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 (kG and max population), and inactivation rates (D25 and D55) were investigated following exposures to simultaneous pH (3.0-8.0), aw (0.93-0.99) and temperature stresses (3.0-62 °C). Multiple regression analyses showed that % injury was significantly influenced by aw, aw2, and temperature while the lag times were influenced by pH, pH-temperature interaction, and aw-temperature interaction. The measured growth parameters were however, not significantly influenced by any of the stressors. Acid inactivation rates (D25) in apple juice were influenced by aw, pH-temperature interaction, and aw-temperature interaction; while the thermal inactivation rates (D55) in apple juice were influenced by pH and aw 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.