OCCURRENCE AND THERMO-RESISTANCE OF SPORES OF PSYCHROPHILIC AND PSYCHROTROPHIC AEROBIC SPOREFORMERS IN SOIL AND FOODS

Spores of psychrotrophic (able to grow at 5.degree. C) aerobic sporeformers [bacteria] occurred in soil in high numbers (2 .times. 103-5 .times. 106/g), but psychrophilic (able to grow at 0.degree. C) spores were present at significantly lower levels (500-105/g). Psychrotrophic spores were absent in herbs and spices; in pasteurized meals prepared industrially their numbers varied from < 10-1000/g. For spores harvested from Trypticase Soy Agar (TSA), the heat resistance of the cold-tolerant sporeformers was low with D90.degree.C [decimal reduction time] values from 1-11 min. The recovery of heated psychrophilic spores on this medium at 5.degree. C was equal to their recovery at 20.degree. C. The recovery of heated psychrotrophic spores was lower at 5.degree. C than at 20.degree. C, but unheated spores gave the same counts at both temperatures. The heat resistance of naturally occurring spores of cold-tolerant sporeformers washed from soil was comparable with the resistance of spores formed on TSA.