Genetic Characterization and Evaluation of Antimicrobial Resistance Patterns of Salmonella Typhi Isolates

Abstract

Salmonella is a genus of bacteria comprising a group of closely related organisms that are pathogenic to humans and other vertebrates and pose a global health problem. Infections in humans due to Salmonella serotypes result in typhoid fever and gastroenteritis. There is paucity of information regarding the strains circulating and their antimicrobial resistance profiles. Reports show that Salmonella increasingly undergoes resistance and shows a rapidly changing nature of antibiotic resistance patterns. Continual genetic characterization and drug resistance surveillance is required to evaluate their genetic structure and resistance profiles regarding specific antibiotics. Therefore, the aim of the present study was to genetically characterize and evaluate the antimicrobial resistance profile of isolates of Salmonella Typhi collected from Kenyatta National Hospital and Agha Khan University Hospital. A total of 205 stool samples were collected from Kenyatta National Hospital and Agha Khan Hospital from patients suspected to be suffering from typhoid fever. The samples were cultured in nutrient broth and subcultured on Xylose Deoxycholate agar to identify Salmonella colonies. Fifty samples showed Salmonella morphology and were subjected to biochemical tests. Biochemical characterization identified 33% of the isolates as Salmonella Typhi and 67% as other Salmonella spp. DNA was extracted and used for polymerase chain reaction (PCR) targeting 16S rRNA gene. The amplified products were sequenced and phylogenetic analysis based on the 16S rRNA gene sequences showed that the isolates clustered close to Salmonella Typhi strain CT18 and its plasmid pHCM1 associated with drug resistance. Antimicrobial susceptibility tests showed that 73% of the isolates were multiply resistant to the Aminopenicillin, Sulfonamide, Phenicol and Aminoglycoside classes of drugs. A resistance of 7% to 19% and an intermediate resistance of 19% to 50% were observed in the Beta-lactamase, Fluoroquinolone and Cephalosporin classes of drugs. The current high rate of multidrug resistance and the high probability of its rise calls for continual characterization and monitoring of drug resistance as well as proper regulation in the dissemination and use of antimicrobial drugs.