Browsing by Author "Dobrowsky, Penelope Heather"

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    Comparative analysis of solar pasteurization versus solar disinfection for the treatment of harvested rainwater
    (BioMed Central, 2016-12-09) Strauss, Andre; Dobrowsky, Penelope Heather; Ndlovu, Thando; Reyneke, Brandon; Khan, Wesaal
    Background: Numerous pathogens and opportunistic pathogens have been detected in harvested rainwater. Developing countries, in particular, require time- and cost-effective treatment strategies to improve the quality of this water source. The primary aim of the current study was thus to compare solar pasteurization (SOPAS; 70 to 79 °C; 80 to 89 °C; and ≥90 °C) to solar disinfection (SODIS; 6 and 8 hrs) for their efficiency in reducing the level of microbial contamination in harvested rainwater. The chemical quality (anions and cations) of the SOPAS and SODIS treated and untreated rainwater samples were also monitored. Results: While the anion concentrations in all the samples were within drinking water guidelines, the concentrations of lead (Pb) and nickel (Ni) exceeded the guidelines in all the SOPAS samples. Additionally, the iron (Fe) concentrations in both the SODIS 6 and 8 hr samples were above the drinking water guidelines. A >99% reduction in Escherichia coli and heterotrophic bacteria counts was then obtained in the SOPAS and SODIS samples. Ethidium monoazide bromide quantitative polymerase chain reaction (EMA-qPCR) analysis revealed a 94.70% reduction in viable Legionella copy numbers in the SOPAS samples, while SODIS after 6 and 8 hrs yielded a 50.60% and 75.22% decrease, respectively. Similarly, a 99.61% reduction in viable Pseudomonas copy numbers was observed after SOPAS treatment, while SODIS after 6 and 8 hrs yielded a 47.27% and 58.31% decrease, respectively. Conclusion: While both the SOPAS and SODIS systems reduced the indicator counts to below the detection limit, EMA-qPCR analysis indicated that SOPAS treatment yielded a 2- and 3-log reduction in viable Legionella and Pseudomonas copy numbers, respectively. Additionally, SODIS after 8 hrs yielded a 2-log and 1-log reduction in Legionella and Pseudomonas copy numbers, respectively and could be considered as an alternative, cost-effective treatment method for harvested rainwater.
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    Legionella species persistence mechanisms in treated harvested rainwater
    (Stellenbosch : Stellenbosch University, 2017-03) Dobrowsky, Penelope Heather; Khan, Wesaal; Khan, Sehaam; Cloete, Thomas Eugene; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: The persistence of Legionella spp. at high pasteurization temperatures poses a threat to human health as a number of Legionella spp. are known to cause Legionnaires’ disease. Research has then indicated that the primary factors that allow Legionella to proliferate and persist in water distribution systems are: the accessibility to nutrients in a water source, water temperature, the presence of free-living amoebae (FLA) and other aquatic bacteria. The focus of the current study was thus to investigate and functionalise selected persistence mechanisms displayed by Legionella spp. that aid in their survival in pasteurized and unpasteurized harvested rainwater. The overall aim of Chapter two was to isolate and identify the dominant Legionella spp. persisting in a domestic rainwater harvesting tank and a solar pasteurization (SOPAS) system and to identify possible FLA vectors of Legionella that remain viable at high pasteurization temperatures (>60°C). For this, pasteurized and unpasteurized tank water samples were screened for the dominant Legionella spp. using culture based techniques. In addition, as FLAs including Acanthamoeba spp., Naegleria fowleri and Vermamoeba (Hartmannella) vermiformis are the most frequently isolated from hot water systems, ethidium monoazide polymerase chain reaction (EMA-qPCR) was utilised for the quantification of viable Legionella spp., Acanthamoeba spp., V. vermiformis and N. fowleri. Eighty-two Legionella spp. were isolated from the unpasteurized tank