Detection of Plasmid-mediated qnr Genes among the Quinolone Resistant Salmonella typhi from Patients Attending University of Abuja Teaching Hospital, Abuja, Nigeria

Aims: The aim of this study was to determine the presence of the qnr genes among S. typhi isolated from stool of patients with suspected typhoid fever, in University of Abuja Teaching Hospital, Abuja, Nigeria.

Study Design: Cross sectional study.

Place and Duration of Study: Department of Microbiology, Nasarawa State University, Keffi, between November 2022 and November 2023.

Methodology: Stool samples of patients with suspected typhoid fever were collected by standard methods in sterile disposable containers. After analysis of stool, microscopic observations and culture analysis, Salmonella typhi was isolated, antibiotic susceptibility testing was carried out, and the bacterial genome was extracted by boiling method. PCR for detection of qnr genes including qnrA, qnrB and qnrS was done by specific primers, then PCR products were run using gel electrophoresis and visualized by gel documentation system.

Results: Out of 150 isolates, 13 (8.7%) were positive for S. typhi. Antibiotic resistance among the isolates in decreasing order were as follows: imipenems (100.0%), cefuroxime (100.0%), cefotaxime (100.0%), nalidixic acid (92.3%), amoxicillin/ clavulanic acid (84.6%), ceftriaxone/sulbactam (84.6%), ciprofloxacin (84.6%), gentamicin (76.9%), levofloxacin (46.2%) and ofloxacin (46.2%). The most common antibiotic resistant phenotype was AUG- CTX-IMP-OFX-CN-NA-CXM-CRO-CIP-LBC at 30.4%. Multiple antibiotic resistance (MAR) was observed in 100% (13/13) of the isolates with the common MAR indices being 1.0 (30.8%), 0.7 (23.5%), 0.8 (23.1%) and 0.9 (15.4%). The only positive PMQR genes were qnrS and aac(6′)-Ib-cr with percentage occurrence of 50.0% respectively

Conclusion: The S. typhi isolates showed lower resistance to ofloxacin, levofloxacin, and gentamicin, and all isolates were MAR, with resistance to 10 antibiotics being the most predominant. In addition, qnrS resistance gene was the most common gene expressed.