Prevalence and gene sequencing of extended spectrum -lactamases producing Salmonella enterica serovar. Typhi from South-East Nigeria

Abstract

Enteric fever is a systemic disease classified into typhoid and paratyphoid fever. Fluoroquinolones and third generation cephalosporins are usually the drugs of choice in the management of Salmonella infections. Previous reports have indicated common occurrence of multi-drug resistance (MDR) including resistance to β-lactams and fluoroquinolones. However, there is paucity of information on the genetic determinants of resistance to β-lactam and fluoroquinolones from S. enterica in Southeast Nigeria. Salmonella enterica serovars were identified and screened (25 each from unrelated patients from the four hospitals). Resistant isolates were screened for ESBL phenotypically. Genomic and plasmid DNA were extracted by boiling and alkaline lysis, respectively. PCR amplification of blaTEM, blaSHV and blaCTX-M, among the ESBL positive isolates and sequencing of the Quinolone Resistance Determining Regions (QRDR) on fluoroquinolone resistant isolates were determined. Of the 100 isolates, thirty six of the MDR isolates produced ESBL phenotypically, of which 13 were blaCTX-M positive. DNA sequencing revealed single point mutations in gyrA at amino acid positions Asp-87-Gly, Asp-87-Asn and Ser-83-Tyr in 55 (68.8%), and double mutation in parC at positions Asp-87-Gly in 14 (17.5%). Mutations in gyrA, parC genes, and chromosomal blaCTX-M were responsible for the fluoroquinolones and cephalosporins resistance, respectively in some of the Salmonella enterica from Southeast Nigeria. QRDR of the gyrA gene of the isolates sequenced showed reduced susceptibility to some fluoroquinolone. The taxonomic and neighbouring trees of similar species causing infection worldwide were identified, and hence, alleviates the fear of easy spreading of quinolone and cephalosporin resistant isolates. Key words: Quinolone Resistance Determining Regions (QRDR), ESBL, S.enterica, mutation.