Staphylococcus aureus from hospital-acquired pneumonia from an Italian nationwide survey: Activity of ceftobiprole and other anti-staphylococcal agents, and molecular epidemiology of methicillin-resistant isolates

Objectives: To determine the prevalence of Staphylococcus aureus from hospital-acquired pneumonia (HAP) in Italy and the susceptibility to ceftobiprole and comparators of MSSA and MRSA isolates. A secondary objective was to characterize the clonality and acquired resistance and virulence genes of MRSA. Methods: Consecutive non-replicate isolates from HAP were collected from 13 laboratories distributed across Italy, from January to May 2016. Antimicrobial susceptibility testing was performed by broth microdilution, and results were interpreted according to the EUCAST breakpoints. All MRSA isolates were subjected to WGS using an Illumina platform. Clonality and resistance and virulence gene content were investigated with bioinformatics tools. Results: Among 333 isolates from HAP, S. aureus was the third most common pathogen (18.6%). The proportion of MRSA was 40.3%. Susceptibility to ceftobiprole was 100% for MSSA and 95.5% for MRSA. Lower susceptibility rates of 78.4% and 94.6% in MSSA and 36.4% and 12.1% in MRSA isolates were observed for erythromycin and levofloxacin, respectively. The MRSA from HAP mostly belonged to clonal complex (CC) 22 (47.0%), CC5 (25.8%) and CC8 (15.2%), with a minority of other lineages (ST1, ST6, ST7, ST30, ST152 and ST398). Acquired resistance and virulence genes in most cases exhibited a clonal distribution. The three ceftobiprole-resistant isolates exhibited an MIC of 4 mg/L and belonged to ST228-MRSA-I of CC5. Conclusions: S. aureus is an important cause of HAP in Italy. Ceftobiprole exhibited good in vitro activity against S. aureus isolated from HAP, including MRSA. A trend to replacement of ST228 with ST22 was noticed compared with previous studies.