Research Institutes
Permanent URI for this communityhttp://ir-dev.dut.ac.za/handle/10321/840
Browse
6 results
Search Results
Item A theoretical approach to using faecal indicator data to model norovirus concentration in surface water for QMRA : Glomma River, Norway(Elsevier, 2016) Petterson, Susan R.; Stenström, Thor-Axel; Ottoson, JakobMonitoring of faecal indicator organisms, such as Escherichia coli, in environmental and drinking waters is inadequate for the protection public health, primarily due to the poor relationship between E. coli and the occurrence of human pathogens, especially viruses, in environmental samples. Nevertheless, measurements of faecal indicator organisms within the risk based approach, can provide valuable information related to the magnitude and variability of faecal contamination, and hence provide insight into the expected level of potential pathogen contamination. In this study, a modelling approach is presented that estimates the concentration of norovirus in surface water relying on indicator monitoring data, combined with specific assumptions regarding the source of faecal contamination. The model is applied to a case study on drinking water treatment intake from the Glomma River in Norway. Norovirus concentrations were estimated in two sewage sources discharging into the river upstream of the drinking water offtake, and at the source water intake itself. The characteristics of the assumed source of faecal contamination, including the norovirus prevalence in the community, the size of the contributing population and the relative treatment efficacy for indicators and pathogens in the sewage treatment plant, influenced the magnitude and variability in the estimated norovirus concentration in surface waters. The modelling exercise presented is not intended to replace pathogen enumeration from environmental samples, but rather is proposed as a complement to better understand the sources and drivers of viruses in surface waters. The approach has the potential to inform sampling regimes by identifying when the best time would be to collect environmental samples; fill in the gaps between sparse datasets; and potentially extrapolate existing datasets in order to model rarer events such as an outbreak in the contributing population. In addition, and perhaps most universally, in the absence of pathogen data, this approach can be used as a first step to predict the source water pathogen concentration under different contamination scenarios for the purpose of quantifying microbial risks.Item Effect of interaction of methanol leaf extract of Spondias Mombin (Linn) and Amoxicillin on some Diarrheagenic Escherichia coli(Pharmacotherapy Group, 2016-03) Adegoke, Anthony Ayodeji; Aiyegoro, Olayinka A.; Stenström, Thor-AxelPurpose: To study the effect of interaction between methanol leaf extract of Spondias mombin and amoxicillin on diarrheagenic Escherichia coli (DEC). Methods: Cold methanol extraction of Spondias mombin leaf and its phytochemical screening were carried out. Isolated, characterized and identified strains of enterotoxigenic E. coli (ETEC), enteroinvasive E. coli (EIEC), and enterohemorrhagic E. coli (EHEC) from watery stool, mucoid bloody stool and watery bloody stool of diarrheal patients, respectively, were confirmed and typed by conventional and molecular methods. The minimum inhibitory concentration (MIC) and ½ MIC at which the extract and amoxicillin interacted were determined. Results: Spondias mombin extract showed remarkable antibacterial activity at extract concentration of 50 - 200 mg/mL with a mean zone of inhibition (MZ) ≥ 11.1 and activity index (AI) of 0.8 - 1.1. MIC of 12.5 mg/mL was observed for both ETEC and EIEC while it was 6.25 mg/mL for EHEC. The extract showed synergistic interaction at various concentrations (50 – 200, 12.5 and 6.25 mg/mL, respectively) with amoxycillin against ETEC, EHEC and EIEC. Synergy across a wide range of concentrations compared favourably with the ½ MIC and MIC of both extract and amoxycillin for ETEC. The extract contained moderate levels of alkaloids, flavonoids and tannins, as well as a lot of saponins, and low levels of phenol. The activity of the extract of Spondias mombin compares well with that of amoxicillin with AI ≥ 1 in some cases. Conclusion: A synergistic interaction between the leaf extract of S. mombin and amoxicillin confirms the extract as potential antibacterial agent but further studies are required to ascertain this.Item Evaluation of operating conditions for sustainable harvesting of microalgal biomass applying electrochemical method using non sacrificial electrodes(Elsevier, 2015) Misra, Rohit; Guldhe, Abhishek; Singh, Poonam; Rawat, Ismail; Stenström, Thor-Axel; Bux, FaizalThe efficient harvesting of microalgae is considered to be one of the challenging steps of algal biofuel production and a key factor limiting the commercial use of microalgae. To overcome the limitation of metallic electrodes depletion, the application of non-sacrificial electrode was investigated for the electrochemical harvesting (ECH) of microalgae. The effect of applied current, addition of electrolyte and initial pH were parameters investigated. The highest recovery efficiency of 83% was obtained for Scenedesmus obliquus at 1.5 A, initial pH 9 and 6 g L−1 NaCl with power consumption of 3.84 kWh kg−1. Recovery efficiency of ECH process was comparable to literature reported centrifugation, filtration and chemical flocculation techniques but with a much lower power consumption. The ECH process with addition of electrolyte enhanced the lipid extraction by 22% without any adverse effects. The ECH process with non sacrificial carbon electrodes could be a possible harvesting step at commercial scale microalgal biomass production.Item Evaluation of phytotoxicity effect on selected crops using treated and untreated wastewater from different