Susceptibility at high inoculum of penicillin-resistant Staphylococcus aureus to six cephalosporins

Six cephalosporins (currently available for clinical use or undergoing clinical trials) were tested by tube dilution method against high inoculum (107 colony forming units) of 37 strains of penicillin resistant Staphylococcus aureus. 3.1 μg/ml of cephalothin inhibited 100% of strains while higher concentrations of cefoxitin, cephapirin, cefamandole, cephalexin and cephradine were required. The percent of strains with minimal inhibitory concentration higher than 3.1 μg/ml ranged between 10.8% (cefoxitin) and 100% (cephradine). These findings support the observation that cephalothin is less susceptible to inactivation than the other cephalosporins. Although the exact clinical implication of these findings has not been established, cephalothin might be the cephalosporin of choice for treatment of severe infections caused by penicillin resistant Staphylococcus aureus