Characterization of Clostridium, Aeromonas and heterotrophic bacteria in selected groundwater systems

Abstract

Water sources in the North West Province (NWP) are made up of groundwater, surface water and re-useable effluent. However, major water challenges are experienced in the NWP when quality and quantity are considered. The NWP is regarded a water stressed Province, due to its limited water sources. Communities in the NWP rely greatly on ground and surface water for their water provision. Urban areas such as Mahikeng, Lichtenburg, and Coligny rely solely on groundwater. In these regions, groundwater undergoes partial purification treatments. However, communities in rural areas and informal settlements use groundwater untreated. This Province is also known for its great participation in agriculture because of its rich production in crops such as maize, sorghum and sunflower. This also requires a great quantity of water, hence stressing available water sources even more. The aim of this study was to characterize Clostridium sp., Aeromonas sp. and heterotrophic count bacteria in selected groundwater systems in the NWP. During the course of this study, groundwater was obtained across three seasons: winter, summer and autumn. Groundwater temperature fluctuated between the seasons, with the lowest and highest water temperatures observed during summer autumn, respectively. The pH of the groundwater systems was relatively neutral throughout the seasons. However, parameters such as TDS, salinity as well as CODs were exceptionally high in all seasons. Chemical parameters such as nitrates and phosphates were observed in low concentrations in all seasons. The identification and characterization of Clostridium sp., Aeromonas sp., and HPCs was achieved utilizing culture-based methods. A total of 91 isolates were enumerated and identified using 16S rRNA PCR and sequencing. HPCs were observed in high levels with Bacillus being the most predominant HPC species seen across all three seasons. Other species of concern that were identified include Citrobacter sp. and Escherichia sp. Furthermore, Clostridium sp., and Aeromonas sp. were found present in the groundwater systems during summer, however at very low levels. Three Clostridium species (C. perfringens, C. sordellii and C, tepidum) and a single Aeromonas species (A. hydrophila) were identified in this study. Out of all isolates obtained, 80% were beta-hemolytic while 70% of the HPCs were positive for DNase production. Ninety percent of the Aeromonas species were positive for gelatinase production whilst none of the isolated microorganisms tested positive for lecithinase production. The production of extracellular enzymes in microorganisms is a clear indication that they could be regarded as opportunistic pathogens. The antibiotic resistance patterns of the isolated microorganisms was achieved using the Kirby-Bauer Disk diffusion method. Aeromonas sp., and HPC species were exposed to a total of 11 antibiotics and displayed resistance towards Ampicillin (10?g), Penicillin-G (10?g) and Trimethoprim (5?g). The isolated organisms were also screened for antibiotic resistant genes (ARGs) using endpoint PCR. Additionally, the Aeromonas isolates (4) were screened to determine the presence of 10 virulence genes. Of the five ARGs screened, 50 % isolates harboured ampC and blaTEm. Whilst none of the screened Aeromonas species harboured any of the screened virulence genes. The physico-chemical quality of the groundwater systems of interest clearly illustrated that the parameters were favourable for bacterial growth. Whilst the presence of pathogenic multi-drug resistant organisms such as Clostridium, Aeromonas, Bacillus and Escherichia sp. harbouring ARBs is a cause for concern. Thus, the findings of this study indicate that groundwater systems in the NWP are a potential safety hazard and require special attention If the water is to be used for consumption.