Molecular characterisation of Salmonella Enterica Serovars isolated at the Univerisity Teaching Hospital,Lusaka

Abstract

Salmonellaenterica species are important food-borne pathogens that cause gastroenteritis and enteric fever, and are responsible for a huge global burden of morbidity and mortality. In addition, Salmonellaenterica has been associated with multiple drug resistance and this complicates disease management. Since November 2010, Zambia has been experiencing a rise in the number of Salmonella infections but the antibiotic susceptibility pattern andmolecular epidemiologyremain unknown. Therefore, the main objective of this study was to determine the molecular characteristics of Salmonella enterica serovars isolated at the University Teaching Hospital in Lusaka, Zambia.This was a laboratory-based cross-sectional study on the molecular characterisation of Salmonella serovar obtained from the typhoid fever outbreaks. Antibiotic susceptibility testing was performed by the microbroth dilution method, and the presence of drug resistance genes were confirmed by Polymerase Chain Reaction and DNA sequencing. Additionally, Whole Genome Sequence Typing was performed to determine the genetic relatedness of Salmonella Typhi strains. Of the 127 Salmonella isolates analysed, 55.9% were Salmonella Typhi, 21.3% Salmonella Paratyphi B, 1.6% Salmonella Senftenberg and 21.3% were other non-typhoidal Salmonella. Multidrug resistance was alarmingly high, with 100% Salmonella Paratyphi B and Senftenberg, 85.9% Salmonella Typhi and 55.6% non-typhoidal Salmonellae exhibiting this trend.A fewSalmonella Typhi isolates (2.8%) were nalidixic acid-resistant and this was due to single mutations in the gyrA gene at codons Ser83 and Asp87. Thirty three randomly selected S. Typhi revealed that all but one, the pan-susceptible isolate harbouredstrA, strB, ΔaadA1and BlaTEM-1,sul1, sul2, catA1, dfrA7 and dfrA14 genes. Class 1 integron, harbouring an 800bp integron containing the dfrA7 gene, was detected in both Salmonella Typhi (29/44, 65.8%) and Salmonella Paratyphi B (22/27, 81.5%). Single Nucleotide Polymorphism analysis revealed a profound clustering among the isolates separating individual strains from the nearest neighbour with 2 to 62 single nucleotide polymorphisms.Phylogenetic analysis and deletion content clearly indicated that the Salmonella Typhi isolates involved in the outbreak were distantly related, suggesting that multiple clones and lineages were responsible for the outbreak. Hence regular monitoring and surveillance should be doneto prevent further emergence of drug resistance strains and spread of these global pathogen.