Influences of simultaneous physicochemical stress exposures on injury and subsequent responses of E. coli O157:H7 to resuscitative and inactivative challenges.
E. coli O157:H7 responses namely, sublethal injury (% injury), subsequent resuscitation (lag) and growth parameters (k(G) and max population), and inactivation rates (D(25) and D(55)) were investigated following exposures to simultaneous pH (3.0-8.0), a(w) (0.93-0.99) and temperature stresses (3.0-62 degrees C). Multiple regression analyses showed that % injury was significantly influenced by a(w), a(w)(2), and temperature while the lag times were influenced by pH, pH-temperature interaction, and a(w)-temperature interaction. The measured growth parameters were however, not significantly influenced by any of the stressors. Acid inactivation rates (D(25)) in apple juice were influenced by a(w), pH-temperature interaction, and a(w)-temperature interaction; while the thermal inactivation rates (D(55)) in apple juice were influenced by pH and a(w) stresses. Results also showed that % injury alone may not correctly predict the subsequent resuscitation rates of the test organism at favorable growth conditions. The nature of the injury contributed by a specific stressor also influenced resuscitation. The occurrence of injury and loss of cell viability did not induce acid stress adaptation to the organism. However, exposures to very low- and low pH conditions that resulted in injury and loss in cell viability induced thermal cross protection in E. coli O157:H7. The results obtained in the study contribute in further understanding the behavior of the test organism after exposure to combinations of stresses commonly encountered in food and food processing ecologies.
Gabriel
Alonzo A
AA
Laboratory of Food Microbiology and Hygiene, Department of Biofunctional Science and Technology, Graduate School of Biosphere Science, Hiroshima University, 1-4-4 Kagamiyama, Higashi-Hiroshima City, Hiroshima, 739-8528, Japan. alonzo.gabriel@gmail.com
Nakano
Hiroyuki
H
D001628:Beverages / Q000382:microbiology; D019453:Escherichia coli O157 / Q000254:growth & development*; D005511:Food Handling / Q000379:methods; D005516:Food Microbiology; D006863:Hydrogen-Ion Concentration; D027845:Malus / Q000382:microbiology; D050296:Microbial Viability; D012044:Regression Analysis; D013312:Stress, Physiological; D013696:Temperature