Determination of an inoculum effect with various cephalosporins among clinical isolates of methicillin-susceptible Staphylococcus aureus.

Publication Date



Antimicrob Agents Chemother. 2010 May; 54(5): 2206–2208.


Using 98 clinical methicillin-susceptible Staphylococcus aureus isolates of known beta-lactamase (Bla) type, we found a pronounced inoculum effect for cephalexin (mostly Bla type A and C strains), a mild inoculum effect for cephalothin (especially types B and C), and no inoculum effects for ceftriaxone and cefuroxime. Ceftobiprole showed the lowest MICs at a high inoculum but with a slight increase for Bla-positive versus Bla-negative strains. Since a potential therapeutic effect associated with a cephalosporin inoculum effect has been described, further studies are warranted.


Anti-Bacterial Agents, Ceftriaxone, Cefuroxime, Cephalexin, Cephalosporins, Cephalothin, Humans, Methicillin, Microbial Sensitivity Tests, Staphylococcal Infections, Staphylococcus aureus