Towards microbiological quality assurance in radiation sterilization processing: the limiting case model applied to a microbial population having a distribution of radiation responses.

A limiting case model, developed earlier to provide a conservative estimate of the proportion of non-sterile items (P) in an irradiated population of items contaminated with micro-organisms of a single type, has been extended to include items having organisms of different types. Estimates of P are compared with exact values derived on purely theoretical grounds and with values obtained by computer simulation of microbiological inactivation on items.

Net positives: conservative approach to measurement of proportions positive in substerilization process studies.

A method (designated the net positive approach) is described for scoring results of sterility tests done with more than one recovery condition on product items treated with inactivating agents at levels less than those used in sterilization processes proper (subprocess treatments). Three tests of sterility, one per recovery condition, constitute a single sample. A growth in one or more recovery conditions is scored as a net positive for that sample. The net positive approach reduces the occurrence of false-negatives and assigns a value to the proportion of items reported as nonsterile (proportions positive) that is conservative.

Effects of processing and gamma irradiation on the microbiological contaminants of a laboratory animal diet.

The numbers and types of microorganisms contaminating a commercially available laboratory animal diet were examined by plate-count methods at all stages of production. During the cooking and pelleting stages of manufacture there was a marked reduction in numbers of heat-labile vegetative contaminants introduced via the raw materials, and at subsequent stages plate counts at 37 and 25 degrees C corresponded closely to counts of viable aerobic bacterial endospores. It would seem that the count on the pelleted diet was determined principally by the numbers of bacterial spores being introduced with the ingredients. The response to gamma-irradiation of the innate microflora contaminating the pelleted diet was characteristic of that generally seen with populations of aerobic bacterial endospores.

Factors affecting the production of sterigmatocystin in semisynthetic media.

Production of sterigmatocystin by Aspergillus versicolor was stimulated by inorganic phosphate when used in conjunction with citric acid cycle compounds.

Potential production of sterigmatocystin on country-cured ham.

In laboratory media, 10 of 16 isolates of Aspergillus versicolor from country-cured ham were capable of producing sterigmatocystin. Three of these isolates were tested and found to produce sterigmatocystin on country-cured ham after 14 days of incubation at 20 or 28 C.