Differences between cephalothin and newer parenterally absorbed cephalosporins in vitro: a justification for separate disks.

The activities of cefamandole and cefoxitin in vitro were compared with that of cephalothin against staphylococci and gram-negative bacilli. Cephalothin was the most active agent against staphylococci. Cefamandole exhibited the greatest activity against the Enterobacteriaceae, with the exceptions of Serratia marcescens and indole-positive Proteeae, against which cefoxitin was the most active antibiotic. The activity of newer cephalosporins that are resistant to the beta-lactamases of gram-negative bacteria renders untenable the status of cephalothin as the class representative of the cephalosporins for susceptibility testing.