water samples, where L. longbeachae (35 %) was the most frequently isolated, followed by L. norrlandica (27 %) and L. rowbothamii (4 %). This information provides pertinent knowledge on the occurrence and dominant species of Legionella present in the South African environment. In addition, the SOPAS system was effective in reducing the gene copies of viable N. fowleri (5-log) and V. vermiformis (3-log) to below the lower limit of detection at temperatures of 68–93°C and 74–93°C, respectively. In contrast, as gene copies of viable Legionella and Acanthamoeba were still detected after pasteurization at 68–93°C, it could be concluded that Acanthamoeba spp. primarily act as vectors for Legionella spp. in solar pasteurized rainwater. The primary objective of Chapter three was to determine the resistance of three Legionella species isolated from unpasteurized rainwater [L. longbeachae (env.), L. norrlandica (env.) and L. rowbothamii (env.)], two Legionella reference strains (L. pneumophila ATCC 33152 and L. longbeachae ATCC 33462) and Acanthamoeba mauritaniensis ATCC 50676 to heat treatment (50–90°C). In addition, the resistance of L. pneumophila ATCC 33152 and L. longbeachae (env.) in co-culture with A. mauritaniensis ATCC 50676, respectively, to heat treatment (50–90°C) was determined using EMA-qPCR. The interaction mechanisms exhibited between Legionella and Acanthamoeba during heat treatment (50–90°C) were also elucidated by monitoring the relative expression of genes associated with metabolism and virulence of L. pneumophila ATCC 33152 (lolA, sidF, csrA) and L. longbeachae (env.) (lolA) in co-culture with A. mauritaniensis ATCC 50676, respectively. Legionella longbeachae (env.) and L. pneumophila ATCC 33152 were the most resistant to heat treatment as both organisms were still culturable (CFU/mL) following treatment at 50 and 60°C. However, the sensitivity of detection of viable cells was increased when using EMA-qPCR as all Legionella spp. and A. mauritaniensis ATCC 50676 were detected following heat treatment (50–90°C). In addition, while the heat resistance of L. pneumophila ATCC 33152 in co-culture with A. mauritaniensis ATCC 50676 improved, it is postulated that L. longbeachae (env.) is unable to replicate in A. mauritaniensis ATCC 50676 as L. longbeachae (env.) in co-culture was not detected following heat treatment at 80°C and 90°C. Results also showed a clear trend between genes with related function and differential expression during heat treatment (50-90°C). For example, relative to the untreated samples, the expression of lolA remained constant while the expression of sidF increased and the expression of csrA decreased significantly during L. pneumophila ATCC 33152 co-culture with A. mauritaniensis ATCC 50676. Results thus confirm that while heat treatment may reduce the number of viable Legionella spp., L. pneumophila is able to interact with A. mauritaniensis and persist during heat treatment. The overall aim of Chapter four was to elucidate other microbial and physico-chemical characteristics that may be associated with the incidence of Legionella spp. and Acanthamoeba spp. in rainwater harvested from different roofing materials. Overall results indicated that the roofing materials did not influence the incidence of Legionella and Acanthamoeba spp. as these organisms were detected in all tank water samples collected from the Chromadek®, galvanized zinc and asbestos roofing materials. However, significant (p < 0.05) positive Spearman (ρ) correlations were noted between Legionella spp. vs. nitrites and nitrates and between Acanthamoeba spp. vs. barium, magnesium, sodium, silicon, arsenic and phosphate, respectively. In addition, while no significant correlations were observed between Legionella spp. vs. the indicator bacteria (p > 0.05), positive correlations were established between Acanthamoeba spp. vs. total coliforms and Escherichia coli, respectively. Results thus indicated that the incidence of Legionella and Acanthamoeba spp. in harvested rainwater may primarily be due to external pollutants such as dust and animal faecal matter present on the catchment system.
