Maggy Ndombo Benteke Momba

Impact of seasonal variation on Escherichia coli concentrations in the riverbed sediments in the Apies River, South Africa.

Many South Africans living in resource-poor settings with little or no access to pipe-borne water still rely on rivers as alternative water sources for drinking and other purposes. The poor microbial quality of such water bodies calls for appropriate monitoring. However, routine monitoring only takes into consideration the microbial quality of the water column, and does not include monitoring of the riverbed sediments for microbial pollution. This study sought to investigate the microbial quality of riverbed sediments in the Apies River, Gauteng Province, South Africa, using Escherichia coli as a faecal indicator organism and to investigate the impact of seasonal variation on its abundance. Weekly samples were collected at 10 sampling sites on the Apies River between May and August 2013 (dry season) and between January and February 2014 (wet season). E. coli was enumerated using the Colilert®-18 Quanti-Tray® 2000 system. All sites tested positive for E. coli. Wastewater treatment work effluents had the highest negative impact on the river water quality. Seasonal variations had an impact on the concentration of E. coli both in water and sediments with concentrations increasing during the wet season. A strong positive correlation was observed between temperature and the E. coli concentrations. We therefore conclude that the sediments of the Apies River are heavily polluted with faecal indicator bacteria and could also harbour other microorganisms including pathogens. The release of such pathogens into the water column as a result of the resuspension of sediments due to extreme events like floods or human activities could increase the health risk of the populations using the untreated river water for recreation and other household purposes. There is therefore an urgent need to reconsider and review the current South African guidelines for water quality monitoring to include sediments, so as to protect human health and other aquatic lives.

Comparing the tolerance limits of selected bacterial and protozoan species to nickel in wastewater systems.

Heavy-metal resistant microorganisms play a significant role in the treatment of industrial wastewater. The detoxifying ability of these resistant microorganisms can be manipulated for bioremediation of heavy metals in wastewater systems. This study aimed at comparing the tolerance limit of selected wastewater protozoan species (Aspidisca sp., Trachelophyllum sp. and Peranema sp.) against Ni(2+) with that of selected bacterial species (Bacillus licheniformis-ATCC12759, Brevibacillus laterosporus-ATCC64 and Pseudomonas putida-ATCC31483) commonly found in wastewater systems. The isolates were exposed to various concentrations of Ni(2+) in mixed liquor and their tolerance to Ni(2+) assessed at different temperatures (25°C, 30°C, 35°C and 40°C) and pHs (4, 6, 7, 8 and 10). The physicochemical parameters such as chemical oxygen demand (COD) and dissolved oxygen (DO) of the media and the growth rates of the isolates were measured using standard methods. In terms of their minimum inhibitory concentrations (MIC), the results revealed that the isolates could tolerate Ni(2+) at concentrations ranging between 32 and 52ppm for protozoa and between 52 and 84ppm for bacteria. B. licheniformis-ATCC12759 was the most tolerant bacterial species (MIC: 84ppm-Ni(2+)) while Peranema sp. was the most tolerant protozoan species (MIC: 52ppm-Ni(2+)). At 10 and/or 20ppm-Ni(2+) the growth of B. licheniformis-ATCC12759 (6.30 days(-1) for 10 and 5.73 days(-1) for 20ppm-Ni(2+)), P. putida-ATCC31483 (6.02 days(-1) for 10 and 5.31 days(-1) for 20ppm-Ni(2+)) and Peranema sp. (2.15 days(-1) for 10ppm-Ni(2+)) was stimulated after one day of incubation. Statistical evidence showed significant differences (p=0.0065) between the MIC of the six isolates and positive correlations between COD and the growth rates of isolates (r=0.8999/0.8810 for bacteria/protozoa). The tolerance limit of all isolates was significantly dependent on the pH and the temperature. The study suggests that these isolates can be used for the bioremediation of nickel in industrial wastewater systems.

