Heavy metal loading of wetlands around lake victoria in Uganda and its implications to antibiotic resistance in environmental E. coli

Abstract

The effect of heavy metal loading on wetlands to the build up of antibiotic resistance among bacteria (pathogenic and environmental) in the Northern part of Lake Victoria within Uganda was carried out using Escherichia coli isolated from polluted and non-polluted sites. The main goal of this study was to assess the likely risks of anthropogenic and industrial activities to human public health and their impact on environmental microbiota in the region, but more so to determine ‘hotspot’ areas of antibiotic resistance and the antibiotics highly affected. A total of 28 E.coli strains were isolated from 36 sediment samples picked from wetlands in three towns of Kampala, Jinja and Busia at a rate of 12 samples per locality. Preliminary identification of the isolates was based on colonial morphology of the organisms on Chromocult agar (Merck, Germany), whereas confirmatory identification was by the conventional biochemical tests as according to Forbes et al. (1998). Antimicrobial resistance patterns of the isolates were determined using the single disc diffusion method (Bauer et al., 1966) and results interpreted according to the National committee for Clinical Laboratory Studies (NCCLS, 2000). The concentration of heavy metals was determined using the Atomic Absorption Spectrophotometry (AAS) technique as according to Schramel et al. (1982) and the Dutch standards, NEN 6465. Kampala had the highest incidence of antibiotic resistance, 26.2 % (n = 28), followed by Jinja (22.1%) and lastly Busia (2.9%). On average, ampicillin, a semi-synthetic penicillin was the most resisted, 35.7 % (n = 28) in the region. It was followed by co-trimoxazole, 32.1%, tetracycline, 28.6%, nalidixic acid and chloramphenicol, 21.4% and ciprofloxacin, 3.6%. Resistance to gentamycin (0.0%) was not exhibited at all. In Kampala, 7 (58.3 %) of the 12 isolates from this locality were multi-drug resistant (MDR), while 5 (45.5 %) of the 11 in Jinja had the same multi-drug problem. There was however no multi-drug resistance indicated from Busia. Of the 36 samples picked, 12 (33.3%) had elevated levels to heavy metals, with Kampala contributing the biggest percentage of 10 (27.8%), Jinja and Busia providing only 5.6% and 0% respectively. In Kampala, 10 (83.3%) of the 12 sampling spots had high levels of heavy metals, whereas Jinja had only 2(18.2%) and Busia 0% of the sites showing heavy metal pollution. Lead was the biggest heavy metal pollutant, followed by chromium, zinc, cadmium copper, nickel and lastly cobalt. There were however, no detectable levels of manganese above normal values in all the samples.There appeared a close relationship between antibiotic resistance and heavy metal concentration levels in the wetlands, as areas/spots with high figures of heavy metal pollution had correspondingly higher percentage of antibiotic resistant E.coli, compared to the non- polluted areas. Results also indicate a significant build up of resistance by E.coli to drugs that are routinely used in medical and veterinary practice in the region. However, resistance to ciprofloxacin (3.6%) and gentamycin (0.0%), both second line drugs for the treatment of gastroenteritis and some other disease conditions was insignificant. The study indicates a potential of wetlands in the region of providing a horizontal gene pool and exchange platform of resistance determinants to pathogens under the influence of heavy metals.