Antimicrobial Susceptibility and Plasmid Profiles of Salmonella typhi isolated in Abuja, Nigeria.

Sixty clinical Salmonella spp. isolates were obtained from various health establishments in Abuja, Nigeria. These isolates were characterized using cultural, biochemical and serological assays. Antimicrobial susceptibility and plasmid analysis were used to determine the presence of plasmid-mediated multi-drug resistance. Each isolate was evaluated for susceptibility to ampicillin, chloramphenicol, gentamicin, tetracycline, cotrimoxazole, nalidixic acid, ciprofloxacin and afloxacin, using disk diffusion technique. Plasmid DNA was extracted by alkaline lysis method and fragments separated by electrophoresis on 1% agarose gel. DNA bands were visualized using ultraviolet light transilluminator and molecular weights determined. Plasmid transfer by mating was also performed using Escherichia coli K-12 as recipient. In total, 36 (60.0%) isolates were confirmed to be Salmonella typhi, of which 6 (16.7%) were fully susceptible to all microbial agents tested, while 7 (19.4%) were resistant to three or more antimicrobials including ampicillin, chloramphenicol, tetracycline, nalidixic acid and cotrimoxazole, categorized as ‘first line' drugs in the treatment of typhoid fever. However, all isolates evaluated were susceptible to ciprofloxacin and ofloxacin. Of the seven multi-drug resistant strains, 6 (85.7%) possessed plasmid sizes of 4.7 – 5.7 kilobase, suggesting that transmissible R-plasmids might be responsible for the drug resistance observed in Salmonella typhi strains in this study. Our findings show that plasmid-bearing multi drug resistant strains account for a reasonable percentage of Salmonella typhi isolates in Abuja, Nigeria. Keywords: Salmonella typhi, Plasmid, Antimicrobial resistance, typhoid fever. Journal of Medical Laboratory Sciences Vol. 14 (2) 2005: pp. 46-5