Influence of Temperature and Predation on Survival of Salmonella enterica Serovar Typhimurium and Expression of invA in Soil and Manure-Amended Soil

Abstract

The effects of three temperatures (5, 15, and 25°C) on the survival of Salmonella enterica serovar Typhimurium in topsoil were investigated in small microcosms by three different techniques: plate counting, invA gene quantification, and invA mRNA quantification. Differences in survival were related to the effect of protozoan predation. Tetracycline-resistant Salmonella serovar Typhimurium was inoculated into soil and manure-amended soil at 1.5 ؋ 10 8 cells g soil ؊1 . Population densities were determined by plate counting and by molecular methods and monitored for 42 days. Simultaneous extraction of RNA and DNA, followed by quantitative PCR, was used to investigate invA gene levels and expression. Analysis by these three techniques showed that Salmonella serovar Typhimurium survived better at 5°C. Comparing DNA and CFU levels, significantly higher values were determined by DNA-based techniques. invA mRNA levels showed a fast decrease in activity, with no detectable mRNA after an incubation period of less than 4 days in any of the soil scenarios. A negative correlation was found between Salmonella serovar Typhimurium CFU levels and protozoan most probable numbers, and we propose the role of the predator-prey interaction as a factor to explain the die-off of the introduced strain by both culture-and DNA quantification-based methods. The results indicate that temperature, manure, and protozoan predation are important factors influencing the survival of Salmonella serovar Typhimurium in soil.

Salmonella and Fecal Indicator Bacteria Survival in Soils Amended with Poultry Manure

“…Key factors shown to impact bacterial survival include temperature, soil type, soil moisture, nutrient availability, and protection from UVexposure (Zibilske and Weaver 1978;Chandler and Craven 1980;Crane and Moore 1986;Guan and Holley 2003;Holley et al 2006;You et al 2006;Lang and Smith 2007;Garcia et al 2010). Bacterial survival in soils is also dependent on interactions with plants and plant roots, protozoan predators, and native microbial communities (Jiang et al 2002;Brandl et al 2005;You et al 2006;van Elsas et al 2007;Garcia et al 2010;Ibekwe et al 2010;Liang et al 2011;Rothrock et al 2012;Farhangi et al 2013;Erickson et al 2014). …”

Interaction between Salmonella and Plants: Potential Hosts and Vectors for Human Infection

“…In general, temperature has an important efect on growth and decay rates of bacteria. Most studies examined the inluence of temperature on survival of enteric bacteria under isothermal conditions, showing a generally reduced survival of Salmonella in soil with increasing temperature and, accordingly a beter persistence in soil at lower temperatures [36,37]. Semenov et al [38] analyzed how temperature luctuations afect Salmonella enterica serovar Typhimurium (S. Typhimurium) in cow manure and demonstrated increased decay rates with increasing amplitudes of daily oscillations.…”

“…Thompson was accumulated in vesicles of Tetrahymena [56], while growth of protozoa can also decimate S. Typhimurium populations [37].…”

Scientific Opinion on the risk posed by pathogens in food of non‐animal origin. Part 2 (Salmonella and Norovirus in leafy greens eaten raw as salads)

“…Salmonella was detected on cabbage leaves 120 days after manure application, but only for the highest level of Salmonella inoculated (10 7 CFU/g of manure). Salmonella declined when inoculated in soil amended manure, at rates that varied according to climate, and both the nature of the soil and the manure (Garcia et al, 2010;Natvig et al, 2002;Ongeng et al, 2011;Semenov et al, 2009). The risk of finding Salmonella on leafy greens grown on soil amended with contaminated manure decreases with the time between manure application and harvest.…”