Pathogenesis, growth and survival characteristics of Listeria monocytogenes - a newly emerged food-borne pathogen
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Survival and growth characteristics of Listeria monocytogenes isolates were determined in Tryptose Phosphate Broth and in chicken and beef substrates in the period 1993 to 1994. Observed generation times for the Scott A strain (clinical isolate) in Tryptose Phosphate Broth, anaerobically, were 146.2,21.0,16.5,8.2 and 1.6 hours at 0,3.5,5.5, 8.0 and 20°C, respectively, compared to 123.4,23.1,17.5,7.5 and 1.5 hours, aerobically. Similar growth rates were observed for strain RMIT 405 (raw chicken isolate), both anaerobically and aerobically in Tryptose Phosphate Broth, chicken and beef substrates. Growth rates were fitted to the square root model with a coefficient of determination (R2 value) of 98.36 to 99.48 percent. Heating to an internal temperature of 70°C resulted in a 3 to 5 log reduction of all L. monocytogenes isolates under study in broth and chicken substrates while a heat treatment to 70°C/2 minutes resulted in a reduction greater than 7 log cycles. Lowering the product pH to 5.0 was effective in inhibiting L. monocytogenes growth, whereas a sodium chloride concentration of 2 percent had a negligible effect on growth rates.