Prevalence of the cfr gene and co-dissemination with the fosD gene in swine-derived Staphylococcus aureus.

OBJECTIVE

Animal-derived Staphylococcus aureus frequently exhibits multidrug resistance, with complex and diverse resistance mechanisms that have raised significant public health concerns. The objective of this study was to determine the prevalence of S. aureus in swine farms and evaluate its antimicrobial resistance and distribution of oxazolidinone resistance genes.

METHODS

The swine samples were collected on 17 swine farms from four provinces in China. All S. aureus isolates were screened for cfr, optrA, and poxtA. Whole-genome sequencing of cfr-positive strains revealed their molecular characteristics. All cfr-positive isolates were subjected to antimicrobial susceptibility testing.

RESULTS

A total of 302 swine-derived S. aureus were collected from 4973 samples. Seven cfr-positive S. aureus strains, including four ST1-t4792 MSSA, two ST9-t4358 MSSA, and one ST398-t034 MRSA, were identified by whole-genome sequencing. Antimicrobial susceptibility testing against 23 agents from 12 classes revealed that all cfr-positive strains were resistant to penicillin, ampicillin, erythromycin, tetracycline, doxycycline, clindamycin, florfenicol, tiamulin, and valnemulin. Six MSSA strains additionally exhibited resistance to gentamicin, kanamycin, and ciprofloxacin, while three strains showed resistance to tilmicosin, ciprofloxacin, and trimethoprim-sulfamethoxazole. Third-generation sequencing of a strain co-harbouring cfr and fosD demonstrated that both genes were located on a plasmid also carrying fexA and aadD.

CONCLUSIONS

This study revealed the presence of the cfr gene across diverse multilocus sequence typing types of S. aureus and highlighted the co-dissemination of cfr with fosD and other resistance genes via plasmids in S. aureus. Based on One Health principles and risk of multidrug resistance spread, continuous surveillance of animal-derived S. aureus was urgently needed.