Evaluation of the in vitro activity of ceftobiprole against clinical isolates of Staphylococcus aureus

Background and aims: Ceftobiprole is a new cephalosporin characterized by a potent activity against Gram-positive and Gram-negative bacterial pathogens. It is noting that ceftobiprole has a strong affinity for penicillin binding proteins including PBP 2A, which mediates resistance to beta-lactams in methicillin (oxacillin)-resistant coagulase- negative staphylococci and Staphylococcus aureus (MRSA). The aim of the current study was to examine the antimicrobial activity of ceftobiprole against clinical isolates of S. aureus recently collected at our institution.
Materials and methods: One hundred and forty blood isolates of S. aureus were evaluated, including methicillin-susceptible (MSSA, n=70) and MRSA (n=70) strains. Twenty additional MRSA isolates obtained from different sites (including skin and soft tissues, blood, and lower respiratory tract) and characterized by borderline susceptibility to vancomycin were also studied to assess the ability of ceftobiprole to overcome this worrisome trait. MIC values of ceftobiprole were determined by Etest strips and results were interpreted according to EUCAST guidelines.
Results and conclusions: Study isolates were consistently susceptible to ceftobiprole, with MIC values ranging from 0.125 mg/L to 2 mg/L. Overall, MIC50 and MIC90 were 0.25 mg/L and 0.5 mg/L, respectively. Ceftobiprole showed in vitro activity against all S. aureus isolates, with small differences among groups selected on the basis of resistance to methicillin and/or reduced susceptibility to vancomycin. Thus, ceftobiprole appears a valid choice for treating infections caused by S. aureus, even when susceptibility results are not yet available. Additionally, ceftobiprole may be a valid option in the case of reduced susceptibility to vancomycin.