Molecular Identification of Plasmid-Encoded qnr Genes in Quinolone-Resistant Salmonella typhi from Patients at National Hospital, Abuja, Nigeria

Aims: The study aimed to investigate and document the presence of qnr genes in S. typhi isolated from stool samples of patients suspected of having typhoid fever at the National Hospital, Abuja, Nigeria.

Study Design: Cross sectional study.

Place and Duration of Study: Department of Microbiology, Nasarawa State University, Keffi, between October 2020 and April 2022.

Methodology: Stool samples from patients suspected of having typhoid fever were collected in standard sterile disposable containers. After stool analysis, which included microscopic examination and culture, Salmonella typhi was isolated. Antibiotic susceptibility testing was conducted on the isolates, and bacterial genomes were extracted using the boiling method. PCR with specific primers was used to detect qnr genes (qnrB, qnrA and qnrS). The PCR products were then analyzed by gel electrophoresis and visualized using a gel documentation system.

Results: Results showed that 6.6% (10/150) of samples were positive for S. typhi. Antibiotic resistance among the isolates was observed as follows, in descending order: imipenem (100.0%), cefuroxime (100.0%), cefotaxime (100.0%), nalidixic acid (90.0%), amoxicillin/clavulanic acid (90.0%), levofloxacin (80.0%), ceftriaxone/sulbactam (70.0%), ciprofloxacin (70.0%), gentamicin (70.0%), and ofloxacin (60.0%). The most prevalent antibiotic-resistant phenotype was AUG-CTX-IMP-OFX-CN-NA-CXM-CRO-CIP-LBC, observed in 20.0% of cases. Multiple antibiotic resistance (MAR) was detected in all isolates (10/10), with common MAR indices being 0.8 and 0.9 (30.0%). The only positive genes related to plasmid-mediated quinolone resistance (PMQR) were qnrA and aac(6′)-Ib-cr.

Conclusion: The S. typhi isolates exhibited significant resistance to all tested antibiotics, with all isolates demonstrating multiple antibiotic resistance (MAR), primarily resisting 9 and 8 antibiotics. Additionally, the qnrA resistance gene was the most frequently detected gene among them.