Microbial and physico-chemical quality of some surface water resources in Durban, South Africa.

Abstract

Microbial and chemical contamination of inland and coastal waters in Southern Africa is a major challenge facing the water industry and regulatory authorities. Increased stresses on these surface water resources through human and environmental influences have resulted in deteriorating water quality that has severely encumbered the country’s capability to provide sufficient water to meet its needs and to ensure environmental sustainability. In addition, indiscriminate use of antibiotics has resulted in widespread contamination of surface waters, leading to accelerated development of antibiotic resistance and proliferation of resistant water-borne diarrhoeal-related pathogens, such as Escherichia coli and Vibrio cholerae. Despite the high level of contamination of South African surface waters, the microbiological quality of rivers and beaches in Durban, South Africa, have not been adequately investigated. Therefore, the current study assessed the seasonal fluctuations of the microbial and physicochemical quality of two rivers (Umgeni River and Umdloti River) and six beaches (Virginia Aerodome, Beachwood, Umgeni South, Battery, Sunkist, Addington) in Durban, using several bacterial indicator organisms and physico-chemical parameters as indices. The antibiotic resistance profiles (ARPs) of E. coli and V. cholerae strains, recovered from the water samples, were determined and changes in the microbial community of the water samples were monitored over a seasonal cycle, using denaturing gradient gel electrophoresis (DGGE). Spatial and seasonal fluctuations of the physico-chemical parameters differed significantly (p < 0.05) among the water samples with high heavy metal concentrations detected across the seasonal cycle. Temperature profiles ranged from 13°C to 26.5°C for the Umgeni River, 13°C to 27°C for the beaches and 12°C to 26°C for the Umdloti River while pH ranged from 6.30 to 8.45 (Umgeni River), 6.37 to 8.30 (beaches) and 5.96 to 7.94 (Umdloti River). Turbidity ranged from 0.53 NTU to 15.6 NTU (Umgeni River); 0.57 NTU to 2.37 NTU (beaches) and 2.23 NTU to 18.8 NTU (Umdloti River). During spring and summer, all river and beach water samples had < 500 μg/L phosphate concentrations; however, these concentrations increased significantly (p < 0.05) during autumn and winter in both rivers. Majority of the samples had low concentrations of ammonia and nitrates. Sulphate concentrations for the beach samples ranged from 2355 mg/L (B5 – summer) to 2899 mg/L (B2 – winter) as compared to the Umgeni and Umdloti Rivers which ranged from 3.90 mg/L (A4 – autumn) to 2762 mg/L (A1 – summer) and 4.47 mg/L (C4 – winter) to 168 mg/L (C1 – winter), respectively. According to the South African Target Quality Range guidelines for the heavy metals (in surface waters), all river and beach water samples exceeded the set limits for lead (Pb2+), mercury (Hg2+) and cadmium (Cd2+) across all seasons. During spring and summer all water samples complied with the aluminium guideline of 0 – 0.15 mg/L. Bacterial population profiles indicated that all sampling points failed to comply with the set guidelines (domestic use) for presumptive total coliform (TC), faecal coliform (FC) and total heterotrophic bacterial (THB) counts during all four seasons. Estimated TC, FC and THB populations as high as 8.6 x 101, 3.7 x 101 and 2.15 x 105 cfu/100ml, respectively, were obtained for some of the samples with peak indicator levels and generally a higher microbial load observed during the summer season. High prevalence of resistance to ampicillin [67.82% (Umgeni River)] was encountered among the E. coli isolates from the water samples followed by amikacin [53.33% (Umdloti River)], augmentin [49.6% (Umdloti River)], tetracycline [42% (Umgeni River)], streptomycin [37.1% (beaches)] and cotrimoxazole [33% (Umgeni River)]. The most frequently encountered form of resistance among the V. cholerae isolates was against cotrimoxazole [93.34% (Umgeni River)], streptomycin [84% (beaches)], erythromycin [78.7% (Umgeni River)], trimethoprim [77.7% (Umdloti River)], rifampicin [70% (Umgeni River)] and cefoxitin [45% (Umdloti River)]. Multidrug resistance among the E. coli isolates was indicated by twenty nine (Umgeni River), twenty six (beaches) and fourteen (Umdloti River) different resistance patterns, while the V. cholerae isolates produced eighteen (Umgeni River), thirty five (beaches) and twenty nine (Umdloti River) different resistance patterns. In addition, proportional resistances of the E. coli and V. cholerae strains to the different classes of antibiotics ranged from six to eleven and four to eleven different antibiotic classes, respectively. The present study suggests that the bacterial communities detected in the water samples collected from the rivers and beaches in Durban, followed seasonal dynamics and could possibly be the consequence of fluctuations in certain environmental factors. A total of 87 different DGGE bands were detected among the Umgeni River water samples, 127 different DGGE bands among the six beach water samples and 107 bands in the Umdloti River samples, over the four seasons. Twenty one dominant bands were found among all sampling sites, indicating widespread phylotypes, whereas 14 bands were exclusively detected at only one sampling site (C1) potentially indicating unique phylotypes. Some bands appeared all year-round, whereas some other bands were specific to a particular season. Overall, the present study successfully demonstrated the poor microbiological quality of the investigated river and beach water resources which raise concerns over the management of these water resources and the subsequent deleterious effects these waters could have on the end users. This emphasizes the need for implementation of improved management strategies of these river catchments and beaches for continued sustainability. Furthermore, the high level of multi-antibiotic resistance demonstrated by the E. coli and V. cholerae strains, recovered from the water samples, reiterates the need to continuously monitor the changing trends in antimicrobial resistance patterns of these diarrhoeal-related bacterial pathogens. Therefore, continued surveillance of these surface waters used for recreational or domestic purposes and development of adequate prevention strategies are needed for public health reasons. Lastly, combining the use of conventional faecal indicators with molecular-based techniques, such as DGGE, can provide more information on the microbial load and diversity of surface waters. In addition, information regarding the effects of seasonal variations on microbial diversity as observed in this study is important for the sustainable management of surface water resources.