The microbial spectrum of brain abscess with special reference to anaerobic bacteria.

The bacteriological and clinical findings of 18 cases of brain abscess are presented. Identification and antimicrobial susceptibility of anaerobic strains was performed both by conventional methods and the newer RapID ANA II panel and E-test methods, respectively. Characterization of the anaerobic isolates was done by restriction fragment length polymorphism (RFLP). Anaerobic or aerobic organisms alone were recovered in three (16.6%), and mixed aerobic and anaerobic in another three (16.6%) patients. There were nine anaerobic isolates. The predominant anaerobes were Prevotella melaninogenicus (four isolates), Bacteroides preacutus (three isolates), Fusobacterium nucleatum and Peptostreptococcus sp. (one isolate each). A total of six aerobic isolates, all of which were Gram-positive cocci were recovered. All the anaerobic isolates were susceptible to metronidazole, but two isolates of P. melaninogenicus were resistant to penicillin. There was complete agreement between the identification based on biochemical profiles and RFLP patterns. These findings indicate the microbial complexity of brain abscess and the need to target antimicrobial therapy against both the aerobic and anaerobic components of infection.