Characteristics of Veillonella

• Veillonella are anaerobic Gram Negative cocci
• Size: 0.3-0.5 µm in diameter
• Arrangement: found in pairs, cluster or in short chains
• The genus Veillonella is sub divided into 8 species, four of which have been isolated from human. The species includes parvula, V. atypical, V. dispar and V. montpellierensis.
• parvula is most frequently been associated with human infection
• This bacterium is well known for its lactate fermenting ability.

Habitat:

• Veillonella forms part of normal flora of intestine and oral mucosa of mammals.
• They are found in greatest concentration in saliva and on the dorsum of tongue.
• Also present on the mucosal surfaces and in the saliva of edentulous infants.

Cultural characteristics, Growth requirements and Metabolism:

• Veillonella are anaerobic non-spore forming and non-motile organisms.
• Optimum growth is obtained at 30-37°C, poor growth at 40°C and no growth above 45°
• They are Oxidase negative and catalase negative
• Human species of Veillonella do not ferment carbohydrate. They uses organic acid by-products of carbohydrates for metabolism. Lactate is the main source of energy that is converted to propionic acid along with acetic acid with release of CO2 and H2O.

Clinical significance of Veillonella:

• The role of Veilonella as a pathogen is unclear. Very little is known about virulence mechanisms of the organism.
• Veilonella have a gram negative cell wall containing lipopopysaccharide (LPS) with endotoxin activity. This LPS has been regarded as the major virulence factor in some disease causing Veilonella
• Some more pathogenic microbes such as Streptococcus mutans uses the biofilm formed by Veillonella parvula could be indirectly involved with pathogenesis.
• In human Veillonella parvula have been rarely implicated in cases of osteomyelitis and endocarditis
• In intravascular drug users, Veillonella has been associated with polymicrobial endocarditis.
• Occasionally veillonella has been isolated from sites of infection such as abscesses, pneumonia, sinusitis where they are typically part of a mixed culture.

Lab diagnosis of Veillonella:

1. Specimens:

• Specimens depends upon sites of infection
• Blood, Pus from abscess, pulmonary secretions etc

2. Direct microscopy:

• Gram staining; it revels very small gram negative cocci in clumps, pairs or short chain

3. Culture:

• Veillonella spp grow in enriched blood containing media such as brain-heart infusion agar and trypticase soya agar supplemented with sheep blood
• They produce small, round colonies with raised centers ranging from 0.5-1 mm in diameter
• The colonies have a grey green appearance on blood containing media
• No hemolysis is seen in blood agar
• Veillonella spp are non-fermentative and produce acetic acid and propionic acids.
• Veillonella spp are identified by following characteristics;
  • Requirement of anaerobiosis
  • Gram negative on Gram staining
  • Fermentation of lactate with production of propionic acid
  • Do not ferment glucose
  • Reduction of nitrate into nitrite; (performed by disc test)

Treatment of Veillonella infection:

• Veillonella spp are resistant to penicillin which is attributed to altered penicillin binding proteins.
• They are also resistant to vancomycin, ciprofloxacin and tetracycline.
• Chloramphenicol, clindamycin, metronidazole, meropenem, imipenem,piperacillin, cefoxitin are sensitive drug against Veillonella

Veillonella: Characteristics, Culture, clinical significance, lab diagnosis and treatment

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