Investigation of faecal pollution and occurrence of antibiotic resistant bacteria as a function of a changed environment
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Worldwide, rapid industrialization and urbanization results in excessive release of pollutants into the water resources and the decline in water quality of rivers passing through these urban areas is well documented. Few studies have been conducted to assess physico-chemical and microbial quality of fresh water resources passing through urban areas in South Africa. Currently, not enough is known about the physico-chemical and microbial quality of the water resources in the North-West Province. However, human disturbances resulting from increasing urbanization in this Province is causing faecal pollution of the aquatic environments and ultimately degradation of stream biological integrity. A motivation for this study was the increasing concern of the possible link between faecal pollution gradients due to urbanization and development of bacterial resistance to antimicrobial agents. Such a study has not been conducted before. The aim of this study was to investigate the levels of faecal pollution and occurrence of antibiotic resistant bacteria in the Mooi River system as a function of a changed environment. Defined urbanization gradients were used as focal points. Eight sites along the Mooi River system were selected and monitored monthly for 1 year. Three samples per site were collected from the pre-determined sites along the Mooi River system from the Klerkskraal Dam to the North (site l) and several points along Mooi River passing through Potchefstroom to points on the southern side of Potchefstroom before Mooi River enters the Vaal River. River water samples were subjected to physico-chemical analyses and faecal indicator bacterial levels were determined. Faecal coliforms to enteroccoci levels were used to determine the ratio between these groups. Results indicated seasonal and locational variation in most of the physico-chemical parameters and faecal indicators studied. Rainfall was an important factor which strongly influenced the characteristics of these parameters. Also temperature, pH and rainfall influenced the elevated levels of the microbiological indicators observed. High levels of the faecal indicator bacteria were observed in the Potchefstroom urban area when compared to upstream and downstream river segments. Levels of heterotrophic plate count bacteria were such that no marginal and log differences were observed or enumerated on media without and with ampicillin. Results of faecal coliform to enteroccoci ratio suggested that non-human sources contributed greater towards faecal pollution. River water isolates of faecal coliform and enteroccoci from the Potchefstroom sites exhibited resistance to multiple antibiotics. More than 60% of enteroccoci were resistant to at least 4 antibiotics and between 60-80% of the faecal coliform were resistance to 6 antibiotics. Some isolates were resistant to as many as 10 antibiotics. Among the 6-group MAR indices, highest indices were indicated for the Potchefstroom urban area (0.32 for faecal coliform and 0.28 for enteroccoci). Cluster diagrams based on antibiotic inhibition zone diameter data were constructed. The purpose was to establish whether there were isolates from different sites with similar antibiotic exposure histories. Faecal coliform cluster analysis revealed patterns of association between Potchefstroom, downstream and upstream isolates. Enteroccoci cluster analysis could not clearly resolve differences between samples from different sources. However, urban-rural gradients were recognized in terms of faecal indicator bacteria such total coliform, faecal coliforms and enterococci and also in terms of MAR index. The antibiotic resistance technique used in this study proved a valuable tool to study impacts of urbanization on associated water resources. It is however advised that the study period be extended over a two year period in order to gain sufficient data, and also because micro-organisms show seasonal fluctuations with respect to numbers and species.