title: Role of sigB and osmolytes in desiccation survival of Listeria monocytogenes in simulated food soils on the surface of food grade stainless steel.
abstract: This research aimed to determine whether the SigB (σ(B)) regulon and osmolytes impact the survival of the foodborne pathogen, Listeria monocytogenes, during desiccation in simulated food soils with varying salt and nutrient contents on food grade stainless steel (SS) surfaces. L. monocytogenes 568 (Lm568, serotype 1/2a), its isogenic sigB mutant (ΔsigB) and the back-complemented ΔsigB were desiccated in BHI, TSB with 1% glucose (TSB-glu), peptone physiological saline (PPS) and minimal media (MM) for 21 days at 43% relative humidity (RH) and 15 °C on SS. The effect of food related osmolytes (proline, betaine and carnitine) on desiccation survival was studied by (a) pre-culturing strains in MM with an osmolyte followed by desiccation in MM and (b) by desiccating strains in MM with an osmolyte. Desiccation survival of L. monocytogenes was positively correlated to the nutrient and osmolyte concentrations in the desiccation substrates. Initial Lm568 levels of 8 Log(CFU/cm(2)) decreased by 0.9 Log(CFU/cm(2)) in BHI and 1.1-2.9 Log(CFU/cm(2)) in TSB-glu, PPS and MM after 21 days. Comparatively, the initial survival of ΔsigB was reduced in PS and MM, while no differences were observed among the three strains in BHI and TSB-glu. Pre-culture in osmolyte containing MM enhanced (p < 0.05) desiccation survival of all strains. Desiccation in osmolyte-containing MM improved desiccation survival of all strains, albeit the protection was less than that observed after pre-culture with the osmolytes. Complementation of the ΔsigB mutant restored the wildtype phenotype. In conclusion, this work shows the protective effect of osmolytes in desiccation survival of L. monocytogenes, while the σ(B) regulon only improved the initial survival in nutrient and osmolyte poor environments.
authors.affiliation: Department of Process Engineering and Applied Science, Dalhousie University, 1360 Barrington Street, Halifax, NS, B3H 4R2, Canada.
authors.forename: Yannan
authors.initials: Y
authors.lastname: Huang
authors.affiliation: Agriculture and Agri-Food Canada, Atlantic Food and Horticulture Research Centre, 32 Main Street, Kentville, NS, B4N 1J5, Canada.
authors.forename: Timothy C
authors.initials: TC
authors.lastname: Ells
authors.affiliation: Department of Process Engineering and Applied Science, Dalhousie University, 1360 Barrington Street, Halifax, NS, B3H 4R2, Canada. Electronic address: ltruelst@dal.ca.
authors.forename: Lisbeth
authors.initials: L
authors.lastname: Truelstrup Hansen
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001622:Betaine / Q000494:pharmacology; D002331:Carnitine / Q000494:pharmacology; D003890:Desiccation / Q000295:instrumentation / Q000379:methods; D005503:Food Additives / Q000494:pharmacology*; D005511:Food Handling / Q000295:instrumentation / Q000379:methods; D008089:Listeria monocytogenes / Q000187:drug effects / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D050296:Microbial Viability / Q000187:drug effects; D008954:Models, Biological; D009994:Osmolar Concentration; D011392:Proline / Q000494:pharmacology; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*; D012965:Sodium Chloride / Q000378:metabolism*; D013193:Stainless Steel / Q000032:analysis
chemical_list: D001426:Bacterial Proteins; D005503:Food Additives; C079011:SigB protein, Bacteria; D012808:Sigma Factor; D013193:Stainless Steel; D001622:Betaine; D012965:Sodium Chloride; D011392:Proline; D002331:Carnitine
keywords: Desiccation stress; Listeria monocytogenes; Osmolytes; Osmotic stress; Salt; SigB regulon; Stainless steel; Stress response