Comparison of agar dilution, microdilution, and disk elution methods for measuring the synergy of cefotaxime and its metabolite against anaerobes.
The activities of cefotaxime (CTX) and desacetyl cefotaxime (des-CTX) were tested both singly and in combination against 173 anaerobic clinical isolates. The MIC of CTX for 50% of 60 Bacteroides fragilis isolates was 22.4 micrograms/ml in broth, compared with 47.4 micrograms/ml in agar. This reduced efficacy in agar was seen with all species tested and is in apparent conflict with reported clinical efficacy of the drug. Synergy between CTX and des-CTX was observed with 70 to 100% of the isolates, including 60% of all Bacteroides spp. tested. The susceptibility results in a synergy system correlated well with those noted in a broth-disk elution method incorporating 32 micrograms of CTX and 8 micrograms of des-CTX per ml. The correlation was poorer when the broth-disk method contained 16 micrograms of CTX and 8 micrograms of des-CTX per ml.
Smith
J A
JA
Henry
D
D
Ngui-Yen
J
J
Castell
A
A
Coderre
S
S
D001421:Bacteria, Anaerobic / Q000187:drug effects*; D001439:Bacteroides / Q000187:drug effects*; D001441:Bacteroides fragilis / Q000187:drug effects; D002439:Cefotaxime / Q000031:analogs & derivatives* / Q000494:pharmacology*; D003013:Clostridium / Q000187:drug effects*; D003016:Clostridium perfringens / Q000187:drug effects; D004352:Drug Resistance, Microbial; D004357:Drug Synergism; D008826:Microbial Sensitivity Tests
C029281:desacetylcefotaxime; D002439:Cefotaxime