Bacteroides and Fusobacterium
Several anaerobic culture systems are available. Normal blood agar plates can be used. Species are identified by gram stain, resistance to bile, antimicrobial susceptibility, and a battery of biochemical tests.
The selection of antimicrobials depends on whether the infection is above or below the diaphragm. Infections of the head, neck, lung, pleura, and the brain are usually associated with anaerobes of the oral flora. The bacteria involved i.e. fusobacterium, peptostreptococci, and B. melaninogenicus are ordinarily susceptible to penicillin and for many years, this was considered to be the drug of choice, with clindamycin and chloramphenicol being 2nd line drugs. In recent years, there had been a steady rise in the incidence of resistance and some of the newer cephalosporins are being used as front-line.
For infections below the diaphragm e.g. abdominal, pelvic, and soft tissue infections, the predominant pathogen is B. fragilis. Not only is this species the most virulent of the anaerobes, many strains have become resistant to tetracycline, penicillins, and many cephalosporins. The emergence of clindamycin resistance has also been documented and there had been scattered reports of resistance to metronidazole and chloramphenicol. In infections below the waist, a successful regimen must also cover the common accompanying aerobic and facultatively aerobic species.