configurative domestic wastewater plants(Taylor and francis Online, 2016) Ravindran, B.; Kumari, Sheena K.; Stenström, Thor-Axel; Bux, FaizalThis study investigated the phytotoxicity effect of untreated and treated wastewater collected from two different configurations of domestic wastewater treatment plants in South Africa. The phytotoxicity effect on vegetable seed growth was studied in terms of germination index (GI), relative seed germination (RSG) and relative root elongation (RRE) using four commercial crop varieties, viz., tomato (Lycopersicon esculentum), radish (Raphanus sativus), carrot (Daucus carota) and onion (Allium cepa). According to phyototoxicity limits, 80% germination and above is regarded as non-toxic and less than 50% GI is regarded as highly toxic and not suitable for agricultural purposes. In our study, seeds were irrigated with concentrations of 25%, 50%, 75%, 100% of treated effluent (TE) and untreated effluent (UTE). The TE results were best with the highest GI (%) recorded as tomato, 177; carrot, 158.5; onion, 132; and lettuce, 124. The results of this study indicate that TE showed no phytotoxicty effects and recorded above 80% GI. The UTE irrigated crops reached a GI of only 50% and above which is clear evidence of the beneficial effect of waste water treatment. The overall results confirmed that treated wastewater has a beneficial effect on agricultural crops and can be used as a liquid fertilizer.Item A probabilistic assessment of the contribution of wastewater-irrigated lettuce to Escherichia coli O157:H7 infection risk and disease burden in Kumasi, Ghana(IWA Publishing, 2015-03) Seidu, Razak; Abubakari, Amina; Amoah, Isaac Dennis; Heistad, Arve; Stenström, Thor-Axel; Larbi, John A.; Abaidoo, Robert ClementWastewater use for vegetable production is widespread across the cities of many developing countries. Studies on the microbial health risks associated with the practice have largely depended on faecal indicator organisms with potential underestimation or overestimation of the microbial health risks and disease burdens. This study assessed the Escherichia coli O157:H7 infection risk and diarrhoeal disease burden measured in disability-adjusted life years (DALYs) associated with the consumption of wastewater-irrigated lettuce in Kumasi, Ghana using data on E. coli O157:H7 in ready-to-harvest, wastewater-irrigated lettuce. Two exposure scenarios – best case and worst case – associated with a single consumption of wastewater-irrigated lettuce were assessed. The assessment revealed wastewater-irrigated lettuce is contributing to the transmission of E. coli O157:H7 in Kumasi, Ghana. The mean E. coli O157:H7 infection risk and DALYs in the wet and dry seasons, irrespective of the exposure scenario, were above the World Health Organization tolerable daily infection risk of 2.7 × 10−7 per person per day and 10−6 DALYs per person per year. It is recommended that legislation with clear monitoring indicators and penalties is implemented to ensure that farmers and food sellers fully implement risk mitigating measures.Item Comparative assessment of the bacterial communities associated with Aedes aegypti larvae and water from domestic water storage containers(Parasites and Vectors, 2014) Dada, Nsa; Jumas-Bilak, Estelle; Manguin, Sylvie; Seidu, Razak; Stenström, Thor-Axel; Overgaard, Hans J.Background: Domestic water storage containers constitute major Aedes aegypti breeding sites. We present for the first time a comparative analysis of the bacterial communities associated with Ae. aegypti larvae and water from domestic water containers. Methods: The 16S rRNA-temporal temperature gradient gel electrophoresis (TTGE) was used to identify and compare bacterial communities in fourth-instar Ae. aegypti larvae and water from larvae positive and negative domestic containers in a rural village in northeastern Thailand. Water samples were cultured for enteric bacteria in addition to TTGE. Sequences obtained from TTGE and bacterial cultures were clustered into operational taxonomic units (OTUs) for analyses. Results: Significantly lower OTU abundance was found in fourth-instar Ae. aegypti larvae compared to mosquito positive water samples. There was no significant difference in OTU abundance between larvae and mosquito negative water samples or between mosquito positive and negative water samples. Larval samples had significantly different OTU diversity compared to mosquito positive and negative water samples, with no significant difference between mosquito positive and negative water samples. The TTGE identified 24 bacterial taxa, belonging to the phyla Proteobacteria, Firmicutes, Actinobacteria, Bacteroidetes and TM7 (candidate phylum). Seven of these taxa were identified in larval samples, 16 in mosquito positive and 13 in mosquito negative water samples. Only two taxa, belonging to the phyla Firmicutes and Actinobacteria, were common to both larvae and water samples. Bacilli was the most abundant bacterial class identified from Ae. aegypti larvae, Gammaproteobacteria from mosquito positive water samples, and Flavobacteria from mosquito negative water samples. Enteric bacteria belonging to the class Gammaproteobacteria were sparsely represented in TTGE, but were isolated from both mosquito positive and negative water samples by selective culture. Conclusions: Few bacteria from water samples were identified in fourth-instar Ae. aegypti larvae, suggesting that established larval bacteria, most likely acquired at earlier stages of development, control the larval microbiota. Further studies at all larval stages are needed to fully understand the dynamics involved. Isolation of enteric bacteria from water samples supports earlier outcomes of E. coli contamination in Ae. aegypti infested domestic containers, suggesting the need to further explore the role of enteric bacteria in Ae. aegypti infestation.