Effect of low-dose irradiation on growth of and toxin production by Staphylococcus aureus and Bacillus cereus in roast beef and gravy.

The effect of irradiation (2 kGy) on growth of and toxin production by Staphylococcus aureus and Bacillus cereus in roast beef and gravy during storage at abuse temperatures (15 and 22 degrees C) was assessed by inoculation studies. Irradiation resulted in a 3-4 log10 reduction in numbers of both pathogens. Whenever B. cereus and S. aureus numbers reached 10(6) and 10(7) cfu/g, respectively, during storage their toxins were detectable. As the time taken to attain these levels was longer in irradiated than in unirradiated samples, toxin production by both pathogens was delayed by irradiation. When samples initially containing low levels (10(2)/g) of S. aureus were irradiated no toxin was produced during subsequent storage at 15 or 22 degrees C. Diarrhoeal toxin produced by B. cereus was detected after 2 days at 22 degrees C, but not at 15 degrees C, in samples containing 10(2) cells/g prior to irradiation. When higher numbers (10(6)/g) of either pathogen were present prior to irradiation, toxins were produced by both pathogens at 22 degrees C, but not at 15 degrees C. Microbial competition had an effect on the growth of B. cereus and S. aureus after irradiation when a low initial inoculum was applied. However, when a higher inoculum was used the pathogens outnumbered their competitors and competition effects were less important. It was concluded that low-dose irradiation would improve the microbiological safety of roast beef and gravy.

Lung volumes in healthy nonsmoking adults.

Total lung capacity (TLC), functional residual capacity, residual volume, and corresponding 95% confidence intervals were measured in 245 healthy nonsmoking person (122 women, 123 men) using a single-breath helium technique. Prediction equations for lung volumes were generated by multiple linear regression. The resultant equations are similar to previously published equations using multiple-breath gas equilibration techniques. Measured 95% confidence intervals can be closely approximated by using two times the standard error of the estimate for each equation, but cannot be approximated by using +/- 20% of the predicted value. Radiographic TLC was not significantly different from the helium dilution TLC.