Bacterial pathogen presence and survival in water and manure addressing pre-harvest produce safety
Date
2019
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Abstract
Understanding the different reservoirs of pathogens and the means by which pathogens come in contact with fresh produce in the farm environment is key to reducing the number of illnesses. The purpose of this thesis is to gain a better understanding of the survival and infectivity of Listeria monocytogenes in surface water potentially used for irrigation. and the presence and prevalence of Salmonella enterica spp. and shiga toxigenic Escherichia coli (STEC) in poultry litter and cattle manure, respectively used as untreated fertilizer. ☐ In one study, tidal brackish river surface water samples were collected from June to September 2018 and, along with a 1% Buffered Peptone Water (BPW) control, inoculated with L. monocytogenes isolates and incubated at 16 °C. On days 0, 3, 5, 7, and 10 culturable L. monocytogenes were enumerated on Brilliance Listeria Agar (BLA). In addition, on days 0, 7, and 10, the ability of L. monocytogenes in the samples to infect HCT-8 cells was determined. In another study, manure samples were collected during 42 and 23 visits to 22 poultry and 13 cattle farms, respectively. A most probable number (MPN) assay was used to quantify the presence of STEC and Salmonella enterica. Colonies from potential positive samples were confirmed via PCR using stx1, stx2, eae, and invA primers. ☐ L. monocytogenes isolates survived and remained infectious over the 10-day incubation period but in surface water their numbers declined whereas their numbers in 1% BPW remained consistent. ☐ Salmonella and STEC were detected in litter and manure from different farms in the Mid-Atlantic at a rate between 41% (121/294) and 19% (30/161) respectively but varied by season collected. Poultry farms managed as organic had higher rates of Salmonella than farms managed as conventional. Positive poultry litter samples had higher moisture contents than negative samples and Tetrathionate Broth's MPN values were higher than those determined by Rappaport Vassiliadis Broth. ☐ In summary, L. monocytogenes can survive and remain infectious in surface water potentially used for crop irrigation and the presence of STEC and Salmonella in litter and manure is of concern as these pathogens can be transferred to produce when land applied.
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Keywords
Irrigation water, Listeria monocytogenes, Manure, Pre-harvest produce safety, Salmonella enterica, Shiga toxigenic Escherichia coli