Objectives: We carried out a nationwide study aimed at the determination of the molecular epidemiology and antibiotic resistance mechanisms of invasive Staphylococcus aureus in 21 Spanish hospitals.
Methods: The distributions of molecular markers, including antibiotic resistance genes, were investigated in 203 S. aureus, comprising 90 methicillin-resistant S. aureus (MRSA) and 113 methicillin-susceptible S. aureus (MSSA). Antimicrobial susceptibility was determined by standard methods. Panton-Valentine leucocidin (PVL) detection, staphylococcal cassette chromosome mec (SCCmec) types and agr types were performed/determined by PCR. All isolates were genotyped by PFGE after digestion of chromosomal DNA with SmaI. Multilocus sequence typing and spa-typing were also performed.
Results: In MRSA isolates, 74.4% were agr allotype II and were positive for SCCmec IV. Sixty-nine spa-types were identified, 18 in MRSA and 57 in MSSA. Both MRSA and MSSA variants were detected in six spa-types (8.7%). The majority of S. aureus (51.2%) were grouped into four spa-types (t067, t002, t012 and t008). The spa-type t067 was detected in 18 of the 21 (85.7%) participating hospitals, including both MRSA and MSSA in six of them; in total, 25.9% of our isolates were spa-type t067 (49% in MRSA) in comparison with 0.6% in a central spa-typing database. The prevalence of the ant(4')-Ia and msrA/msrB genes was significantly higher in the MRSA spa-type t067 than in the other MRSA spa-types. Association between spa-type t067 and ST125 is described here for the first time. A high prevalence (36.4%) of PVL-positive MSSA was detected.
Conclusions: A higher than expected prevalence of spa-type t067 isolates was found among invasive MRSA in Spain. The oxacillin, tobramycin, erythromycin and ciprofloxacin resistance profile of spa-type t067 isolates was linked to the presence of ant(4')-Ia and msrA or msrB genes.