Prevalence of multiple drug resistance and screening of enterotoxin (stn) gene in Salmonella enterica serovars from water sources in Lagos, Nigeria

Abstract

Objective: To determine the prevalence, antibiotic resistance and carriage of enterotoxin (stn) gene among strains of Salmonella isolated from water sources in Lagos.

Study design: A total of 200 samples (60 well water, 60 pipe-borne water and 80 different brands of sachet water) were collected at random from various locations in Lagos.

Methods: The samples were evaluated bacteriologically using standard methods. The identified isolates were subjected to antimicrobial susceptibility tests and were further screened for the presence of stn gene using standard procedures.

Results: Thirty-seven of the samples analysed were positive for Salmonella isolates. Seven serotypes were found -Salmonella typhi (n = 3, 8.1%), Salmonella typhimurium (n = 8, 21.6%), Salmonella choleraesuis (n = 5, 13.5%), Salmonella enteritidis (n = 9, 24.3%), Salmonella paratyphi (n = 8, 21.6%) and Salmonella arizonae (n = 4, 10.8%) - with at least one serotype present in all water sources. Over 60% of Salmonella isolates carried stn gene and the risk was higher in pipe-borne water. There was no relationship (P > 0.05) between enterotoxin-producing gene and antibiotic resistance in Salmonella isolates. Thirteen resistance patterns were exhibited by the isolates, with Str. Amp.Tet.Chl.Amo.Gen, Str. Amp.Tet.Amo.Chl.Amo.Nal.Nit, Str.Tet and Str. Amp.Tet.Chl.Amo being the most notable resistance patterns observed. Isolates that carried stn gene developed resistance to more antibiotics. Although reduced susceptibility to ciproflocacin was observed in two strains, none of the isolates developed resistance to ofloxacin.

Conclusion: Emerging multidrug-resistant Salmonella serotypes with stn gene were found in the water samples, which may pose a threat to public health. Constant monitoring of pipe leakages, the quality of various wells and the quality of sachet water is advocated to avoid possible future outbreaks of salmonellosis due to consumption of contaminated water.