Molecular characterization of antimicrobial resistance in non-typhoid Salmonella from patients with bacteraemia admitted at the Aga Khan University Hospital

Abstract

In Africa, non-typhoid Salmonella (NTS) infections are common and selflimiting, however, they present life-threatening complications especially inchildren and adults who are immunosuppressed. In these individuals,antimicrobial treatment maybe required. The increasing antimicrobial resistancein NTS contributes to its spread and threatens the use of commonly available andclinically important antimicrobial agents. Over the last decade or more, resistanceto commonly available antimicrobials including ampicillin, cotrimoxazole,streptomycin, chloramphenicol and tetracycline rose remarkably.This study used 116 culture confirmed isolates of NTS from bacteremicpatients admitted in the medical ward of Aga Khan University Hospital, examinedover a 12-month period, 2007. NTS isolates were identified by culture methods,and confirmed by slide agglutination tests according to Kauffmann-White schemeutilizing the Salmonella poly-O, H1 and H2 agglutination antisera. Antimicrobialsusceptibility tests were done using the disk diffusion method. Conjugationexperiment was done to determine genetic basis of resistance and polymerasechain reaction was done to detect presence of genes encoding the quinoloneresistance-determining region.Resistant isolates contained plasmids of various sizes. Some isolates hadonly one plasmid while others had up to five plasmids of varying sizes. The largeplasmids extracted ranged from 90 kb to slightly over 147 kb in size; while thesmall size plasmids ranged from about 2.1 kb to 5.6 kb. The isolates that hadplasmids all had a 43.5kb plasmid size. Some isolates in Salmonella serotype groupB and group C3 had the largest plasmid size, slightly above 147 kb. The gyrB, parCand parE had 500bp products.The resistance to ampicillin, tetracycline, cotrimoxazole andchloramphenicol was low, but there was an increase in quinolone andfluoroquinolone antimicrobials.The study concluded that, there is a decrease in resistance to conventionaldrugs of choice for treatment of invasive NTS in Kenya, but there is an increase inresistance to quinolone and flouroquinolone; and a new resistance to cefotaximeand ceftriaxone.