Evaluation of the in vitro activity of ceftaroline and its potential against a collection of hospital-acquired methicillin-resistant S.aureus and hospital-acquired methicillin-susceptible S.aureus isolates recovered from various clinical samples

Aim of the study was the evaluation of the in vitro activity of ceftaroline and its potential against a collection of Hospital-Acquired Methicillin-Resistant Staphylococcus aureus (HA-MRSA) and Hospital-Acquired Methicillin-Susceptible S. aureus (HA-MSSA) isolates. S. aureus isolates from outpatients were also examined. A total of 30 MSSA and 50 MRSA strains were studied.The isolates were collected during a four-year period (2006-2010) from the Pavia area (North-West of Italy). MICs and MBCs were performed in duplicate by broth dilution method (EUCAST 2012). Susceptibility category assessments for ceftaroline was made using EUCAST 2013 breakpoints. MICs of the antibiotics included in MicroScan Pos Breakpoint Combo Type 32 Panels (Siemens) were also evaluated. Genotyping was performed by PFGE. Ceftaroline MIC values for MSSA strains ranged from 0.06 mg/L to 0.5 mg/L and from 0.125 mg/L to 2 mg/L for MRSA strains, of which 4/50 exhibited a MIC value of 2 mg/L. The MIC value of these 4 isolates was confirmed by macromethod. Two out of four, clonally related, belonged to hVISA category. Furthermore, MIC50 and MIC90 were evaluated: MSSA MIC50 value was 0.125 mg/L, while MIC90 was 0.25 mg/L; MIC50 and MIC90 values of the MRSA were 0.5 mg/L and 1 mg/L, respectively. Finally, the bactericidal activity of this molecule was investigated by MBC method. Ceftaroline MIC and MBC values coincided in 96.25% of cases, only in 3 cases the MBC value was one dilution higher than MIC value. Ceftaroline demonstrated bactericidal activity against a large number of S. aureus, included MRSA and hVISA.