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Safdar Ali
Muhammad Rizwan
Maria Rasool
Rafia Anwar
Maimona Sadia
Irfan Ahmad
Areej Safdar
Laiba Qadir


Salmonella, Typhoid fever, Gene, qnrS


Introduction: Typhoid fever is caused by Salmonella typhi, which is known for being resistant to several antibiotics. It is one of the leading causes of death and infections in developing nations, and also a frequent cause of illnesses in Pakistan. The major cause of this infection is to face a significant challenge in dealing with higher-level quinolone-resistant S. typhi strains. To combat this challenge a study was designed to determine the presence of the qnr genes among S. typhi isolated from stool of patient samples.

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, S. 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 qnr AqnrB 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.

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