Rapid detection of fluoroquinolone-resistant Staphylococcus epidermidis and its associated mutations in the quinolone resistance-determining region.

The purpose of this study was to investigate the relationship between amino acid mutations in the quinolone resistance-determining region (QRDR) of Staphylococcus epidermidis and its susceptibility to fluoroquinolones, as well as the potential of single nucleotide polymorphism (SNP) genotyping for rapid detection of resistant strains. Thirty-three S. epidermidis strains were analyzed (25 from preoperative patients, 8 from keratoconjunctivitis patients). Minimum inhibitory concentrations (MICs) of fluoroquinolones were determined using the broth microdilution method. The QRDR sequences of resistance-related genes (gyrA, gyrB, parC, parE) were analyzed by direct sequencing. SNP genotyping was performed using TaqMan probes targeting conserved regions and mutation sites. The correlation between fluoroquinolone use and mutation counts was analyzed using the Mann-Whitney U test and Spearman's rank correlation test. Fifteen strains showed resistance to fluoroquinolones. Mutations in gyrA, parC, and/or parE were detected in 15 fluoroquinolone-resistant strains. Double mutations in both gyrA and parC were associated with the strongest resistance. Among the 18 non-resistant strains, 17 had no mutations, while one strain had a mutation in parE (Asn404Ser). No mutations were found in gyrB. A significant difference in mutation presence was observed between fluoroquinolone-use and non-use groups (p = 0.026). Additionally, a positive correlation was found between fluoroquinolone use duration and mutation counts (p = 0.025). SNP genotyping was accurate for all strains and successfully identified mutations in gyrA, parC, and parE. The duration of fluoroquinolone use influences mutation counts in the QRDR sequences. Additionally, SNP genotyping is a rapid and effective method for identifying fluoroquinolone-resistant S. epidermidis strains.