THE EFFECT OF RECOVERY CONDITIONS ON THE APPARENT HEAT-RESISTANCE OF BACILLUS-CEREUS SPORES

The effect of recovery media and incubation temperature on the apparen t heat resistance of three ATCC strains (4342, 7004 and 9818) of Bacil lus cereus spores were studied. Nutrient Agar (NA), Tryptic Soy Agar ( TSA), Plate Count Agar (PCA) and Milk Agar (MA) as the media and tempe ratures in the range of 15-40 degrees C were used to recover heated sp ores. Higher counts of heat injured spores were obtained on PCA and NA . The optimum subculture temperature was about 5 degrees C below the o ptimum temperature for unheated spores. No significant differences in heat resistance were observed with the different recovery conditions e xcept for strains 4342 and 9818 when MA was used as plating medium. La rge differences in D-values were found among the strains (D-100 = 0.28 min for 7004; D-100 = 0.99 min for 4342; D-100 = 4.57 min for 9818). The 7004 strain showed a sub-population with a greater heat resistance . The z values obtained for the three strains studied under the differ ent recovery conditions were similar (7.64 degrees C + 0.25).