Molecular Characterisation of Salmonella Species Isolated from Various Drinking Water Sources in Some Parts of Bauchi Metropolis, Nigeria

Abstract

Contamination of drinking water by pathogenic bacteria remains an important public health concern, particularly in communities that rely on multiple treated and untreated water sources. This study investigated the occurrence and molecular characteristics of Salmonella species isolated from selected drinking water sources in Bauchi metropolis, Nigeria. A total of 250 water samples were collected over six months from wells, boreholes, and tap water in Wuntin Dada, Jahun, Yelwa, and Bakin Kura. The samples comprised 165 well water samples, 55 borehole samples, and 30 tap water samples. Isolation and presumptive identification were carried out using standard microbiological procedures, including culture on selective media, Gram staining, microscopy, and biochemical tests. Molecular confirmation was performed using polymerase chain reaction targeting bacterial 16S rRNA and Salmonella-associated virulence genes, including invA and fliC, followed by agarose gel electrophoresis. Of the 250 water samples examined, 32 were positive for Salmonella species, giving an overall occurrence of 12.8%. Among the positive isolates, 21 were obtained from well water, 7 from borehole water, and 4 from tap water. The isolates showed typical morphological and biochemical features consistent with Salmonella species, including Gram-negative rods, pale colonies on MacConkey agar, black-centred colonies on Salmonella-Shigella agar, oxidase negativity, catalase positivity, citrate utilisation, and urease negativity. Molecular analysis detected target gene bands consistent with bacterial and Salmonella-associated markers in the tested isolates. The findings indicate that drinking water sources in the study area were contaminated with Salmonella species and highlight the need for improved water-source protection, routine microbiological monitoring, and effective water-treatment practices.