microbiologic studies indicate that high levels of P.
intermedia and spirochetes are found in
necrotizing ulcerative gingivitis lesions.
• Spirochetes are found to penetrate necrotic tissue
and apparently unaffected connective tissue.
Abscesses of the Periodontium.
• They often occur in patients with untreated periodontitis but
also may be found in patients during maintenance or after
scaling and root planing.
• Typical clinical symptoms of periodontal abscesses include
pain, swelling, bleeding on probing, and mobility of the
involved tooth.
• Signs of systemic involvement may be present, including
cervical lymphadenopathy and an elevated white blood cell
count.
• Investigations reveal that bacteria recognized as periodontal
pathogens are commonly found in significant numbers in
periodontal abscesses. These microorganisms include F.
nucleatum, P. intermedia, P. gingivalis, P. micros, and B.
forsythus.
Conclusions from Studies of the
Association of Microorganisms
with Periodontal Diseases
• The periodontal microbiota is a very complex ecologic system
with many structural and physiologic interactions among the
resident bacteria and between the bacteria and the host.
•
It is clearly possible that levels of a particular species may be
elevated as a result of environmental changes produced by the
disease process and may not be a causative agent.
• A possible example of this comes from studies on the
development of gingivitis in humans at the time of puberty. It
was found that the proportions of Capnocytophaga spp.
increased before the development of gingivitis, whereas P.
intermedia was recovered after the onset of gingivitis.
• This suggests a causative role for the Capnocytophaga spp., in
contrast to the emergence of P. intermedia associated with
environmental changes upon the development of gingivitis.
CRITERIA FOR IDENTIFICATION
OF PERIODONTAL PATHOGENS
• In the 1870s, Robert Koch developed the classic
criteria by which a microorganism can be judged to
be a causative agent in human infections. These
criteria, known as Koch's postulates, stipulate that the
causative agent must:
1. Be routinely isolated from diseased individuals
2. Be grown in pure culture in the laboratory
3. Produce a similar disease when inoculated into
susceptible laboratory animals
4. Be recovered from lesions in a diseased laboratory
animal
• Sigmund Socransky, a researcher at the Forsyth Dental Center
in Boston, proposed criteria by which periodontal
microorganisms may be judged to be potential pathogens.
According to these criteria, a potential pathogen must:
1. Be associated with disease, as evident by increases in the
number of organisms at diseased sites
2. Be eliminated or decreased in sites that demonstrate clinical
resolution of disease with treatment
3. Demonstrate a host response, in the form of an alteration in the
host cellular or humoral immune response
4. Be capable of causing disease in experimental animal models
5. Demonstrate virulence factors responsible for enabling the
microorganism to cause destruction of the periodontal tissues
FUTURE ADVANCES IN
PERIODONTAL MICROBIOLOGY
•
DNA-based methodology for the identification and detection
of specific bacteria and viruses represents a remarkable
advantage in time and cost as compared with cultivation
techniques. This has led to a dramatic increase in the number
of samples that can be examined and the number of
microorganisms enumerated. Perhaps even more profound, the
ability to detect microorganisms that cannot be cultivated has
underscored the limitations of our knowledge of this complex
ecologic niche. The use of these approaches to continue the
study of the periodontal region will undoubtedly refine our
current understanding of the microbial ecology and etiology of
diseases.
ANY QUESTIONS ?