Effects of Cattle Feeding Regimen and Soil Management Type on the Fate of Escherichia coli O157:H7 and Salmonella enterica Serovar Typhimurium in Manure, Manure-Amended Soil, and Lettuce

Abstract

Survival of the green fluorescent protein-transformed human pathogens Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium was studied in a laboratory-simulated lettuce production chain. Dairy cows were fed three different roughage types: high-digestible grass silage plus maize silage (6:4), low-digestible grass silage, and straw. Each was adjusted with supplemental concentrates to high and low crude protein levels. The pathogens were added to manure, which was subsequently mixed (after 56 and 28 days for E. coli O157:H7 and Salmonella serovar Typhimurium, respectively) with two pairs of organically and conventionally managed loamy and sandy soil. After another 14 days, iceberg lettuce seedlings were planted and then checked for pathogens after 21 days of growth. Survival data were fitted to a logistic decline function (exponential for E. coli O157:H7 in soil). Roughage type significantly influenced the rate of decline of E. coli O157:H7 in manure, with the fastest decline in manure from the pure straw diet and the slowest in manure from the diet of grass silage plus maize silage. Roughage type showed no effect on the rate of decline of Salmonella serovar Typhimurium, although decline was significantly faster in the manure derived from straw than in the manure from the diet of grass silage plus maize silage. The pH and fiber content of the manure were significant explanatory factors and were positively correlated with the rate of decline. With E. coli O157:H7 there was a trend of faster decline in organic than in conventional soils. No pathogens were detected in the edible lettuce parts. The results indicate that cattle diet and soil management are important factors with respect to the survival of human pathogens in the environment.

Survival of Escherichia coli in the environment: fundamental and public health aspects

“…This suggested that the organism possibly uses combined mechanisms or even as-yet-unidentified alternative mechanisms. Strikingly, particular E. coli O157:H7 strains almost appeared as acidiphiles, as their survival was higher at low pH than at relatively high pH (Franz et al, 2005). However, a significant variation in the ability to survive in low-pH environments was found among isolates within a single serotype (Buchanan and Edelson, 1999).…”

“…In an animal host body, temperature is often stable, whereas it may be strongly fluctuating in a non-host environment such as soil or water. Until recently, the effect of fluctuating temperature on E. coli survival and adaptation (compared with stable temperatures) in soil was poorly understood, as previous survival experiments had all been carried out under temperature-stable conditions (Kudva et al, 1998;Himathongkham et al, 1999;Franz et al, 2005). Recent results obtained with E. coli O157:H7 showed that survival in manure under fluctuating temperatures was generally lower than that under constant temperature (Semenov et al, 2007).…”

“…In the light of these differences, the survival of the two species in open environments has been shown to be different. Thus Salmonella strains survived significantly longer in terrestrial habitats in the majority of cases in comparison to E. coli strains (Himathongkham et al, 1999;Franz et al, 2005;Semenov et al, 2007). Such differential survival might relate to genome size or content or gene expression patterns between the two species.…”

Microbial diversity determines the invasion of soil by a bacterial pathogen

“…Microcosms were inoculated with the assemblages at similar final cell densities (OD 600 = 0.1). Thus, each microcosm received the species at a cell density of OD 600 = 0.1/s, where s is the number of species in the community inoculum (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). For microcosms containing strain T, the latter was introduced at OD 600 = 0.02, regardless of the established species richness.…”

“…The fate of the enterohemorrhagic Escherichia coli (EHEC) O157:H7 in soil is of major concern (18)(19)(20). In this context, the microbial communities that established after soil fumigation were shown to determine the fate of the invading species, whereby reduction in microbial diversity due to progressively enhanced fumigation depths resulted in higher pathogen persistence in soil (21).…”