AFAB

Keywords: feces, persistence, Salmonella Dublin, Salmonella Typhimurium, slurry, soil, Verocytotoxigenic E. coli, water

Abstract:

The aim of this study was to investigate the survival characteristics of verocytotoxigenic Escherichia coli (VTEC) and Salmonella in soil, slurry, farm water and bovine feces. Samples of each of the aforementioned media were inoculated with separate cocktails of VTEC and Salmonella and stored at 4 and 14 ºC, representing average Winter and Summer temperatures respectively. Samples were withdrawn periodically and surviving cells enumerated by directly plating onto selective media. Decimal reduction times (D-values) were calculated from the inverse of the slope obtained by linear regression of a plot of time versus the log of surviving cells. In the latter stages of the experiment, presence or absence was determined by enrichment and selective plating. VTEC and Salmonella D-values ranged from 3.59 to 23.84 days. Temperature significantly affected VTEC survival in water (P<0.05) and Salmonella survival in bovine feces (P<0.01) but not in any of the other farm media tested. In general there was no significant difference (P>0.001) between VTEC and Salmonella survival in a given medium under similar storage temperatures. However, Salmonella D-values were signiZcantly higher in slurry (4°C) and bovine feces (4°C and 14°C). This study provides critical comparative data on VTEC and Salmonella death rates in a range of environments commonly encountered on farms to support the development of quantitative microbial risk assessment (QMRA) and provide the scientiZc basis for an effective good agricultural practice (GAP) food safety program.

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