Characterization and Clonal Diffusion of Ceftaroline Non-Susceptible MRSA in Two Hospitals in Central Italy

Background: Ceftaroline represents a novel fifth-generation cephalosporin to treat infections caused by methicillin-resistant Staphylococcus aureus (MRSA). Methods: Ceftaroline susceptibility of 239 MRSA isolates was assessed by disk diffusion and a MIC test strip following both EUCAST and CLSI guidelines. Non-susceptible isolates were epidemiologically characterized by pulsed-field gel electrophoresis, spa typing, and multilocus sequence typing, and further investigated by PCR and whole genome sequencing to detect penicillin-binding protein (PBP) mutations as well as antibiotic resistance and virulence genes. Results: Fourteen isolates out of two hundred and thirty-nine (5.8%) were non-susceptible to ceftaroline (MIC > 1 mg/L), with differences between the EUCAST and CLSI interpretations. The characterized isolates belonged to seven different pulsotypes and three different clones (ST228/CC5-t041-SCCmecI, ST22/CC22-t18014-SCCmecIV, and ST22/CC22-t022-SCCmecIV), confirming a clonal diffusion of ceftaroline non-susceptible strains. Mutations in PBPs involved PBP2a for ST228-t041-SCCmecI strains and all the other PBPs for ST22-t18014-SCCmecIV and ST22-t022-SCCmecIV clones. All isolates harbored antibiotic resistance and virulence genes with a clonal distribution. Conclusion: Our study demonstrated that ceftaroline non-susceptibile isolates belonged not only to ST228 strains (the most widespread clone in Italy) but also to ST22, confirming the increasing role of these clones in hospital infections.