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Thermal resistance of Clostridium difficile spores in ham and subsequent germination and outgrowth
This research was developed to study the heat-resistance of C. difficile spores to thermal injury and the subsequent germination and outgrowth in pork ham. In the first part of the project, thermal resistance of C. difficile spores in pork meat and water was determined by using two different procedures to recover heat-injured spores, the alkaline thioglycollate-lysozyme method and the taurocholate method. Higher spore recovery was observed with the lysozyme treatment at high temperatures (p<0.05) with D values ranging between 0.37 (90°C) and 29.31 h (70°C). Hypervirulence of the strains was not associated with an increased thermal resistance in meat. C. difficile spores can survive cooking practices for meat but conclusions regarding their thermal resistance can be misleading if the proper procedures to recover heat-injured organisms are not used. In the second part, it was observed that C. difficile spore germination and outgrowth after cooking (75°C, 20 min) occurred at temperatures between 20 and 40°C with generation times going from 1.11 h (37°C) to > 11 h (20°C). Incorporation of a germinant (taurocholate) into the meat confirmed that C. difficile spore germination occurs at a sub-optimal rate. Additionally, it was also observed that the capacity of C. difficile spores to germinate from meat could be impaired with moderate cooking procedures (80°C, 30 min). Growth data was used to develop a dynamic model to predict C. difficile spore germination and outgrowth in ham. In the last part, C. difficile spore germination and outgrowth in culture broth was evaluated within a range of various temperature (15-45°C), pH (4.5-8.5) and aw conditions (0.965-0.990). Results confirmed that C. difficile spore germination and outgrowth do not occur at pH and aw values below 4.5 and 0.965, respectively. Growth data from broth was used to develop a boundary model that confirmed a synergistic effect of temperature and pH or aw on C. difficile spore germination and outgrowth. Even though there is a low risk for C. difficile spore germination and outgrowth in meat, its spores can survive common cooking practices and the possibility of foodborne illness may still be high for at risk populations.
Redondo-Solano, Mauricio A, "Thermal resistance of Clostridium difficile spores in ham and subsequent germination and outgrowth" (2014). ETD collection for University of Nebraska - Lincoln. AAI3667155.