Heat resistance of Listeria monocytogenes by two recovery media used with and without cold preincubation.
Three strains of Listeria monocytogenes were heat-treated at three temperatures in physiological saline by a capillary tube method. Recovery of heat-treated bacteria was performed on blood agar and on tryptose phosphate agar with ferric citrate and aesculin (TPA-FE). Both media were used in two ways: (1) incubation at 37 degrees C for 7 d, and (2) preincubation at 4 degrees C for 5 d in order to obtain repair of heat-injured bacteria, followed by incubation at 37 degrees C for 7 d. D and z values were determined. In both incubation procedures, better average recovery was obtained on blood agar than on TPA-FE. Thus, higher D values were recorded when blood agar was used. In most cases the differences were statistically significant. Repair at 4 degrees C of heat-injured bacteria occurred on both media but the proportions of repaired bacteria were higher on blood agar. The repair on this medium was generally reflected in higher D values for preincubated samples. Some significant differences in heat resistance were noted between the strains.
Sörqvist
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Department of Food Hygiene, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, Uppsala.
D000362:Agar; D001431:Bacteriological Techniques; D015169:Colony Count, Microbial; D003470:Culture Media; D005069:Evaluation Studies as Topic; D006358:Hot Temperature; D008089:Listeria monocytogenes / Q000254:growth & development / Q000302:isolation & purification*; D013045:Species Specificity
D003470:Culture Media; D000362:Agar