title: Acid-adaptation does not increase the resistance of Listeria monocytogenes to irradiation in a seafood salad.
abstract: Stress adaptation of microbial cells enables the cells to survive better when they are subsequently exposed to other types of stresses. In the food industry, pathogens are commonly stressed during food processing and this is a concern where pathogens such as Listeria monocytogenes are involved. Research was conducted to determine if acid adaptation of L. monocytogenes provides resistance to ionizing irradiation. Three different strains of L. monocytogenes were acid-adapted using three different acids (acetic, citric, lactic) in Tryptic Soy Broth, at a pH 5.5 for 1 h, 4 h, or continuous acid exposure. The acid-adapted L. monocytogenes were then exposed to a low level of gamma irradiation (0.59-0.72 kGy) along with a non-acid adapted L. monocytogenes control. In a test tube study, the 1-h acetic acid-adapted L. monocytogenes strains showed the greatest difference from the control, a reduced kill of 1.1 log CFU/g but this difference was not significant by ANOVA (p=0.054). The reduction achieved after 4 h and continuous acid exposure also did not significantly differ from the control. To determine whether acid adaptation affected radiation resistance within a food product, a refrigerated storage shelf-life study was completed. Acetic acid was used to acid adapt a three-strain cocktail of L. monocytogenes for a period of 1 h. The organisms were then inoculated into a seafood salad (pH 5.15) and subsequently exposed to low dose gamma irradiation (0.7 to 4.5 kGy). L. monocytogenes was reduced or eliminated by irradiation regardless of acid adaptation; no increased resistance was observed.
authors.affiliation: Department of Biological Sciences, Chapman University, Orange, CA 92866, USA. dfoley@chapman.edu
authors.forename: D M
authors.initials: DM
authors.lastname: Foley
authors.forename: S L
authors.initials: SL
authors.lastname: Trimboli
authors.forename: J
authors.initials: J
authors.lastname: Lamb
authors.forename: J
authors.initials: J
authors.lastname: Gogley
authors.forename: J
authors.initials: J
authors.lastname: Thompson
authors.forename: F
authors.initials: F
authors.lastname: Caporaso
authors.forename: M
authors.initials: M
authors.lastname: Calicchia
authors.forename: A
authors.initials: A
authors.lastname: Prakash
mesh_terms: D019342:Acetic Acid / Q000494:pharmacology; D000222:Adaptation, Physiological / Q000187:drug effects; D019343:Citric Acid / Q000494:pharmacology; D015169:Colony Count, Microbial; D005511:Food Handling / Q000379:methods; D005514:Food Irradiation; D005516:Food Microbiology; D005720:Gamma Rays; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000494:pharmacology; D008089:Listeria monocytogenes / Q000254:growth & development / Q000502:physiology / Q000528:radiation effects*; D017747:Seafood / Q000382:microbiology*
chemical_list: D019343:Citric Acid; D019344:Lactic Acid; D019342:Acetic Acid