THE FATE OF BACILLUS-ANTHRACIS IN UNPASTEURIZED AND PASTEURIZED MILK

Events following the inoculation of vegetative and spore forms of Bacillus anthracis into unpasteurized and pasteurized milk were monitored at 37-degrees-C, room temperature (RT; 20 +/- 2-degrees-C) and in a refrigerator (5-9-degrees-C). Counts of vegetative B. anthracis decreased rapidly in both unpasteurized and pasteurized milk, becoming undetectable by 7 h at 37-degrees-C and by 24 h at RT and in the refrigerator. Spores in unpasteurized milk showed no significant signs of gemination after 48 h. In pasteurized milk, there was a slight overall increase (+/- 1 log) in total and spore counts at 37-degrees-C; at RT there was an overall fall (1.5-2 logs) and in the refrigerator, total counts remained steady while spore counts fell 1 log over a 48 h period. The frequently observed rise in counts of endogenous (presumptively identified) B. cereus from undetectable to > 10(6)/ml at 37-degrees-C and > 10(5)/ml at RT by 24 h contrasted with the behaviour exhibited by the vegetative B. anthracis.