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    Quality assessment of domestic harvested rainwater in the peri-urban region of Kleinmond, Western Cape and the optimisation of point-of-use treatment systems
    (Stellenbosch : Stellenbosch University, 2014-04) Dobrowsky, Penelope Heather; Khan, Wesaal; Cloete, Eugene; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: Domestic rainwater harvesting (DRWH) refers to the collection and storage of rainwater for domestic purposes and in an effort to achieve the Millennium Development Goals (MGD), the South African government has started an initiative where DRWH tanks are financed in sustainable housing schemes in an aim to provide an additional water source directly to households. Although many provinces, including parts of the Eastern Cape and KwaZulu Natal, have been using harvested rainwater as a potable water source, there are a limited number of studies indicating the quality of harvested rainwater in South Africa. However, many studies, internationally, have indicated that while the practice of harvesting rainwater is gaining popularity, rainwater quality is not within potable standards (Chapter 1). During the first phase of the study, rainwater samples were collected from the Kleinmond Housing Scheme (Western Cape, South Africa). From a cluster of 411 houses, the DRWH tanks connected to 29 houses were selected for monitoring the microbial and physico-chemical properties of harvested rainwater. Drinking water guidelines stipulated by SANS 241 (2005), DWAF (1996), ADWG (NHMRC and NRMMC, 2011) and WHO (2011) were used throughout the study to monitor the quality of rainwater. Eight sampling sessions were then conducted from March to August 2012, during a high and low rainfall period. Overall, the physico-chemical parameters of the rainwater samples were within the respective drinking water guidelines. However, the microbiological analysis verified results obtained in international studies, and showed that the indicator bacteria numbers present in the DRWH samples exceeded the stipulated guidelines (Chapter 2 and 3). Species specific primers were also used to routinely screen for the virulent genes, aggR, stx, eae and ipaH found in Enteroaggregative E. coli (EAEC), Enterohaemorrhagic E. coli (EHEC), Enteropathogenic E. coli (EPEC) and Enteroinvasive E. coli (EIEC), respectively, in the rainwater samples. The virulent pathogenic E. coli genes were then detected in 3% (EPEC and EHEC) and 16% (EAEC) of the 80 rainwater samples collected routinely during the sampling period from ten DRWH tanks (Chapter 3). Bacterial isolates selected during the high rainfall period (June to August 2012), as well as PCR assays performed on total genomic DNA extraction from the rainwater samples, confirmed the presence of numerous pathogenic bacteria including Legionella spp. Klebsiella spp. and Shigella spp. Yersinia spp. were also isolated and detected for the first time in DRWH tanks (Chapter 4). Based on the results obtained in the first phase and as many studies have indicated the poor quality of rainwater, the second phase of the project was aimed at designing and monitoring point of use treatment systems. Three polyethylene DRWH tanks (2000 L) were installed at the Welgevallen Experimental farm, Stellenbosch University, South Africa. Various treatment systems, such as activated carbon and slow sand filtration, solar pasteurization and a combined activated carbon/PVA nanofibre filtration column, were then intermittently connected to the three DRWH tanks during the high rainfall period (June to October 2013). Results for slow sand filtration and activated carbon filters indicated that the biological layer that had developed on the filtration media had not matured and for this reason chemical and microbial parameters were not reduced to within drinking water guidelines. A polyvinyl (alcohol) (PVA) nanofibre membrane without activated carbon in a column filtration system was analysed and results indicated that this system was also not effective in reducing the microbial numbers to within drinking water guidelines. Lastly, by utilising a PVA nanofibre membrane with activated carbon in a column filtration system, one litre of potable water was produced and all heterotrophic bacteria, E. coli and total coliform counts were reduced to zero and were within drinking water guidelines (Chapter 5). For the solar pasteurization system (Chapter 6), at treatment temperatures of greater than 72°C, all heterotrophic bacteria, E. coli and total coliforms were reduced to zero and were within drinking water guidelines. However, PCR assays confirmed the presence of Yersinia spp., Legionella spp., and Pseudomonas spp., at temperatures greater than 72°C. Results for chemical analysis also indicated all cations were within the international and national drinking water guidelines, with the exception of iron, aluminium, lead and nickel, which were detected in the pasteurized rainwater samples and were above the respective guidelines. It is hypothesised that these elements could have leached from the stainless steel storage tanks of the pasteurization system and it is therefore recommended that the storage tank of the pasteurization system be manufactured from an alternative material, such as a high grade polymeric material, which is able to withstand the high temperatures yet will not negatively influence the quality of harvested rainwater.