Prevalence of enteropathogenic bacteria in treated effluents and receiving water bodies and their potential health risks

The failure of wastewater treatment plants to produce effluents of a high microbiological quality is a matter of great concern in terms of water resource pollution. A more serious concern is that this water source is used by communities in developing countries for multiple purposes, which include drinking, recreation and agriculture. The current study investigated the prevalence and potential health risks of enteropathogenic bacteria (Salmonella typhimurium, Shigella dysenteriae and Vibrio cholerae) in the treated effluents of three selected South African Wastewater Treatment Works as well as their receiving water bodies. Culture-based and polymerase chain reaction techniques were used to detect and identify the pathogenic bacteria. The conventional methods revealed that of the 272 water samples collected, 236 samples (86.8%) tested presumptively positive for Salmonella spp., 220 samples (80.9%) for Shigella spp. and 253 samples (93.0%) for V. cholerae. Molecular test results indicated that out of the randomly selected presumptive positive samples (145), zero to 60% of samples were positive for S. typhimurium and S. dysenteriae and 20% to 60% for V. cholerae. For the health risk assessment, the daily combined risk of S. typhimurium, S. dysenteriae and V. cholerae infection was above the lowest acceptable risk limit of 10(-4) as estimated by the World Health Organization for drinking water. This study showed that the target treated wastewater effluents and their receiving water bodies could pose a potential health risk to the surrounding communities.

Riverbed sediments in the Apies River, South Africa: recommending the use of both Clostridium perfringens and Escherichia coli as indicators of faecal pollution

PurposeSediments have been shown to contribute to the microbial quality of the water column during resuspension and serve as reservoirs for potentially pathogenic organisms. Currently, definitive guidelines regarding microbial indicators that need to be assessed in order to monitor faecal pollution in sediments do not exist. In this study, Escherichia coli (a well-established indicator) and Clostridium perfringens were monitored to determine their suitability as indicators for faecal pollution of sediments.Materials and methodsEnumeration of E. coli in water was performed using the ColilertTM 18/Quantitray-2000 system from IDEXX. Identification and enumeration of C. perfringens in water was conducted using the boil method followed by the pour plate technique. Real-time polymerase chain reaction (RT-PCR) was used to confirm isolates. E. coli and C. perfringens were enumerated in sediment by firstly using the water displacement approach to dislodge organisms from sediment and then subsequently followed by the same methods as those used for detection and enumeration of the two potential indicators in water.Results and discussionThe highest concentrations of E. coli and C. perfringens were obtained along the main stem of the Apies River which was characterised by the presence of wastewater treatment works, animal farmlands and informal settlements with inadequate sanitary facilities. The lowest concentration of both organisms was observed along the tributaries of the river, where there was minimal faecal pollution-related activity. Due to the difference in biological characteristics and survival patterns, concentrations of E. coli in sediments fluctuated (higher concentrations in the wet season) during the entire sampling period while concentrations of C. perfringens remained stable. There was a positive correlation between temperature and the presence of both organisms in the sediment, indicating the enabling environment of sediment to aid in bacterial survival.ConclusionsE. coli and C. perfringens are both suitable indicators of faecal pollution in riverbed sediments. However, both organisms need to be monitored together for accurate assessment of the faecal pollution of sediments. E. coli remains a good indicator of recent faecal pollution and provides insight into the short-term impact of faecal pollution, while C. perfringens gives an indication of the long-term impact of faecal deposition in riverbed sediments due to the organisms’ persistence in the environment.

Quantitative microbial risk assessment (QMRA) shows increased public health risk associated with exposure to river water under conditions of riverbed sediment resuspension.

Although higher microbial concentrations have been reported in sediments than in the overlying water column, most quantitative microbial risk assessment (QMRA) studies have not clearly indicated the contribution of sediment-borne pathogens to estimated risks. Thus, the present study aimed at determining the public health risk associated with exposure to pathogenic bacteria in polluted river water under undisturbed conditions and conditions of sediment resuspension in the Apies River, Gauteng, South Africa. Microbial pathogens were isolated and identified using culture and molecular methods. The beta-Poisson dose-response model was used to estimate the probability of infection (Pi) with the various pathogens, following accidental/intentional ingestion of 1mL or 100mL (or 50mL) of untreated river water. Mean wet season Escherichia coli counts ranged between 5.8E+01 and 8.8E+04MPN/100mL (water column) and between 2.40E+03 and 1.28E+05MPN/100mL (sediments). Mean dry season E. coli counts ranged between 5.11E+00 and 3.40E+03MPN/100mL (water column) and between 5.09E+00 and 6.30E+03MPN/100mL (sediments). Overall (water and sediments) Vibrio cholerae was the most detected pathogen (58.8%) followed by Salmonella spp. (23.9%) and Shigella (10.1%). Ingestion of 1mL of river water could lead to 0%-4% and 1%-74% Pi with E. coli during the dry and wet season, respectively. During the dry season, the Pi with V. cholerae, Salmonella spp. and Shigella spp. were 0%-1.39%, 0%-4.11% and 0%-0.16% respectively, depending on volume of water ingested. The risks of infections with all microorganisms increased during the wet season. A 2-log increase in water E. coli count following sediments disturbance led to approximately 10 times higher Pi with E. coli than when sediments were undisturbed. Therefore, the use of the untreated water from the Apies River for drinking, household purposes or recreational activities poses a potential health risk to the users of the river.

