Biological Properties and Taxonomy
Among all anaerobic gram-negative cocci, the genus Veillonella is the most relevant to clinical medicine. The clinically significant species most frequently encountered in human pathology include V. atypica, V. dispar, and V. parvula.
Morphologically, they are gram-negative coccoid bacteria. In microscopic smears, cells typically appear in pairs (as diplococci), short chains, or less frequently, singly. In appearance and spatial arrangement, these microorganisms strongly resemble Neisseria species, a factor to keep in mind during initial microscopy. Key morphological features of veillonellae are their absolute non-motility and lack of a capsule.
Regarding cultural and biochemical properties, these bacteria are highly fastidious. They grow exclusively on complex nutrient media under strict anaerobic conditions. Their metabolic hallmark is the active production of carbon dioxide ($CO_2$) during growth, with certain specific species capable of producing porphyrins.
Ecology and Pathogenesis of Infection
Veillonellae are natural inhabitants of the human body and part of the normal microbiota. Their most typical niches are the mucous membranes of the oral cavity and nasopharynx. Additionally, they are thought to inhabit the gut microbiome.
Although they are normal flora, a decrease in host resistance enables them to cause various suppurative infections. The main pathogenic feature of infections caused by anaerobic cocci lies in the nature of the inflammation itself. These microorganisms rarely act as the sole causative agent (monoinfection is atypical for them). Instead, they predominantly constitute polymicrobial associations, proliferating alongside other aerobic and anaerobic bacteria. Thus, they act as classic participants in mixed infections, exacerbating their clinical course.
Laboratory Diagnosis of Anaerobic Cocci
Detecting these pathogens requires a specific approach due to their oxygen sensitivity.
- Primary method: Classical bacteriological culture. This involves inoculating clinical specimens onto specialized complex media followed by incubation under strict anaerobic conditions. This method isolates pure cultures and determines antimicrobial susceptibility.
- Rapid methods: Used for swift diagnostic confirmation because anaerobe cultivation is time-consuming. Clinical practice utilizes polymerase chain reaction (PCR) to detect bacterial DNA, laser-fluorescence methods, and gas-liquid chromatography (GLC) to identify specific bacterial metabolic products in clinical samples.
Principles of Antimicrobial Therapy
The management of suppurative infections caused by Veillonella species relies on agents with proven anti-anaerobic activity. Because these infections are typically mixed, therapy is often combination-based.
Beta-lactam antibiotics form the foundation of antimicrobial therapy, with penicillins and cephalosporins being the most frequently utilized. Metronidazole also shows high clinical efficacy and serves as the drug of choice for many anaerobic processes. Clindamycin is widely used as a reliable alternative due to its excellent penetration into inflammatory foci.