Investigation of fosfomycin resistance genes, CTX-M, SHV and TEM genes in e coli strains as the causative agent of urinary system i̇nfections

INTRODUCTION and OBJECTIVE: Urinary tract infections (UTIs) are among the most common bacterial infections, with a higher prevalence in women. Escherichia coli is the most frequently encountered causative agent of UTIs. The dissemination of uropathogenic E. coli (UPEC) strains producing extended-spectrum beta-lactamases (ESBLs) poses a challenge in the treatment of UTIs. Due to increasing antimicrobial resistance profiles, the use of antibiotics such as fosfomycin has regained importance. Fosfomycin is a broad-spectrum antibiotic that irreversibly inhibits the first step of peptidoglycan synthesis, acting as a phosphoenolpyruvate analogue. Fosfomycin resistance occurs through various mechanisms, including reduced permeability to fosfomycin, modifications in the target site MurA, and enzymatic inactivation. This study aims to investigate fosfomycin resistance genes in E. coli isolates obtained from urine samples. Since fosfomycin resistance genes are often found on the same plasmid as ESBL genes such as blaCTX-M, blaTEM, and blaSHV, the presence of beta-lactamase genes has also been examined in fosfomycin-resistant E. coli isolates. MATERIALS AND METHODS: The study included 97 E. coli isolates obtained from urine samples sent for culture to the Central Bacteriology Laboratory of Ankara City Hospital between June 2022 and February 2023, which exhibited resistance to fosfomycin as determined by the automated system (Vitek 2) or the disk diffusion method. Fosfomycin susceptibility was investigated for all isolates using both the disk diffusion and agar dilution methods. The antibiotic susceptibilities of the isolates were determined using an automated system. In fosfomycin-resistant isolates, fosfomycin resistance genes (fosA3, fosA, fosC2, fosX, fosB), and three beta-lactamase genes (blaCTX-M, bla TEM, blaSHV) were investigated using the polymerase chain reaction (PCR) method. RESULTS: A total of 97 E. coli isolates, determined to be resistant to fosfomycin using automated systems and/or the disk diffusion method. Out of these isolates, 52 were identified as fosfomycin-resistant using the automated system, while 45 were determined to be fosfomycin-resistant through the disk diffusion method. Using the agar dilution method, 72 out of 97 isolates were found to be resistant to fosfomycin. Among the 72 fosfomycin-resistant E. coli isolates, the blaCTX-M gene was detected in 40.2% (29/72), the blaTEM gene in 91.6% (66/72), and the blaSHV gene in 20.8% (15/72) of them. Among these isolates, 28 had both blaCTX-M and blaTEM genes, 13 had both blaTEM and blaSHV genes, and 4 had both blaCTX-M and blaSHV genes. In three isolates, all three genes (blaCTX-M, blaTEM, and blaSHV) were detected together. Furthermore, the fosA3 gene was found in 3 (4.2%) of the 72 fosfomycin-resistant E. coli isolates, while the fosA, fosC2, fosX, and fosB genes were not detected in any of the isolates. Among the three isolates carrying the fosA3 gene, two also had both blaCTX-M and blaTEM genes, while the remaining isolate only had the blaTEM gene. None of the three isolates had the blaSHV gene. CONCLUSION: The use of fosfomycin as an alternative drug in the treatment of multidrug-resistant infections, such as ESBL-positive UPEC, is recommended. Understanding the fosfomycin resistance mechanisms in strains producing ESBLs is important for guiding treatment and monitoring resistance. Further studies are needed to determine the predominant fosfomycin resistance profiles in our country. Keywords: UPEC, fosfomycin resistance, fos resistance genes, ESBL