The inactivation and sublethal injury of Escherichia coli O157:H7, Campylobacter jejuni and Pseudomonas aeruginosa at three temperatures (22 °C, 4 °C and -18 °C) were studied using traditional microbiological tests and mid-infrared spectroscopy (4000-400 cm(-1)). Bacteria were cultivated in diluted nutrient matrices with a high initial inoculation (∼10(7) CFU/ml) levels. Both E. coli O157:H7 and P. aeruginosa survived and cell numbers increased at 22 °C for 5 days while C. jejuni numbers decreased one log(10) CFU/ml. A two log CFU/ml decrease was observed for the three pathogens held at 4 °C for 12 days. C. jejuni survived poorly following incubation at -18 °C for 20 days while levels of E. coli O157:H7 and P. aeruginosa remained high (10(4) CFU/ml). Temperature stress response of microbes was observed by infrared spectroscopy in polysaccharide, protein, lipid, and nucleic acid regions and was strain specific. Level of cold injury could be predicted using cluster, discriminant function and class analog analysis models. Pathogens may produce oligosaccharides and potentially other components in response to stress as indicated by changes in spectral features at 1200-900 cm(-1) following freezing.
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