title: Thermal Resistance and Gene Expression of both Desiccation-Adapted and Rehydrated Salmonella enterica Serovar Typhimurium Cells in Aged Broiler Litter.
abstract: The objective of this study was to investigate the thermal resistance and gene expression of both desiccation-adapted and rehydratedSalmonella entericaserovar Typhimurium cells in aged broiler litter.STyphimurium was desiccation adapted in aged broiler litter with a 20% moisture content (water activity [aw], 0.81) for 1, 2, 3, 12, or 24 h at room temperature and then rehydrated for 3 h. As analyzed by quantitative real-time reverse transcriptase PCR (qRT-PCR), therpoS,proV,dnaK, andgrpEgenes were upregulated (P< 0.05) under desiccation stress and could be induced after 1 h but in less than 2 h. Following rehydration, fold changes in the levels of these four genes became significantly lower (P< 0.05). The desiccation-adapted ΔrpoSmutant was less heat resistant at 75°C than was the desiccation-adapted wild type (P< 0.05), whereas there were no differences in heat resistance between desiccation-adapted mutants in two nonregulated genes (otsAand PagfD) and the desiccation-adapted wild type (P> 0.05). Survival characteristics of the desiccation-adapted ΔPagfD(rdar [red, dry, and rough] morphotype) and ΔagfD(saw [smooth and white] morphotype) mutants were similar (P> 0.05). Trehalose synthesis in the desiccation-adapted wild type was not induced compared to a nonadapted control (P> 0.05). Our results demonstrated the importance of therpoS,proV,dnaK, andgrpEgenes in the desiccation survival ofSTyphimurium. By using an ΔrpoSmutant, we found that therpoSgene was involved in the cross-protection of desiccation-adaptedSTyphimurium against high temperatures, while trehalose synthesis or rdar morphology did not play a significant role in this phenomenon. In summary,STyphimurium could respond rapidly to low-awconditions in aged broiler litter while developing cross-protection against high temperatures, but this process could be reversed upon rehydration.IMPORTANCEPhysical heat treatment is effective in eliminating human pathogens from poultry litter used as biological soil amendments. However, prior to physical heat treatment, some populations of microorganisms may be adapted to the stressful conditions in poultry litter during composting or stockpiling, which may cross-protect them against subsequent high temperatures. Our previous study demonstrated that desiccation-adaptedS. entericacells in aged broiler litter exhibited enhanced thermal resistance. However, there is limited research on the underlying mechanisms of the extended survival of pathogens under desiccation conditions in animal wastes and cross-tolerance to subsequent heat treatment. Moreover, no information is available about the thermal resistance of desiccation-adapted microorganisms in response to rehydration. Therefore, in the present study, we investigated the gene expression and thermal resistance of both desiccation-adapted and rehydratedSTyphimurium in aged broiler litter. This work will guide future research efforts to control human pathogens in animal wastes used as biological soil amendments.
authors.affiliation: Department of Biological Sciences, Clemson University, Clemson, South Carolina, USA.
authors.forename: Zhao
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Department of Food, Nutrition, and Packaging Sciences, Clemson University, Clemson, South Carolina, USA xiuping@clemson.edu.
authors.forename: Xiuping
authors.initials: X
authors.lastname: Jiang
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002645:Chickens; D003890:Desiccation; D006358:Hot Temperature; D008372:Manure / Q000032:analysis / Q000382:microbiology*; D050296:Microbial Viability; D012486:Salmonella typhimurium / Q000737:chemistry* / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D014867:Water / Q000032:analysis / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D008372:Manure; D014867:Water
keywords: Salmonella enterica serovar Typhimurium; desiccation; gene expression; poultry litter; rdar morphotype; rehydration; thermal resistance