title: Role of initial contamination levels, biofilm maturity and presence of salt and fat on desiccation survival of Listeria monocytogenes on stainless steel surfaces.
abstract: This study investigated the effect of initial contamination levels, biofilm maturity and presence of salt and fatty food soils on desiccation survival of Listeria monocytogenes on stainless steel (SS) coupons. L. monocytogenes cultures grown (at 15 °C for 48 h) in Tryptic Soy Broth with 1% glucose (TSB-glu) containing either 0.5 or 5% (w/v) NaCl were re-suspended in TSB-glu containing either 0.5 or 5% NaCl and used to contaminate SS coupons at levels of 3.5, 5.5, and 7.5 log CFU/cm². Desiccation (at 15 °C for 20 days, 43% RH) commenced immediately (non-biofilm) or following biofilm formation (at 15 °C for 48 h, 100% RH). To study the impact of food lipids, non-biofilm L. monocytogenes cells were suspended in TSB-glu containing either canola oil (5-10%) or lard (20-60%) and desiccated as above on SS coupons. Following desiccation for 20 days, survivors decreased by 1.4-3.7 log CFU/cm² for non-biofilm L. monocytogenes cells. The contamination level had no significant (p > 0.05) effect on survival kinetics. SEM micrographs showed mature biofilms on coupons initially contaminated with 5.5 and 7.5 log CFU/cm². Mature biofilm cells were significantly (p < 0.05) more desiccation resistant than cells in immature biofilms formed by the lowest contamination level. Besides biofilm maturity/formation, previous osmoadaptation, exposure to lard (20-60%) or salt (5%) during desiccation significantly (p < 0.05) increased the bacterium's survival. In conclusion, L. monocytogenes desiccation survival can be greatly reduced by preventing presence of mature biofilms and salty or fatty soils on food contact surfaces.
authors.affiliation: Department of Process Engineering and Applied Science, Dalhousie University, 1360 Barrington Street, Halifax, NS B3H 4R2, Canada.
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Hingston
authors.forename: Emma C
authors.initials: EC
authors.lastname: Stea
authors.forename: Susanne
authors.initials: S
authors.lastname: Knøchel
authors.forename: Truelstrup
authors.initials: T
authors.lastname: Hansen
mesh_terms: D018441:Biofilms; D003890:Desiccation; D004866:Equipment Contamination; D057140:Fast Foods / Q000032:analysis / Q000382:microbiology*; D005223:Fats / Q000032:analysis*; D005506:Food Contamination / Q000032:analysis*; D061353:Food Storage / Q000295:instrumentation; D008089:Listeria monocytogenes / Q000737:chemistry / Q000187:drug effects / Q000254:growth & development* / Q000502:physiology; D050296:Microbial Viability; D008954:Models, Biological; D012965:Sodium Chloride / Q000032:analysis* / Q000494:pharmacology; D013193:Stainless Steel / Q000032:analysis*
chemical_list: D005223:Fats; D013193:Stainless Steel; D012965:Sodium Chloride