Survival and Growth of Wild-Type and rpoS-Deficient Salmonella Newport Strains in Soil Extracts Prepared with Heat-Treated Poultry Pellets

Manoj K Shah; Rhodel Bradshaw; Esmond Nyarko; Patricia D Millner; Deborah Neher; Thomas Weicht; Teresa M Bergholz; Manan Sharma

doi:10.4315/0362-028X.JFP-18-465

Survival and Growth of Wild-Type and rpoS-Deficient Salmonella Newport Strains in Soil Extracts Prepared with Heat-Treated Poultry Pellets

J Food Prot. 2019 Mar;82(3):501-506. doi: 10.4315/0362-028X.JFP-18-465.

Authors

Manoj K Shah¹, Rhodel Bradshaw², Esmond Nyarko², Patricia D Millner², Deborah Neher³, Thomas Weicht³, Teresa M Bergholz¹, Manan Sharma²

Affiliations

¹ 1 Department of Microbiological Sciences, North Dakota State University, Fargo, North Dakota 48102.
² 2 U.S. Department of Agriculture, Agricultural Research Service, Northeast Area, Beltsville Agricultural Research Center, Environmental Microbial Food Safety Laboratory, Beltsville, Maryland 20705 (ORCID: http://orcid.org/000-0002-8585-0308 [M.S.]).
³ 3 Department of Plant and Soil Science, University of Vermont, Burlington, Vermont 05405, USA.

PMID: 30810379
DOI: 10.4315/0362-028X.JFP-18-465

Abstract

Manure runoff can transfer pathogens to farmlands or to water sources, leading to subsequent contamination of produce. Untreated biological soil amendments, like manure, can be contaminated with foodborne pathogens, such as Salmonella Newport, which may lead to transfer of the pathogen to fruits or vegetables. Studies have reported the occurrence and survival of Salmonella in manure or manure slurries. However, data on the survival and growth of Salmonella Newport is lacking in matrices simulating runoff. We quantified the survival and growth of wild-type (WT) Salmonella Newport and rpoS-deficient (Δ rpoS) strains in sterile and nonsterile soil extracts prepared with (amended) or without (unamended) heat-treated poultry pellets at 25°C. Salmonella Newport WT and Δ rpoS populations reached a maximum cell density of 6 to 8 log CFU/mL in 24 to 30 h in amended and unamended soil extracts and remained in stationary phase for up to 4 days. Salmonella Newport in amended soil extracts exhibited a decreased lag phase (λ , 2.87 ± 1.01 h) and greater maximum cell densities ( N_max, 6.84 ± 1.25 CFU/mL) compared with λ (20.10 ± 9.53 h) and N_max (5.22 ± 0.82 CFU/mL) in unamended soil extracts. In amended soil extract, the Δ rpoS strain had no measurable λ , similar growth rates (μ_max) compared with WT, and a lower N_max compared with the WT strain. Unamended, nonsterile soil extracts did not support the growth of Salmonella Newport WT and led to a decline in populations for the Δ rpoS strain. Salmonella Newport had lower cell densities in nonsterile soil extracts (5.94 ± 0.95 CFU/mL) than it did in sterile soil extracts (6.66 ± 1.50 CFU/mL), potentially indicating competition for nutrients between indigenous microbes and Salmonella Newport. The most favorable growth conditions were provided by amended sterile and nonsterile soil extracts, followed by sterile, unamended soil extracts for both Salmonella Newport strains. Salmonella Newport may grow to greater densities in amended extracts, providing a route for increased Salmonella levels in the growing environments of produce.

Keywords: Newport; Biological soil amendments; Heat-treated poultry pellets; Runoff; Soil extract.

MeSH terms

Animals
Crops, Agricultural / microbiology*
Food Contamination
Hot Temperature
Manure / microbiology*
Poultry
Salmonella / growth & development*
Soil
Soil Microbiology*

Substances

Manure
Soil