Abstract

Objective: This study aimed to determine the antibiotic resistance profiles and the phenotypic and genotypic activities of extended-spectrum β-lactamases (ESBLs), AmpC, and carbapenemases in bacteria isolated from water samples collected from the Kızılırmak River.

Methods: Water samples were collected aseptically from 10 different sites along the Kızılırmak River. Bacteria isolated by membrane filtration and identified using conventional methods were tested for antibiotic susceptibility by the disk diffusion method. The phenotypic and genotypic activities of ESBLs, AmpC, and carbapenemases in bacteria belonging to the Enterobacteriaceae family were determined using phenotypic methods and conventional polymerase chain reaction (PCR), respectively.

Results: The identified isolates included 2 Escherichia coli, 6 Klebsiella aerogenes, 10 Aeromonas hydrophila, and 2 Mannheimia haemolytica. Among the 8 Enterobacteriaceae isolates, resistance rates were highest for cefoxitin, amoxicillin, amoxicillin-clavulanic acid, and ampicillin (100% each), followed by cefotaxime (12.5%). Resistance to ciprofloxacin and ceftazidime was detected in 10% of A. hydrophila isolates, whereas 100% of M. haemolytica isolates were resistant to amoxicillin-clavulanic acid, nalidixic acid, and tetracycline. Phenotypically, 100% resistance to cefoxitin and, consequently, 100% AmpC activity were detected, whereas 100% susceptibility to meropenem and no carbapenemase activity were observed. According to the rapid antimicrobial susceptibility testing (RAST) procedure, no ESBL activity was detected in E. coli isolates, whereas 5 K. aerogenes isolates were positive for ESBL activity by the combination disk test (83.3%). Genotypically, the ESBL genes TEM and CTX-M-9 were detected at 100%, CTX-M-1 and OXA-1 at 87.5%, and SHV at 75%; the AmpC-associated FOX gene was detected at 87.5%. No carbapenemase genes (NDM, KPC, VIM, IMP, or OXA-48) were detected, consistent with the phenotypic findings.

Conclusion: The high levels of antibiotic resistance observed in bacteria isolated from the Kızılırmak River suggest that the river ecosystem may serve as a significant reservoir of resistant bacteria. Considering human, animal, and environmental interactions within the One Health framework, ongoing monitoring of environmental antimicrobial resistance and implementation of control measures are warranted. The preserved susceptibility to carbapenems was an important favorable finding.