Abstract:Objective To understand the in vitro susceptibility of cethromycin, a ketolide antibiotic, to clinically isolated methicillin-susceptible Staphylococcus aureus (MSSA) and relationship of different molecular types of MSSA with minimum inhibitory concentration(MIC) value of cethromycin. Methods 118 strains of MSSA isolated from different clinical specimens in Nanshan Hospital of Shenzhen from 2011 to 2015 were collected, MIC values of cethromycin and other 9 commonly used antistaphylococcal agents against MSSA were determined by broth dilution method and Kirby-Bauer method. Multilocus sequence typing (MLST) technique was used to classify them into different genotypes, relationship of MSSA type and MIC values of cethromycin to MSSA was observed. Results MSSA was sensitive to linezolid, vancomycin, furantoin, teicoplanin, and amoxicillin/clavulanic acid, 2 strains were intermediate to cethromycin, and 21 strains were resistant to cethromycin, resistance rate was 19.5%, resistance rate to erythromycin was as high as 60.2%. MSSA was divided into 32 ST types, and 20 strains were new ST types, the top three ST types were:15 ST7 (12.7%), 12 ST188 (10.2%) and 12 ST59 (10.2%). Conclusion Resistance of MSSA to macrolide antibiotics is severe, and cethromycin is more effective than erythromycin in treating MSSA. ST7, ST188, ST59 and ST398 are the main MLST of MSSA strains isolated from this hospital.