Abstract:

Objective To discuss the genotype distribution of methicillin-resistant Staphylococcus aureus （MRSA） in a tertiary hospital and to discuss the correlation among different molecular types of the strains， and to construct the resistance profile model under different genetic backgrounds. Methods A total of 204 strains of Staphylococcus aureus （S. aureus）from 25 departments of the hospital were selected. The automatic VITEK 2 Compact system and E-test strips were used to detect the antimicrobial susceptibility of the strains. The detection of mecA gene by the polymerase chain reaction （PCR） method was used as the confirmatory experiment， the abilities of cefoxitin （FOX） and（or） oxacillin （OXA） were compared as phenotypic detection methods to screen MRSA. The molecular typing of MRSA strains was carried out by PCR method， including Staphylococcal proteinA gene （spa） determination， accessory gene regulator （agr） typing， multilocus sequence typing （MLST）， and staphylococcal chromosomal cassettes mec （SCCmec） typing. The resistance profile was constructed combing with antimicrobial susceptibility tests results and molecular typing results. Results A total of 39 MRSA strains were obtained by detecting the mecA gene. A total of 51 phenotypic MRSA strains were identified by testing FOX and OXA. In spa typing， 57 different types were identified， including 5 new types （t20226， t20227， t20228， t20229， and t20230）， with the main types being t309 （30.9%）， t078 （11.8%）， and t437 （11.8%）. In agr typing， 94.9% of MRSA belonged to agr Ⅰ. The MLST analysis results of MRSA populations showed that ST59 clone （61.5%） was the most prevalent， followed by ST72 （20.5%）. A total of 87.2% of MRSA carried type Ⅳ SCCmec， with subtypes Ⅳa accounting for 24 strains and subtype ⅣF accounting for 10 strains. Conclusion The main genotype of MRSA is ST59-t437-agr Ⅰ-Ⅳa and its resistance profile is primarily characterized by resistance to FOX-OXA-penicillin （PEN）-erythromycin （ERY）-clindamycin （CLI）.

Key words: Staphylococcus aureus, Methicillin-resistant Staphylococcus aureus, Cefoxitin, Oxacillin, Resistance profile