Browsing by Author "Nocker, A."
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Item Open Access Disruption of cells in biosolids affects E. coli dynamics in storage(IWA Publishing, 2019-05-22) Fane, Sarah Elizabeth; Madureira, D.; Nocker, A.; Vale, P.; Rivas Casado, Monica; Wilson, A.; Bajón Fernández, Yadira; Harris, Jim A.; Cartmell, Elise; Tyrrel, SeanAchieving microbial compliance during biosolids storage can be complicated by the unpredictable increase of Escherichia coli. Thermal treatment during anaerobic digestion (AD) and the effects of dewatering may be a significant factor contributing to indicator survival. Shear forces present during dewatering may promote cell damage, releasing nutrient for E. coli growth. The effect of cell damage on E. coli survival was assessed in laboratory-scale thermal and physical disruption experiments. E. coli growth curves for disrupted treatments were compared with control conditions and quantified using flow cytometry and membrane filtration techniques. A significant difference (p < 0.05) in the level of damaged cells between control and disrupted conditions was observed. For thermal and physical disruption treatments, the peak of E. coli concentration increased significantly by 1.8 Log and 2.4 Log (CFU (colony forming units) g−1 DS), respectively, compared with control treatments. Research findings contribute to the understanding of bacterial growth and death dynamics in biosolidsItem Open Access Effect of temperature on bacteriophage-mediated lysis efficiency with a special emphasis on bacterial temperature history(University of Mohammed Premier, Oujda, Morocco, 2022-09-30) Ameh, E. M.; Nocker, A.; Tyrrell, Sean; Harris, Jim A.; Orlova, E. V.; Ignatiou, A.Despite the great potential of phages as biocontrol agents, there is much uncertainty about the environmental factors influencing lysis efficiency. In this study we investigated the effect of temperature using three distinct lytic E. coli phages that were isolated from a single environmental water sample. All three were identified as dsDNA phages belonging to the Myoviridae family. Whereas the optimal growth temperature of E. coli is well known to be 37 ˚C and exposure of phages (prior to mixing with bacteria) to temperatures between 4 and 37˚C did not affect their infectivity, plaque sizes and numbers greatly decreased with increasing incubation temperature (20˚C, 30˚C, 37˚C) of the phage-host mix. At 37˚C, no visible plaques were observed. Results suggest that temperature sensitivity of the phage-host interaction is distinct from the temperature susceptibility of the two players and corroborate previous reports that highest lysis rates are obtained at temperatures approximate with ambient conditions of the phage environment. Infectivity was however found not only to depend on the incubation temperature of the phage-host mix, but also on the bacterial temperature history. Moreover, exposure of bacteria to heat stress prior to phage challenge resulted in a phage-resistant phenotype raising the question whether bacterial pathogens shed from warm-blooded hosts might be less susceptible to phages adapted to environmental temperature conditions.Item Open Access When are bacteria dead? A step towards interpreting flow cytometry profiles after chlorine disinfection and membrane integrity staining(Taylor & Francis: STM, Behavioural Science and Public Health Titles, 2016-12-05) Nocker, A.; Cheswick, R.; Dutheil de la Rochere, P. M.; Denis, M.; Léziart, T.; Jarvis, PeterFlow cytometry is increasingly employed by drinking water providers. Its use with appropriate fluorescent stains allows the distinction between intact and membrane-damaged bacteria, which makes it ideally suited for assessment of disinfection efficiency. In contrast to plate counting, the technology allows the visualization of the gradual loss of membrane integrity. Although this sensitivity per se is very positive, it creates the problem of how this detailed viability information compares with binary plate counts where a colony is either formed or not. Guidelines are therefore needed to facilitate interpretation of flow cytometry results and to determine a degree of membrane damage where bacteria can be considered ‘dead’. In this study we subjected Escherichia coli and environmental microorganisms in real water to increasing chlorine concentrations. Resulting flow cytometric patterns after membrane integrity staining were compared with culturability and in part with redox activity. For laboratory-grown bacteria, culturability was lost at lower disinfectant concentrations than membrane integrity making the latter a conservative viability parameter. No recovery from chlorine was observed for four days. For real water, loss of membrane integrity had to be much more substantial to completely suppress colony formation, probably due to the heterogenic composition of the natural microbial community with different members having different susceptibilities to the disinfectant.