In vitro antibacterial activity of ceftobiprole against clinical isolates from French teaching hospitals: proposition of zone diameter breakpoints

International audienceThe aims of this study were to determine the in vitro activity profile of ceftobiprole, a pyrrolidinone cephalosporin, against a large number of bacterial pathogens and to propose zone diameter breakpoints for clinical categorisation according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) minimum inhibitory concentration (MIC) breakpoints. MICs of ceftobiprole were determined by broth microdilution against 1548 clinical isolates collected in eight French hospitals. Disk diffusion testing was performed using 30μg disks according to the method of the Comité de l'Antibiogramme de la Société Française de Microbiologie (CA-SFM). The in vitro activity of ceftobiprole, expressed by MIC (MICs for 50% and 90% of the organisms, respectively) (mg/L), was as follows: meticillin-susceptible , 0.25/0.5; meticillin-resistant (MRSA), 1/2; meticillin-susceptible coagulase-negative staphylococci (CoNS), 0.12/0.5; meticillin-resistant CoNS, 1/2; penicillin-susceptible , ≤0.008/0.03; penicillin-resistant , 0.12/0.5; viridans group streptococci, 0.03/0.12; β-haemolytic streptococci, ≤0.008/0.016; , 0.25/1; , 64/128; Enterobacteriaceae, 0.06/32; , 4/16; , 0.5/64; , 0.03/0.12; and , 0.25/0.5. According to the regression curve, zone diameter breakpoints could be 28, 26, 24 and 22mm for MICs of 0.5, 1, 2 and 4mg/L respectively. In conclusion, this study confirms the potent in vitro activity of ceftobiprole against many Gram-positive bacteria, including MRSA but not , whilst maintaining a Gram-negative spectrum similar to the advanced-generation cephalosporins such as cefepime. Thus ceftobiprole appears to be well suited for the empirical treatment of a variety of healthcare-associated infections