Gram-negative anaerobic bacilli and cocci

Bacteria from the group Gram-negative anaerobic bacilli and cocci are difficult to cultivate, so it is problematic to identify them as the causative agent of the disease. We include clinically important genus Bacteroides, Prevotella, Fusobacterium, Mobiluncus and Veillonella.

= Gram negative anaerobic bacilli = Anaerobic G− bacilli are part of the natural bacterial flora, often acting as opportunistic pathogens. These pleomorphic bacteria are difficult to cultivate. The main pathogenic mechanism is non-specific tissue damage caused by acid production. Bacteroides and fusobacteria produce enzymes, which facilitate their penetration into tissues.

These bacteria can cause infections anywhere in the human body: oral, pleuropulmonary, intra-abdominal, periodontal infections, infections in the small pelvis, and female genital infections. They are also infectious agents in tissues damaged by injury or surgery. Abscesses filled with foul-smelling pus are formed at the site of affliction. Lincomycin, chloramphenicol, clindamycin and metronidazole are used for therapy. Surgery (incision, drainage) is often necessary.

Bacteroides spp.
The genus Bacteroides is part of the natural bacterial flora, some species are potentially pathogenic. Their membrane contains sphingolipids and there is diaminopimelic acid in their wall.

Bacteroides are gram-negative pleomorphic rods with round ends, usually encapsulated. They are characterized by resistance to bile acids. They massively colonize the large and small intestine, where they play a role in the digestion of complex molecules, and the upper respiratory tract. The microflora of the vagina contains B. fragilis, B. capillosus or B. ureolyticus. Their endotoxin has a low biological activity.

Pathogenicity
Among the most important pathogens is B. fragilis with a polysaccharide capsule as a virulence factor. It can cause peritonitis, surgical site infection, gastrointestinal infections and appendicitis. It also inhibits phagocytosis and, like other species of this genus, it is resistant to beta-lactams, aminoglycosides, and erythromycin. Tetracycline-resistant species have recently emerged. The genus Bacteroides also includes e.g. B. ovatus, B. vulgatus and B. gracilis.

Prevotella spp.
Bacteria of the Prevotella genus are gram-negative anaerobic fermenting rods related to the Bacteroides genus. Individual species include P. oris, P. buccae, P. dentalis, and P. melaninogenica. Diseases caused by these bacteria include infections of the wound, urinary tract, and respiratory tract (angina, sinusitis); they can also be infectious agents in the formation of abscesses in the oral cavity, for example after a human bite. The production of beta-lactamase makes them resistant to beta-lactam antibiotics.

Fusobacterium spp.
The genus Fusobacterium includes gram-negative anaerobic rods, which are part of the natural bacterial flora of the upper respiratory, digestive and genital tracts. Pathogenic species include F. necrophorum and F. nucleatum. Fusobacterium causes surgical and traumatic wound infections and complicates animal bites. It can be identified in mixed cultured causing pneumonia, thoracic empyema, intra-abdominal infection and abscesses. Rarely, fusobacterium can cause osteomyelitis.

F. nucleatum is part of dental plaque, invasiveness is enabled by the ability to adhere to both G-negative and G-positive biofilm. Bacteria can also cause inflammation of the periodontium. F. necrophorum causes serious infections of children and adolescents, a severe condition is necrotizing tonsillitis accompanied by the formation of pablans and abscesses.

Mobiluncus spp.
Bacteria of the Mobiluncus genus are gram labile anaerobic moving rods. They are isolated from the mucosa of the female reproductive system with bacterial vaginosis, often together with Gardenerella vaginalis and other bacteria. They are also found in women without clinical symptoms. This genus contains M. curtisii and M. mulieris

= Gram-negative anaerobic cocci = The genus G− anaerobic cocci includes Acidaminococcus spp., Megasphaera spp., which are part of the natural bacterial flora. Bacteria of the genus Veillonella are the most important clinically.

Veillonella spp.
Bacteria of the Veillonella genus are gram-negative anaerobic cocci, which usually form clusters or pairs. Under UV light, they are red fluorescent. They are part of the natural bacterial flora of the oral cavity, nasopharynx, digestive tract and female genitalia. They can cause mixed infections, exceptionally they have been identified as agents of meningitis, osteomyelitis and periodontal infections. The genus includes V. parvula, V. montpellierensis or V. alcalescens. V. parvula may be the cause of endocarditis.