Antibiotic resistance and molecular epidemiology of methicillin-resistant Staphylococcus aureus from lower respiratory tract: multi-resistance and high prevalence of SCCmec III type.

We sought to study antibiotic resistance and molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) from lower respiratory tracts of patients in Shanghai Pulmonary Hospital. Hundred and seven strains of MRSA were isolated from the patients of nine wards. The tests for antibiotic resistance (Kirby-Bauer paper dispersion method), the Panton-Valentine Leukocidin (PVL) and Staphyloccoccal Cassette Chromosome mec (SCCmec) genes (PCR), and homology analysis (32 randomly selected MRSA strains; pulsed-field gel electrophoresis) were carried out. All 107 strains were susceptible to vancomycin, teicoplanin, and linezolid, but highly or completely resistant to tetracycline, gentamicin, clindamycin, levofloxacin, azithromycin, erythromycin, trimethoprim/sulphamethoxazole, and ciprofloxacin. All 107 strains were negative for PVL gene. Most of the strains (81.3%) were SCCmec III type, while the SCCmec II and IV types were less frequent (15.9 and 2.8%, respectively). No SCCmec I or V types were detected. The homology analysis test showed that 32 MRSA strains could be divided into 4 groups: type A (25 strains), type B (5 strains), type C (1 strain), and type D (1 strain). The type A included 3 subtypes: A1 (17 strains), A2 (1 strain), and A3 (7 strains). Further, most of the strains were isolated from the same wards or units (e.g., intensive care unit or tuberculosis wards) within a short period of time, indicating an outbreak status. In conclusion, the observed MRSA from low respiratory tracts from patients at Shanghai Pulmonary Hospital were multiple-resistant, with the SCCmec III being the main documented genotype.