Emergence of Third Generation Cephalosporin Resistance and Typing by Randomly Amplified Polymorphic DNA (RAPD) among Clinical Salmonella Isolates from Lagos, Nigeria

Aims: To investigate emergence of cephalosporin resistance and clonal relatedness among clinical Salmonella isolates recovered from patients in Lagos, Nigeria.

Study Design: It is an investigative study. A total of 300 patients who presented with various types of medical conditions at prominent referral public hospitals were recruited.

Place and Duration of Study: Department of Microbiology, Lagos State University, Ojo, Lagos and Nigerian Institute of Medical Research, Yaba, Lagos, Nigeria from July 2011 to May 2012.

Methodology: Salmonella identification was done using standard methods. The isolates were subjected to antimicrobial susceptibility by disk diffusion method. The isolates were further screened for plasmid DNA and blaCTX-M carriage on plasmid using alkaline lysis and PCR methods. Clonal relatedness of the isolates was assessed by RAPD PCR using genomic DNA as template for three RAPD primers (784, 1254 and OPA4). The resulting RAPD types were determined by visualization and discrimination index was measured using a discriminating index calculator.

Results: Sixty three Salmonella isolates were recovered made up of five serovars. In all 49% of the isolates were resistant to cefuroxime, 46% to cefoxitin, 37% to cefriazone and 35% to ceftazidine. Interestingly 28(87.5%) of the 32 ESBL producing Salmonella isolates possessed at least one or more plasmids from five distinct sizes recorded 2.5; 4; 9; 15;23.5kb. Four distinct RAPD profiles were exhibited by the test strains. The total discriminatory power among the isolates was 0.77 (77%).

Conclusion: Third generation cephalosporin resistance involving blaCTX-M has emerged among clinical Salmonella isolates in Lagos. RAPD elicits potential as a cost-effective and time saving tool for local discrimination of clinical Salmonella isolates for epidemiological purposes.