17: Bacteroides, Tannerella, Porphyromonas and Prevotella

Chapter 17 Bacteroides, Tannerella, Porphyromonas and Prevotella

The genera described in this chapter are obligately anaerobic, short Gram-negative rods or coccobacilli. Historically, only the Bacteroides genus was known, but the application of new taxonomic techniques has resulted in the definition of three additional genera: Tannerella, Porphyromonas and Prevotella. Together they comprise a substantial proportion of the microflora of the dental plaque, intestine and the female genital tract (Table 17.1):

Table 17.1 Anaerobic Gram-negative bacilli of clinical interest

Organism Main colonization sites
Bacteroides  
B. fragilis group Colon
B. fragilis  
B. ovatus  
B. vulgatus  
B. distasonis  
B. capillosus Colon, oropharynx
B. ureolyticus Oropharynx, intestine, genitourinary tract
Tannerella  
T. forsythia Oropharynx
Porphyromonas  
P. gingivalis Oropharynx
P. endodontalis Oropharynx
Prevotella  
P. intermedia Oropharynx
P. nigrescens Oropharynx
P. melaninogenica Oropharynx
P. loescheii Oropharynx
P. pallens Vagina, oropharynx
P. corporis Vagina, oropharynx

• Bacteroides spp. are mainly restricted to species found predominantly in the gut and are the most common agents of serious anaerobic infections; Bacteroides fragilis is the main pathogen.
• Tannerella spp. are black-pigmented, anaerobic rods, strongly implicated as a major pathogen of periodontal disease. Tannerella forsythia is frequently isolated with Porphyromonas gingivalis, indicating an ecological relationship between them.
• Porphyromonas spp. are asaccharolytic pigmented species and form part of the normal oral flora. They are agents of periodontal disease and hence considered as periodontopathic organisms.
• Prevotella spp. include saccharolytic oral and genitourinary species; some species are periodontopathic.

Collectively, Tannerella, Porphyromonas and Prevotella species are referred to as black-pigmented anaerobes, as some organisms from these genera form a characteristic brown or black pigment on blood agar (Fig. 17.1).

image

Fig. 17.1 Black-pigmented colonies of periodontopathogen Porphyromonas gingivalis on blood agar. The pigment is thought to be related to breakdown products of the blood.

Bacteroides

Bacteroides fragilis

Habitat and transmission

Bacteroides species are the most predominant flora in the intestine (1011 cells per gram of faeces), far outnumbering Escherichia coli. They cause serious anaerobic infections such as intra-abdominal sepsis, peritonitis, liver and brain abscesses, and wound infection.

Characteristics

Strictly anaerobic, Gram-negative, non-motile, non-sporing bacilli, but may appear pleomorphic. The polysaccharide capsule is an important virulence factor.

Culture and identification

These organisms have stringent growth requirements; they demonstrate slow growth on blood agar and appear as grey to opaque, translucent col/>

Related posts:

  1. 16: Vibrios, campylobacters and Wolinella
  2. 18: Fusobacteria, Leptotrichia and spirochaetes
  3. 11: Streptococci, staphylococci and micrococci
  4. 32: Microbiology of dental caries
  5. 26: Infections of the gastrointestinal tract
  6. 4: Viruses and prions

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Jan 4, 2015 | Posted by in General Dentistry | Comments Off on 17: Bacteroides, Tannerella, Porphyromonas and Prevotella

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