Investigation into the bacterial pollution levels at various sites along the Diep and Plankenburg river systems, 3 Western Cape, South Africa

This study sought to investigate and compare bacterial contamination levels at six different sites along the Diep and Plankenburg river systems in the Western Cape, South Africa. Surface water and sediment samples were collected monthly from the six selected sampling sites along both river courses between January 2014 and December 2014 and were evaluated for bacterial contaminants. Microbial isolation, characterisation and identification were done using conventional techniques (serial dilution, Gram staining, and biochemical testing) and molecular identification techniques (polymerase chain reaction and DNA sequencing). A total of 19 bacterial isolates belonging to the genera Raoultella, Bacillus, Pseudomonas, Klebsiella, Escherichia, Enterobacter, Exiguobacterium, Acinetobacter, Serratia, Aeromonas, Staphylococcus and Citrobacter were isolated from the surface water and sediment samples at the end of the survey. Higher microbial load was obtained from sediment samples compared to surface water samples. Seasonal variation was also observed in terms of microbial counts. Higher microbial counts were obtained during summer sampling time compared to winter sampling time. The most contaminated site was located on Plankenburg River with average bacterial counts ranging between 3.1 × 105–6.9 × 108 CFU/ml and 3.9 × 106–2.88 × 109 CFU/ml from surface water and sediment, respectively, recorded at this site during winter and summer. Although lower microbial counts were recorded along the Diep River course, most of the bacterial counts recorded along both rivers exceeded the acceptable maximum limits for river water.