Genotyping of methicillin-resistant Staphylococcus aureus isolates causing invasive infections using spa typing and their correlation with antimicrobial susceptibility

Correlation of antimicrobial susceptibility patterns with particular spa types could help physicians select appropriate antibiotics for the treatment of invasive methicillin-resistant Staphylococcus aureus (MRSA) infections. The aim of this study was to investigate invasive MRSA isolates through delineating the molecular typing results and correlating them with antibiotic susceptibility testing results. A total of 670 non-duplicate mecA-positive MRSA isolates from patients with invasive infections were collected from a 5-year nationwide antimicrobial surveillance programme [Tigecycline In vitro Surveillance in Taiwan (TIST)] and 58 spa types were identified among 639 isolates (95.4%) by determining the allelic profile of the spa gene using PCR and nucleotide sequencing. Six major spa types, including spa t002 (n = 103; 15.4%) and t037 (n = 253, 37.8%), were classified as healthcare-associated MRSA (HA-MRSA; 53.1%), while t437 (n = 151; 22.5%), t441 (n = 13; 1.9%), t1081 (n = 19; 2.8%) and t3525 (n = 14; 2.1%) were classified as community-associated MRSA (CA-MRSA; 29.4%). Antimicrobial susceptibility was determined by agar dilution or broth microdilution for various antibiotics, and Etest was also used both for daptomycin and vancomycin. The declining trend in vancomycin minimum inhibitory concentration (MIC) was in parallel with an increasing frequency of CA-MRSA. Antibiotic susceptibility patterns were correlated with particular spa types and this correlation could help physicians select appropriate antibiotics for the treatment of invasive MRSA infections.