Drinking water quality along the distribution network and associated antibiotic resistance in Maun, Botswana

Abstract

Maintaining the water quality in the distribution system is crucial to supplying safe drinking water to consumers. The main aim of the study was to analyse physicochemical, bacteriological parameters and investigate prevalence of antibiotic resistant bacteria and their antibiotic resistance genes in the drinking water distribution system in Maun, Botswana. Forty-four water samples were collected at different season interval and were tested for chlorine and turbidity and the results showed that in May, September, January and March, turbidity and chlorine measured 1.0 NTU (0.2 mg/L), 1.1 NTU (0.5 mg/L), 1.0 NTU (0.2 mg/L), 2.7 NTU (0.1 mg/L) respectively. The indicator organisms recorded were heterotrophic bacteria (37.7 %), total coliforms (28 %), Faecal streptococci (18.9 %) while Escherichia coli was at 10.4 % and 5 % for unusual isolates. Antibiotic susceptibility tests were performed on 150 isolates, which were tested against 15 different antibiotics using the Kirby-Bauer diffusion test. Ninety-two percent of the isolates were susceptible to at least one antibiotic and only one isolate (121-S5; E. coli) showed resistance to all the antibiotics used. For multi-drug resistance (MAR) patterns, the most prevalent antibiotic resistance pattern observed was AMP-AML-MEL-C-W-RD-TET-PENSTREP. In addition, 92 % of the isolates were susceptible to meropenem followed by gentamicin (88 %) and ciprofloxacin (81 %). The amplified 16S rDNA sequences were successfully used to identify the 10 selected isolates. The presence of targeted ARGs (tetA, tetB, int1, strepB and sul1) for both culture isolates and whole sample genome were established. Moreover, metagenomic analysis confirmed the presence of some pathogenic bacteria such as Mycobacterium tuberculosis, Legonillela sp, Cholera sp, Staphylococcus sp, Sphingosinicella sp. and Pseudomonas sp. In conclusion, the results indicated the occurrence of indicator bacteria and other non-culturable species in the drinking water as the water moves from the treatment plant to lines that feed the consumers. The results also signified the presence of antibiotic resistant bacteria and their resistance genes in the water samples. The data obtained may be thereof useful in monitoring the integrity of the water quality in the distribution network after treatment.