Browsing by Author "Williams, Tyson"
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Item Open Access Competitive exclusion as a means to reduce Escherichia coli regrowth in digested sludge(Cranfield University, 2014-09) Williams, Tyson; Harris, Jim A.; Tyrrel, Sean; Ritz, K.In recent years, it has been reported that numbers of Escherichia coli increase significantly following centrifugation of sludge during the treatment process. E. coli is used as an indicator of the microbiological quality of sludge-derived products destined for agricultural recycling and of the efficacy of the sludge treatment processes. The re-growth phenomenon is of concern because of the potential for additional treatment requirement / higher disposal costs and loss of consumer confidence associated with a compliance failure. It is hypothesised that a competitive exclusion treatment could be the solution wherein the digestate be exposed to a ‘probiotic’ or defined mixture of micro-organisms, to effectively out compete or eliminate any resident E. coli remaining following treatment. The competitive exclusion principle as a treatment method has already seen application in various industrial sectors, the most well-known being the poultry industry. In experiments it was determined that an antimicrobial producing organism would be most likely to succeed. From the candidates screened, Lactobacillus reuteri proved the most promising. L. reuteri is a known producer of reuterin in the presence of glycerol and organic acids as a part of its normal metabolic activity. In sludge derived nutrient broth in the presence of glycerol and low pH, L. reuteri addition resulted in a reduction of E. coli to undetectable levels. In sludge cake under the same conditions, L. reuteri was less successful. However the addition of glycerol and L. reuteri to sludge cake restricted E. coli growth to a 2 log increase from the initial concentration of E. coli recorded following pasteurisation (an average of around 1x102 cfu/gDs), in comparison in the positive control a 4 log increase was recorded. From this result the sludge cake could be defined as conventionally treated. It can be concluded that competitive exclusion and L. reuteri show promise as a treatment for reducing E. coli re-growth in sludge cakeItem Open Access The rapid analysis of fungal growth in the presence of inhibitory effects(Cranfield University, 2011-09) Williams, Tyson; Lambert, R. J. W.For fungal contamination of foodstuffs, there are no fast, reliable, automated techniques to examine growth, nor have any predictive models been developed to describe the growth in the same way as for bacteria. Traditional plating methods can take 3 to 7 days to get adequate results depending on the fungal species utilised and well over a month for challenge testing, an unacceptable delay especially for the food industry. In this study two rapid analysis techniques were investigated, conductimetry (direct and indirect) and turbidimetry (Bioscreen), with the sole objective being to analyse their capability to detect fungal growth in optimum conditions and in the presence of inhibitory agents, in this case sorbic acid and vanillin. Three fungal (Aspergillus niger, Fusarium oxysporum and Pencillium verrucosum and one yeast species (Saccharomyces cerevisiae) were used, though only A. niger growth was analysed using both of the rapid analysis techniques. Two bacterial species (Escherichia coli and Salmonella enterica serovar typhimurium) were also tested using the conductimetry technique for comparison. It was found that both the impedance and turbidimetry methods provided a sensitive and rapid means of detecting, and, under standardised conditions, measuring the activity of micro-organisms. The rate of response showed close correlation with the concentration of both bacteria and spores in the initial inoculum for each strain tested so correlation curves could be constructed to estimate the number of viable cells and spores in a suspension. Moreover, both methods can be used for the accurate screening of potential antimicrobial substances. In comparison with the turbidimetry method though, the impedance method did show a greater deal of variability and there is the possibility it is unsuitable for the analysis of certain fungal species. In addition the direct impedance technique was found to be completely unusable for the analysis of fungal growth. Despite these disadvantages both are promising rapid alternatives to the standard plating technique.