Franco, Giulio (2009) Most Probable Number and Real-Time PCR Methodology for Simultaneous Detection and Evaluation of Salmonella Strains and Escherichia coli O157:H7 Presence in Irrigation Reservoirs. [Laurea specialistica biennale]
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In general, contamination of food by pathogens of animal origin is well established, but awareness is growing that fresh or minimally processed fruit and vegetables can also be sources of pathogenic bacteria. In particular Escherichia coli O157:H7 and Salmonella spp are known to be emerging human pathogens and are strongly associated with produce-related outbreaks. To better understand whether surface irrigation waters might be a source of these two pathogens, five irrigation ponds were studied. Water microbiological, environmental and chemical factors were studied to determine if there was a correlation between any of these factors and the presence of pathogens. The methodology for pathogens detection combined a Most Probable Number (MPN) method, a filtration technique for large volumes of surface water, a standard selective media and a real-time PCR TaqMan assay. E. coli O157:H7 concentrations ranged from not detectable to 0.98 MPN per L and from below detection limit to 2.07 MPN per L for Salmonella spp. With variables at disposal, it was found that E. coli presence seems to be related with water temperatures whereas Salmonella with nutrients in the water. We were able to explain about 65% of experiment variability of this system indicating there might be others variables governing the occurrence of the pathogens. In these systems more in depth study and more frequent sampling plan can be developed and correlated with the best agricultural and environmental management practices.
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