Microbial Remobilisation on Riverbed Sediment Disturbance in Experimental Flumes and a Human-Impacted River: Implication for Water Resource Management and Public Health in Developing Sub-Saharan African Countries

Resuspension of sediment-borne microorganisms (including pathogens) into the water column could increase the health risk for those using river water for different purposes. In the present work, we (1) investigated the effect of sediment disturbance on microbial resuspension from riverbed sediments in laboratory flow-chambers and in the Apies River, Gauteng, South Africa; and (2) estimated flow conditions for sediment-borne microorganism entrainment/resuspension in the river. For mechanical disturbance, the top 2 cm of the sediment in flow-chambers was manually stirred. Simulating sudden discharge into the river, water (3 L) was poured within 30 s into the chambers at a 45° angle to the chamber width. In the field, sediment was disturbed by raking the riverbed and by cows crossing in the river. Water samples before and after sediment disturbance were analysed for Escherichia coli. Sediment disturbance caused an increase in water E. coli counts by up to 7.9–35.8 times original values. Using Shields criterion, river-flow of 0.15–0.69 m3/s could cause bed particle entrainment; while ~1.57–7.23 m3/s would cause resuspension. Thus, sediment disturbance in the Apies River would resuspend E. coli (and pathogens), with possible negative health implications for communities using such water. Therefore, monitoring surface water bodies should include microbial sediment quality.

Riverbed Sediments as Reservoirs of Multiple Vibrio cholerae Virulence-Associated Genes: A Potential Trigger for Cholera Outbreaks in Developing Countries

Africa remains the most cholera stricken continent in the world as many people lacking access to safe drinking water rely mostly on polluted rivers as their main water sources. However, studies in these countries investigating the presence of Vibrio cholerae in aquatic environments have paid little attention to bed sediments. Also, information on the presence of virulence-associated genes (VAGs) in environmental ctx-negative V. cholerae strains in this region is lacking. Thus, we investigated the presence of V. cholerae VAGs in water and riverbed sediment of the Apies River, South Africa. Altogether, 120 samples (60 water and 60 sediment samples) collected from ten sites on the river (January and February 2014) were analysed using PCR. Of the 120 samples, 37 sediment and 31 water samples were positive for at least one of the genes investigated. The haemolysin gene (hlyA) was the most isolated gene. The cholera toxin (ctxAB) and non-O1 heat-stable (stn/sto) genes were not detected. Genes were frequently detected at sites influenced by human activities. Thus, identification of V. cholerae VAGs in sediments suggests the possible presence of V. cholerae and identifies sediments of the Apies River as a reservoir for potentially pathogenic V. cholerae with possible public health implications.

Comparing the effectiveness of five low-cost home water treatment devices for Cryptosporidium, Giardia and somatic coliphages removal from water sources

AbstractThis study compared the effectiveness and sustainability of five selected cost-effective home water treatment systems in removing Cryptosporidium and Giardia spp. from water sources. These systems included: silver impregnated porous pot (SIPP), biosand filter combined with zeolite (BSF-Z), biosand filter without zeolite (BSF-S), bucket filter (BF) and ceramic candle filter (CCF). The USEPA Methods 1623 were used for the isolation and the detection of the protozoan parasites. The flow rates of the devices ranged between 0.05 and 160.5 L/h. The average turbidity of the environmental intake water samples ranged between 1.47 and 42.93 NTU before filtration and between 0.05 and 14.49 NTU after filtration. The performance of the SIPP in removing the parasites (98–100% of both oocysts and cysts from synthetic water; 96–99.6% oocysts and 96.6–99.8% cysts from the environmental water sources) and in removing viral indicator (97.7–100%) was found to be significantly higher (p < 0.05) compared to other filte...