In vitro activity of ceftobiprole on 440 Staphylococcus aureus strains isolated from bronchopulmonary infections

We assessed the in vitro activity of ceftobiprole on 440 Staphylococcus aureus clinical strains isolated from bronchopulmonary infections (2010-2014).

S. aureus isolates were characterized for methicillin resistance, PVL status, and clonal complex. All isolates were tested for minimal inhibitory concentrations (MIC) determination by broth microdilution method for ceftobiprole, ceftaroline fosamil, and comparator antibiotics (linezolid, tigecycline, vancomycin, and daptomycin).

A total of 325 (74%) strains were methicillin-susceptible S. aureus (MSSA) and 115 (26%) were methicillin-resistant S. aureus (MRSA); 105 (24%) S. aureus strains were PVL-positive, including 35.2% (37/105) MRSA and 64.8% (68/105) MSSA. Ceftobiprole was highly active against S. aureus with MIC₉₀ of 1 mg/L, MICs ranging between 0.12 and 4mg/L (only one resistant strain, MIC of 4 mg/L). MIC₅₀ and MIC₉₀ were twice lower in MSSA than MRSA. Moreover, PVL⁺ MRSA were slightly more susceptible to ceftobiprole (MIC₅₀ of 0.5 mg/L and MIC₉₀ of 1 mg/L) than PVL^- MRSA (MIC₅₀ and MIC₉₀ of 1 mg/L). The ceftobiprole-resistant strain was also resistant to ceftaroline fosamil and presented the D239L mutation in PBP2A. The comparator antibiotics were equally active on the strains tested, with MIC₉₀ of 0.5 mg/L for ceftaroline fosamil, tigecycline, and daptomycin; 1 mg/L for vancomycin; and 2 mg/L for linezolid.

Our results suggest that ceftobiprole is highly active against S. aureus and is an effective alternative to vancomycin or linezolid in the management of staphylococcal pneumonia. However, close monitoring of isolates should be maintained to prevent resistant strain diffusion.