Biological properties and taxonomy
Among all anaerobic gram-negative cocci, the genus Veillonella is of the greatest relevance to clinical medicine. In human pathology, the most frequently encountered clinically significant species are V. atypica, V. dispar, and V. parvula.
Morphologically, they are gram-negative coccoid bacteria. In a microscopic smear, the cells are usually arranged in pairs (as diplococci), in short chains, or, somewhat less frequently, singly. Externally and in their arrangement, these microorganisms bear a marked resemblance to Neisseria, which is important to consider during initial microscopy. Key morphological features of veillonellas are that they are strictly non-motile and never form a capsule.
From the perspective of cultural and biochemical properties, these bacteria are quite fastidious regarding growth conditions. They are capable of growing exclusively on complex nutrient media under strict anaerobic conditions. A feature of their metabolism is that during life activity they actively release carbon dioxide ($CO_2$), and some specific species are able to produce porphyrins.
Ecology and mechanisms of infection development
Veillonellas are natural inhabitants of the human body and are part of the normal microflora. Their most typical localization sites are the mucous membranes of the oral cavity and nasopharynx. In addition, it is hypothesized that they may also be present in the gut microbiome.
Despite being members of the normal flora, upon a decrease in the body's resistance they are capable of causing various purulent-inflammatory processes. The main feature of the pathogenesis of infections caused by anaerobic cocci lies in the nature of the inflammation itself. These microorganisms extremely rarely act as the sole causative agent of the disease (monoinfection is atypical for them). On the contrary, they predominantly form part of polymicrobial associations, developing jointly with other aerobic and anaerobic bacteria. Thus, they are classical participants in mixed infections, worsening their course.
Laboratory diagnostics of anaerobic cocci
Identification of the pathogen requires a specific approach due to the microorganisms' sensitivity to oxygen.
- Main method: classical bacteriological examination. It includes inoculation of clinical material onto special complex media followed by cultivation under strict anaerobic conditions. This method allows not only the isolation of a pure culture but also the determination of its drug susceptibility.
- Rapid methods: used for the rapid confirmation of diagnosis, as cultivation of anaerobes takes a long time. In clinical practice, polymerase chain reaction (PCR) to detect bacterial DNA, laser-induced fluorescence, and gas-liquid chromatography—which allows the identification of specific bacterial metabolic products in the studied material—are actively used.
Principles of antibacterial therapy
Treatment of purulent-inflammatory diseases caused by members of the genus Veillonella must be based on the use of drugs with proven anti-anaerobic activity. Since infections are usually mixed in character, therapy is often comprehensive.
The basis of antibiotic therapy is formed by $\beta$-lactam antibiotics, among which drugs from the penicillin and cephalosporin groups are in highest demand. Metronidazole also possesses high clinical efficacy and is the drug of choice for many anaerobic processes. Clindamycin is widely used as a reliable alternative, penetrating well into inflammatory foci.
Briefly: answers to topical questions
What biochemical properties and metabolic features are characteristic of veillonellas?
Veillonellas are fastidious in their cultivation requirements and need complex nutrient media. A characteristic feature of their metabolism is the release of carbon dioxide ($CO_2$) during their life activity. In addition, certain species of these bacteria have the ability to produce porphyrins. Biochemical activity is manifested during growth under strict anaerobic conditions.
With which specific bacterial species do veillonellas most frequently form polymicrobial associations?
Veillonellas cause purulent-inflammatory processes predominantly as part of polymicrobial associations; they rarely occur as a monoinfection. In sources regarding abscesses and phlegmons of the soft tissues of the face and neck, veillonellas are listed among frequent pathogens alongside enterobacteria, streptococci, staphylococci, and Eikenella spp. It is also noted that microbial associations in these infections frequently include Fusobacterium nucleatum and actinomycetes.
To memorize their morphology, use the association: "Veillonellas are shadow twins of Neisseria." They look the same (gram-negative diplococci), but live in the "shadow" (without oxygen) and do not wear "clothing" (without a capsule).
Class and exam questions
What is the main visual similarity of veillonellas under the microscope?
In a smear, they appear as gram-negative diplococci, arranged in pairs, which is why they are often morphologically compared to Neisseria.
Can Veillonella be the sole cause of severe inflammation?
As a monoinfection, they are extremely rare. Their typical role in pathology is participation in mixed polymicrobial infections alongside other pathogens.
What media are required for the bacteriological inoculation of veillonellas?
For their cultivation, complex nutrient media and the creation of strict anaerobic conditions (complete absence of oxygen) are necessary.
What is characteristic of the metabolism of certain species of veillonellas?
During their life activity, they actively release carbon dioxide, and certain species are also capable of producing porphyrins.
What else to study on this topic
- Mechanisms of formation of polymicrobial associations in purulent-inflammatory processes.
- The working principle of gas-liquid chromatography in the diagnosis of anaerobic infections.
- Features of collection and transport of clinical material for strict anaerobes.
- Pharmacodynamics of metronidazole and clindamycin against anaerobic flora.
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