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Chapter: Microbiology and Immunology: Bacteriology: Nonsporing Anaerobes

Nonsporing Anaerobes

Most of the important anaerobic Gram-positive cocci belong to the genus Peptostreptococcus. The cocci are small and measure 0.2–2.5 mm in size.

Anaerobic Cocci

Anaerobic Gram-Positive Cocci

Most of the important anaerobic Gram-positive cocci belong to the genus Peptostreptococcus. The cocci are small and measure 0.2–2.5 mm in size. Many of the cocci are aerotolerant and grow well in air supplemented with 10% CO2. These Gram-positive cocci are normal inhabitants of the oral cavity, gastrointestinal tract, genitourinary tract, and skin. These bacteria on spreading from these sites to other normally sterile sites may cause several clinical infections:

a)        Bacteria colonizing the skin can cause cellulitis and infec-tions of the soft tissue;

b)         Bacteria in the intestine can cause intra-abdominal infection;

c)        Bacteria in the genital tract can cause pelvis abscess, salpingitis, and endometritis; and

d)       Bacteria invading blood stream can cause infections in bones and visceral organs.

Peptostreptococcus anaerobius is most commonly associated withpuerperal sepsis and Peptostreptococcus magnus with abscess. The laboratory diagnosis of the infection caused by these cocci depends on the isolation of the bacteria by culture. Clinical specimens are inoculated on blood agar or other enriched agar and incubated for at least 5–7 days in anaerobic conditions, unlike other anaerobic bacteria that typically grow in 1–2 days. While collecting the specimens, care should be taken to prevent contamination of the specimens withPeptostreptococcus that normally colonize the mucosal membrane and skin surface.

The cocci are often found in large numbers in pus from suppurative lesions; hence Gram staining of pus smears is frequently helpful in diagnosis.

The cocci are generally sensitive to imipenem, chlorampheni-col, and metronidazole. They are intermediately sensitive to broad-spectrum cephalosporins, tetracyclines, and clindamycin. They are resistant to streptomycin and gentamicin. Most infections are mixed, the cocci being present along with anaerobic Gram-negative bacilli and clostridia. Hence, broad-spectrum antibiotics effective against all these pathogens are usually given for treatment.

Anaerobic Gram-Negative Cocci

The genus Veillonella spp. includes anaerobic Gram-negative cocci of varying size occurring in pairs, short chains, or clus-ters. These cocci normally colonize the mouth, intestines, and genitourinary tract. Veillonella parvula is the species frequently reported from clinical specimens, but its role in causation of the disease is not known.

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