Acid-adaptation does not increase the resistance of Listeria monocytogenes to irradiation in a seafood salad

• Published in: International journal of food microbiology Vol. 99; no. 2; pp. 147 - 156
• Main Authors: Foley, D.M, Trimboli, S.L, Lamb, J, Gogley, J, Thompson, J, Caporaso, F, Calicchia, M, Prakash, A
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier 15.03.2005
• Subjects: acetic acid; Acetic Acid - pharmacology; acid tolerance; Adaptation, Physiological - drug effects; aerobes; aerobic plate count; bacterial contamination; Biological and medical sciences; citric acid; Citric Acid - pharmacology; Colony Count, Microbial; Fish and seafood industries; flavor; food contamination; Food Handling - methods; Food industries; Food Irradiation; Food Microbiology; food pathogens; food storage; Fundamental and applied biological sciences. Psychology; gamma radiation; Gamma Rays; Hydrogen-Ion Concentration; lactic acid; Lactic Acid - pharmacology; Listeria monocytogenes; Listeria monocytogenes - growth & development; Listeria monocytogenes - physiology; Listeria monocytogenes - radiation effects; molds (fungi); off odors; plate count; psychrotrophic bacteria; radiation resistance; refrigeration; salads; Seafood - microbiology; seafoods; sensory evaluation; shelf life; storage time; strains; stress adaptation; stress hardening; stress tolerance; taste; texture; yeasts; Resistance; Stress hardening; Stress adaptation; Irradiation; Listeria monocytogenes; Seafood; Bacteria; Seafood salad; Salad; Sensory testing; Adaptation
• ISSN: 0168-1605; 1879-3460
• DOI: 10.1016/j.ijfoodmicro.2004.07.018

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.