title: Survival and growth of epidemically successful and nonsuccessful Salmonella enterica clones after freezing and dehydration.
abstract: The spread of epidemically successful nontyphoidal Salmonella clones has been suggested as the most important cause of salmonellosis in industrialized countries. Factors leading to the emergence of success clones are largely unknown, but their ability to survive and grow after  physical stress may contribute. During epidemiological studies, a mathematical model was developed that allowed estimation of a factor (q) accounting for the relative ability of Salmonella serovars with different antimicrobial resistances to survive in the food chain and cause  human disease. Based on this q-factor, 26 Salmonella isolates were characterized as successful or nonsuccessful. We studied the survival and growth of stationary- and exponential-phase cells of these isolates after freezing for up to 336 days in minced meat. We also investigated  survival and growth after dehydration at 10°C and 82% relative humidity (RH) and 25°C and 49% RH for 112 days. Stationary-phase cells were reduced by less than 1 log unit during 1 year of freezing, and growth was initiated with an average lag phase of 1.7 h. Survival was lower in exponentialphase  cells, but lag phases tended to be shorter. High humidity and low temperature were less harmful to Salmonella than were low humidity and high temperature. Tolerance to adverse conditions was highest for Salmonella Infantis and one Salmonella Typhimurium U292 isolate and  lowest for Salmonella Derby and one Salmonella Typhimurium DT170 isolate. Dehydration, in contrast to freezing, was differently tolerated by the Salmonella strains in this study, but tolerance to freezing and dehydration does not appear to contribute to the emergence of  successful Salmonella clones.
authors.affiliation: National Food Institute, Technical University of Denmark, Kemitorvet 204, 2800 Kgs. Lyngby, Denmark. karom@food.dtu.dk
authors.forename: Karoline
authors.initials: K
authors.lastname: Müller
authors.forename: Søren
authors.initials: S
authors.lastname: Aabo
authors.forename: Tina
authors.initials: T
authors.lastname: Birk
authors.forename: Hanne
authors.initials: H
authors.lastname: Mordhorst
authors.forename: Björg
authors.initials: B
authors.lastname: Bjarnadóttir
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Agersø
mesh_terms: D015169:Colony Count, Microbial; D003890:Desiccation; D005506:Food Contamination / Q000517:prevention & control*; D005516:Food Microbiology; D005519:Food Preservation / Q000379:methods; D005615:Freezing; D006801:Humans; D007700:Kinetics; D008461:Meat Products / Q000382:microbiology*; D050296:Microbial Viability; D012478:Salmonella Food Poisoning / Q000517:prevention & control; D019779:Salmonella enterica / Q000254:growth & development*