Study suggests solarised sandy soils shorten Salmonella survival
Salmonella enterica is an important food-borne pathogen. It’s the second leading cause of notified food-borne illness in Australia, and is of significant concern to consumers, agricultural and food industries and public health agencies.
During the past three decades, there has been a rise in the incidence of outbreaks of S. enterica associated with the consumption of fresh fruit and vegetables. Contamination of cropping soils usually occurs through the use of raw or uncomposted manures, contaminated irrigation water or incursion of animals in the field. These soils consequently have the potential to contaminate fresh produce through soil contact or through rain or irrigation splash and pose a significant threat to food safety, especially of leafy greens.
Through its Vegetable Fund, Hort Innovation has recently funded the first research study investigating survival of S. enterica in soil contaminated with chicken manure conducted under Australian conditions. The research investigated the effect of soil type, temperature, moisture and presence (or absence) of chicken manure on the pathogen’s survival. It also examined two potential short-term remediation strategies to reduce levels of the bacteria in soil following contamination: cover cropping and/or solarisation.
The project research indicated that under natural field conditions, S. enterica counts decline over time after a contamination event. However, the rate of decline is significantly slower in clay loam soils, and is reduced by the presence of chicken manure, by soil temperatures less than 37⁰C, and by the presence of moisture. In the field trial, the bacteria was detectable up to 100 days after contaminated chicken manure was incorporated into clay loam soil.
In contrast, populations quickly declined within four weeks in sandy soils, at temperatures above 37⁰C and in soil without chicken manure as a source of energy.
The research also found that solarisation (black plastic covering the soil) may have potential to promote faster die-off of S. enterica, providing soil temperatures under the plastic have several hours at 37⁰C or above.
Further research is required to fully explore the value of cover cropping as a remediation strategy and to determine the amount of biomass and biofumigant levels required in the soil for die-off of the bacteria, and how quickly this could occur.