Comparative in vitro activity of four beta-lactam antibiotics in surgical wound fluid against staphylococci

Minimal inhibitory and bactericidal concentrations (MIC and MBC) of methicillin, dicloxacillin, cephalothin and cefuroxime were determined against 26 strains of staphylococci, using a broth dilution method with surgical wound fluid (WF) and Mueller-Hinton broth (MH) as test media. The staphylococci were all clinical isolates; 17 strains were coagulase-positive and 9 were coagulase-negative. The MIC-values of dicloxacillin and cephalothin estimated in MH were lower than those estimated in WF. For methicillin and cefuroxime the MIC-values in the two media were similar. With regard to MIC-values, the two penicillins were identical in WF, as were the two cephalosporins, but the cephalosporins were found to be more active than the penicillins, with an average of one dilution step. As regards the MBC to MIC ratios, no differences were found neither between the two media nor between the four antibiotics.