Analysis of GyrA gene mutations in environmental Escherichia coli: understanding the mechanisms and spread of quinolone resistance in ecosystems.

The spread of antimicrobial resistance to antibiotics has emerged as a global health threat to contemporary medical practice. Among the various antibiotic-resistant pathogens of concern, fluoroquinolone-resistant Escherichia coli has been increasingly detected in environmental reservoirs. The present study investigates the molecular screening of the gyrA gene in E. coli isolates derived from various environmental sources, focusing on the identification and genetic analysis of mutations in the Quinolone Resistance-Determining Region. In this study, antimicrobial susceptibility testing was initially performed on 50 non-duplicate E. coli isolates collected during the study period. Among these, only 10 isolates exhibited phenotypic resistance to the antibiotics of interest, while the remaining 40 were fully susceptible. Because the primary objective of the work was to characterize resistant strains in detail, subsequent analyses were restricted to these 10 resistant isolates, which explains the final sample size presented for resistance-related results. DNA was extracted and was confirmed by 16 S rRNA gene sequencing. The gyrA gene was amplified and sequenced to detect mutations associated with quinolone resistance. About 8 specific mutations were identified in most of the samples and correlated with the quinolone susceptibility profiles of each isolate, which were determined using Kirby bauer disk diffusion method for a range of antibiotics. Our results revealed a significant prevalence of QRDR mutations, especially at the 248th (Ser-83) and 259th (Asp-87) positions in gyrA gene, which were strongly associated with increased resistance to quinolones. These findings highlight the need for vigilant use of fluoroquinolones to mitigate the spread of microbial resistance.