The discovery of multidrug resistant Staphylococcus aureus harboring novel SaRImsr isolated from retail foods

作者：Zhang, Feng; Wu, Shi; Huang, Jiahui; Dai, Jingsha; Zhang, Jumei; Yang, Runshi; Xue, Liang; Zhao, Miao; Wang, Juan; Ding, Yu; Chen, Moutong^*; Wu, Qingping^*

来源：Food Control, 2022, 135: 108739.

DOI：10.1016/j.foodcont.2021.108739

• SaRI(msr)
• mef(D)-msr(F)
• Antibiotic resistance islands
• Macrolides
• Multidrug resistance

Food-borne Staphylococcus aureus has shown multidrug resistance. According to our previous studies, most S. aureus isolated from retail foods in China exhibited resistance to a variety of antimicrobials. Further Genome Wide Association Study (GWAS) revealed that a novel gene cluster, containing erythromycin-resistant genes, mef (D)-msr(F), existed in 19 isolates. In this study, we aim to investigate the distribution and transmission of this novel gene cluster in these isolates and to further characterize it. As a result, the msr(F)-positive S. aureus isolates mainly belong to ST7 (n = 14), sporadically to ST14 (n = 4), and ST88 (n = 1) most of which showed multidrug resistance (MDR) phenotype. Different virulence factors (VFs) and antimicrobial resistance genes (ARGs) were identified by genomic mining in msr(F)-positive strains. In addition, core genome phylogenetic analysis revealed that most of the msr(F)-positive strains (14/19) were closely related despite different isolation time. Two types of antibiotic resistance islands, SaRI(msr)-I (15.1 kb) and SaRI(msr)-II (16-17 kb) carrying mef(D)-msr(F), were identified in their chromosomes. Importantly, the novel SaRI(msr)-I was inserted into rpsI gene which encoded 30S ribosomal protein S9 on the chromosome. SaRI(msr)-II was also inserted into rpsI but four ORF frames downstream of rpsI were absent. Within the SaRI(msr)-I and -II, an operon structure consisting of ARGs, mef(D) and msr(F), and a site-specific integrase gene int were identified. Finally, the excision and cyclization of the SaRI(msr) and operon mef(D)-msr(F) were verified by two-step PCR. This study is the first report of MDR S. aureus harboring novel SaRI(msr) isolated from retail foods, indicating that this novel SaRI(msr) harboring mef(D)-msr(F) is distributed in food-related S. aureus in China and is one of the determinants for erythromycin resistance. The occurrence and propagation of similar mef(D)-msr(F)-carrying SaRI(msr) from S. aureus need further investigation.

• 单位
  广东省微生物研究所