Prevalence of Fosfomycin Resistance in Methicillin-Resistant <i>Staphylococcus aureus</i> Isolated from Patients in a University Hospital in China from 2013 to 2015

In this study, we investigated the fosfomycin susceptibility rates among different methicillin-resistant Staphylococcus aureus (MRSA) clones. A total of 293 MRSA isolates obtained from Sir Run Run Shaw hospital during 2013-2015 were tested for fosfomycin susceptibility. The overall fosfomycin resistance rate among these MRSA isolates was 53.2%. Although 91.9% of the ST5 MRSA isolates (MIC50>1,024 mg/L) were resistant to fosfomycin, no fosfomycin-resistant isolate was found among the 69 ST59 MRSA isolates (MIC50/90, 0.5/4 mg/L). The fosfomycin resistance rate among the MRSA isolates recovered from skin and soft tissue infections was 19.1%, which was lower than the rates detected among MRSA isolates from other types of invasive infections. The fosfomycin resistance rate in community-onset MRSA was 30.2%, which was lower than that detected in healthcare-associated MRSA of 70.7%. One MRSA isolate had the fosB7 gene, whereas most (127/156) of the fosfomycin-resistant MRSA isolates had deletions in glpT genes. These findings highlight the importance of monitoring the fosfomycin susceptibility in MRSA isolates for epidemiological purposes.