Evaluation of in vitro methods for testing ceftriaxone against anaerobic bacteria, including quality control guidelines.

Tests with 100 anaerobic bacterial isolates demonstrated comparability between ceftriaxone MICs obtained with the reference agar dilution procedure and those obtained with a broth microdilution susceptibility testing procedure. The aerobically incubated thioglycolate disk elution test was also evaluated. Six 30-micrograms ceftriaxone disks in 5 ml of thioglycolate separated strains for which MICs were less than or equal to 32 micrograms/ml from those for which MICs were greater than or equal to 64 micrograms/ml (6% overall discrepancies). Quality control limits for ceftriaxone agar dilution tests were determined to be as follows: Bacteroides fragilis ATCC 25285, 32 to 128 micrograms/ml; and Bacteroides thetaiotaomicron ATCC 29741, 64 to 256 micrograms/ml.