Antimicrobial susceptibility testing of anaerobic bacteria

Antimicrobial susceptibility testing of anaerobic bacteria has assumed greater importance in recent years because of (1) an increase in recognition of the clinical significance of anaerobes, (2) a decrease in predictability of susceptibility patterns, (3) the appearance of new antimicrobial agents with variable activity against anaerobes, (4) an increase in use of and demand for susceptibility data by clinicians, and (5) the availability of a standardized reference and practical methods for susceptibility testing of anaerobes. The broth microdilution and broth disk-elution techniques are suitable for clinical microbiology laboratories and have been shown to provide results comparable to those obtained with the reference agar-dilution method developed by the National Committee for Clinical Laboratory Standards. The ability to produce beta-lactamase has been demonstrated in most strains of the Bacteroides fragilis group and in over half of other Bacteroides. Increasing resistance of B. fragilis to clindamycin has been reported, and the newer beta-lactam antibiotics, including moxalactam, piperacillin, cefoperazone, and cefotaxime, have variable activity against this organism. Most medical centers should perform susceptibility tests on anaerobes isolated from patients with bacteremia and bone and joint and central nervous system infections and on those anaerobes isolated in pure culture from other specimens and also should test anaerobic isolates on special request of clinicians.