Antibacterial Resistance Profile and PCR Detection of Antibiotic Resistance Genes in Salmonella Serovars Isolated from Blood Samples of Hospitalized Subjects in Kano, North-West, Nigeria

Aim: The aims of the study were to determine the antibacterial resistance profile and detect the presence of antibacterial resistance genes of Salmonella isolates recovered from the blood samples of hospitalized subjects in Kano metropolis.

Study Design: The study is a descriptive cross-sectional study.

Place and Duration of Study: One milliliter of venous blood was collected from each patient with some or all clinical features of salmonellosis that sign a consent form and transfer into EDTA bottles. If daily is unavoidable blood samples were stored at 4°C. Samples were analyzed at the both Laboratories of the authors. This work was carried out between May, 2011 and March, 2013.

Methodology: The blood specimens were cultured in thioglycollate broth and sub-cultured onto deoxycholate citrate agar (DCA), Salmonella-Shigella agar (SSA) and brilliant Green agar (BGA) followed by confirmation of presumptive colonies using different biochemical tests and analytical profile index 20E. Serologic identification of Salmonella was performed by slide agglutination test using polyvalent O and H Salmonella antisera. Antibacterial drug susceptibility studies were performed by the disc diffusion method using ampicillin, chloramphenicol, ciprofloxacin, nalidixic acid and Trimethoprim-sulfamethoxazole. Out of one hundred and four salmonellae isolates obtained in this study, twenty one were subjected to DNA extraction, real-time and multiplex polymerase chain reaction (PCR) using various primer sets targeting the specific sequences of the resistance genes.

Results: Of the 104 isolates 96 (92.3%) were resistant to Ampicillin; 81 (77.9%) resisted to Nalidixic acid; 30 (30.8%) resisted to Chloramphenicol, 17(16.3%) resisted to Cotrimazole while none (1.0%) resisted to Ciprofloxacine. Among the thirteen Salmonella isolates tested by real-time PCR, Tem gene was detected with a higher frequency (38.5%) compared to the gyrB gene (30.8%). In addition, four Salmonella isolates were found to harbour both tem and gyrB genes together with 30.8%. In this study, no gyrA gene amplicon was obtained, although one Salmonella Typhi strain was resistant to ciprofloxacin phenotypically. There was significant correlation between the presence of tem and/or gyrB and resistance to ampicillin and nalidixic acid. However, in this study, out of the eight Salmonella isolates tested by multiplex PCR technique, sul2 gene was detected in two (25.0%) isolates and catP gene was detected in one (12.5%); while the amplification of these two genes failed in five Salmonella isolates (62.5%) and no isolate harboured both sul2 and catP genes. There is no significant correlation between the presence of sul2 /catP and resistance to chloramphenicol and cotrimoxazole.

Conclusion: Most Salmonella serovars isolated from patients in Kano, Nigeria resisted to Ampicillin. They also resisted to Nalidixic acid, Chloramphenicol and Cotrimazole, in decreasing order. Ciprofloxacine remained effective against all the Salmonella isolates tested. Almost all the genes tested were circulating within Kano metropolis, including tem, gyrB, sul2 and catP genes with exception of gyrA. There was only significant correlation between the presence of tem and/or gyrB and resistance to ampicillin and nalidixic acid.