Comprehensive Molecular Profiling of AcrAB-TolC Efflux Pump Genes in Salmonella typhi Isolates from Typhoid Infected Patients.

Abstract

Salmonella typhi is a facultative anaerobic, rod-shaped, Gram-negative bacterium that causes typhoid fever, a potentially fatal systemic infection. This study aimed to characterize antibiotic susceptibility patterns, mutations at the molecular level, and efflux pump genes in clinical isolates. In this study, blood samples (n = 2950) were collected from suspected typhoid-infected patients, and 380 (12.88%) bacterial isolates were found, comprising 144 (37.89%) Gram-positive and 236 (62.10%) Gram-negative bacteria. S. typhi was identified in 95 isolates (25%), corresponding to an overall prevalence of 3.22%. Biochemical identification was performed by Analytical Profile Index (API) 20-E strips, and molecular identification was done by partial 16S rRNA gene using PCR. The S. typhi isolates were categorized into multidrug-resistant (MDR), 13 (13.68%), and extensively drug-resistant (XDR), 82 (86.31%), and their resistance patterns were recorded. Ampicillin (98.94%) and chloramphenicol (93.68%) showed the highest antibiotic resistance profiles, while azithromycin and meropenem exhibited no resistance. Numerous mutations were found in acrA, acrB, and tolC genes after sequencing; TolC (MDR) showed the highest score (16 points), and AcrB (MDR) displayed the lowest score (9 points). I-Mutant 2.0 was used to assess mutations and calculate the reliability index (RI), whereas trRosetta and Discovery Studio were used to predict and refine 3D protein models. Consensus sequences of the selected genes were analyzed to construct phylogenetic trees illustrating evolutionary relationships with other Salmonella enterica serovars. The study emphasizes the concerning multidrug resistance of S. typhi isolates as well as notable mutations (genetic changes) that may affect efflux pump activity and contribute to resistance.