Fate of Salmonella enterica serovar Typhimurium on carrots and radishes grown in fields treated with contaminated manure composts or irrigation water

Abstract

Three different types of compost, PM-5 (poultry manure compost), 338 (dairy cattle manure compost), and NVIRO-4 (alkaline-pH-stabilized dairy cattle manure compost), and irrigation water were inoculated with an avirulent strain of Salmonella enterica serovar Typhimurium at 10(7) CFU g(-1) and 10(5) CFU ml(-1), respectively, to determine the persistence of salmonellae in soils containing these composts, in irrigation water, and also on carrots and radishes grown in these contaminated soils. A split-plot block design plan was used for each crop, with five treatments (one without compost, three with each of the three composts, and one without compost but with contaminated water applied) and five replicates for a total of 25 plots for each crop, with each plot measuring 1.8 x 4.6 m. Salmonellae persisted for an extended period of time, with the bacteria surviving in soil samples for 203 to 231 days, and were detected after seeds were sown for 84 and 203 days on radishes and carrots, respectively. Salmonella survival was greatest in soil amended with poultry compost and least in soil containing alkaline-pH-stabilized dairy cattle manure compost. Survival profiles of Salmonella on vegetables and soil samples contaminated by irrigation water were similar to those observed when contamination occurred through compost. Hence, both contaminated manure compost and irrigation water can play an important role in contaminating soil and root vegetables with salmonellae for several months.

FIG. 1.

Survival of S. enterica serovar Typhimurium in inoculated-compost-amended or inoculated-water-irrigated soil samples from fields used for growing carrots. Treatments included no compost (□), poultry manure compost (▪), dairy cattle manure compost (▴), alkaline-pH-stabilized dairy cattle manure compost (•), and contaminated irrigation water (○). The arrow indicates that the organism was not detectable by enrichment culture.

FIG. 2.

Survival of serovar Typhimurium in inoculated-compost-amended or inoculated-water-irrigated soil samples from fields used for growing radishes. Treatments included no compost (□), poultry manure compost (▪), dairy cattle manure compost (▴), alkaline-pH-stabilized dairy cattle manure compost (•), and contaminated irrigation water (○). The arrow indicates that the organism was not detectable by enrichment culture.

FIG. 3.

Survival of serovar Typhimurium on carrots grown in fields containing inoculated-compost-amended or inoculated-water-irrigated soil. Treatments included no compost (□), poultry manure compost (▪), dairy cattle manure compost (▴), alkaline-pH-stabilized dairy cattle manure compost (•), and contaminated irrigation water (○). Carrots were harvestable at day 149. The arrow indicates that the organism was not detectable by enrichment culture.

FIG. 4.

Survival of serovar Typhimurium on radishes grown in fields containing inoculated-compost-amended or inoculated-water-irrigated soil. Treatments included no compost (□), poultry manure compost (▪), dairy cattle manure compost (▴), alkaline-pH-stabilized dairy cattle manure compost (•), and contaminated irrigation water (○). Radishes were harvestable at day 57. The arrow indicates that the organism was not detectable by enrichment culture.