title: Cross-protection between controlled acid-adaptation and thermal inactivation for 48 Escherichia coli strains.
abstract: Given the importance of pH reduction and thermal treatment in food processing and food preservation strategies, the cross-protection between acid adaptation and subsequent thermal inactivation for 48 Escherichia coli strains was investigated. Those strains were selected among 188 E. coli strains according to their odds of growth under low pH conditions as determined by Haberbeck et al. (2015) [Haberbeck, L.U., Oliveira, R.C., Vivijs, B., Wenseleers, T., Aertsen, A., Michiels, C., Geeraerd, A.H., 2015. Variability in growth/no growth boundaries of 188 different Escherichia coli strains reveals that approximately 75% have a higher growth probability under low pH conditions than E. coli O157:H7 strain ATCC 43888. Food Microbiol. 45, 222-230]. E. coli cells were acid and nonacid-adapted during overnight growth in controlled acidic pH (5.5) and neutral pH (7.0), respectively, in buffered Lysogenic Broth (LB). Then, they were heat inactivated at 58°C in non-buffered LB adjusted to pH6.2 and 7.0. Thus, four conditions were tested in total by combining the different pH values during growth/thermal inactivation: 5.5/6.2, 5.5/7.0, 7.0/6.2 and 7.0/7.0. Acid adaptation in buffered LB at pH5.5 increased the heat resistance of E. coli strains in comparison with nonacid-adaptation at pH7.0. For instance, the median D58-value of strains inactivated at pH7.0 was approximately 6 and 4min for acid-adapted and nonacid-adapted strains, respectively. For the nonacid-adapted strains, the thermal inactivation at pH6.2 and 7.0 was not significantly (p=0.06) different, while for the acid-adapted strains, the thermal treatment at pH6.2 showed a higher heat resistance than at pH7.0. The correlation between the odds of growth under low pH previously determined and the heat resistance was significant (p<0.05). Remarkably, a great variability in heat resistance among the strains was observed for all pH combinations, with D58-values varying between 1.0 and 69.0min. In addition, highly heat resistant strains were detected. Those strains exhibited D58-values between 17.6 and 69.0min, while E. coli O157:H7 (ATCC 43888) showed D58-values between 1.2 and 3.1min. In summary, results clearly showed that adaptation of E. coli cells to constant acidic pH results in cross-protection against thermal inactivation.
authors: Laboratory of Food Microbiology, KU Leuven, Kasteelpark Arenberg 22, B-3001 Leuven, Belgium; MeBioS, Department of Biosystems (BIOSYST), Faculty of Bioscience Engineering, KU Leuven, Leuven, Belgium.
authors: Leticia Ungaretti
authors: LU
authors: Haberbeck
authors: Laboratory of Food Microbiology and Food Preservation, Department of Food Safety and Food Quality, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium.
authors: Xiang
authors: X
authors: Wang
authors: Laboratory of Food Microbiology, KU Leuven, Kasteelpark Arenberg 22, B-3001 Leuven, Belgium.
authors: Chris
authors: C
authors: Michiels
authors: Laboratory of Food Microbiology and Food Preservation, Department of Food Safety and Food Quality, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium.
authors: Frank
authors: F
authors: Devlieghere
authors: Laboratory of Food Microbiology and Food Preservation, Department of Food Safety and Food Quality, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium.
authors: Mieke
authors: M
authors: Uyttendaele
authors: MeBioS, Department of Biosystems (BIOSYST), Faculty of Bioscience Engineering, KU Leuven, Leuven, Belgium. Electronic address: Annemie.Geeraerd@kuleuven.be.
authors: Annemie H
authors: AH
authors: Geeraerd
mesh_terms: D000143:Acids / Q000494:pharmacology*; D000222:Adaptation, Physiological; D015169:Colony Count, Microbial; D004926:Escherichia coli / Q000737:chemistry / Q000187:drug effects* / Q000254:growth & development / Q000502:physiology*; D005511:Food Handling / Q000379:methods; D005516:Food Microbiology; D005519:Food Preservation / Q000379:methods; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration
chemical_list: D000143:Acids
keywords: D-value; Linear mixed model; Strain variability