Emergence of Plasmid-mediated Quinolone-Resistant Salmonella Typhi Clinical Isolates from Punjab, Pakistan

The present study evaluated the prevalence of fluoroquinolone resistance and the underlying mechanisms among Salmonella Typhi clinical strains from Punjab, Pakistan. A total of 174 Salmonella Typhi strains were isolated from the blood culture samples. The strains identification was done by using the API 20E system and VITEK®, while serovar validation was done by agglutination assays using antisera. Molecular characterization was done by PCR using the primers targeting the fliC-d gene of Salmonellaenterica serovar Typhi. Antimicrobial susceptibility testing was performed by disc diffusion procedure and the minimum inhibitory concentration using the broth microdilution technique. Moreover,plasmid-mediated quinolone resistance genes were amplified through a polymerase chain reaction. Alarming rate of ciprofloxacin resistance (90.8%) were observed with high MICs ranging from <0.06 µg/mL to > 2.0 µg/mL.Overall, the qnrS gene was detected among every ciprofloxacin-resistant isolate, of which maximum frequency of qnrS genes was detected among isolates showing MICs <1.0 µg/mL, while 14 qnrSgene-positive isolates were showing very high MICs values 2.0 µg/mL.Moreover, the ciprofloxacin-resistantisolates, as well as the ten isolates showing intermediate resistance (MIC; 0.5 µg/mL), were negative for qnrA and qnrB genes. This study highlights that the quinolone resistance among S. Typhiis at a critical level that necessitates the need for alternative therapeutic measures and the development of new antibiotics.