A model system (chicken skins with chicken exudate) was used to determine if Clostridium botutinum type E (Beluga) spores, stressed by low dose irradiation, would develop and produce toxin at abuse temperatures of 10 and 30°C in the absence of characteristic spoilage. Unstressed spores germinated, multiplied, and produced toxin on vacuum-packed chicken skins, stored at either 30 or 10°C. Cell numbers increased faster and toxin was evident sooner at 3OoC than at 10°C. At 30°C, growth occurred and toxin was produced more slowly when samples were incubated aerobically than anaerobically. When samples were incubated aerobically at IO'C, no toxin was detected within a test period of 14 days. An irradiation dose of 0.3 Mrad at 5°C reduced a spore population on vacuumsealed chicken skins by about 90%. The surviving population produced toxin at 3OoC under either aerobic or anaerobic conditions, at 10°C no toxin was detected even on skins incubated anaerobically. Under the worst conditions (3OoC, vacuum packed) toxin was not detected prior to characteristic spoilage caused by the natural flora surviving 0.3 Mrad.

The effect of sodium phosphates with and without NaCl, on the ability of unstressed and heat-stressed Moraxella-Acinetobacter (M-A) isolate number 7 cells to form colonies in plate count agar (PCA) was determined. The effectiveness, in order of decreasing ability, of phosphates to inhibit colony formation of unstressed M-A cells was as follows: sodium tripolyphosphate (NasP,Oro; STPP), sodium pyrophosphate (Na4P207; SPP), and sodium orthophosphate (NajP04; SP). Filter sterilized STPP was more inhibitory than when heated and inhibition was not related to pH. Certain combinations of NaCl and STPP were additive whereas combinations of NaCl and SPP exhibited a synergistic effect. Heat-stressed M-A cells were more sensitive to levels of NaCl(O.8%) than to levels of STPP (0.1%) or SPP (0.12%); all shown to have no effect on the number of colonies formed in PCA by unstressed cells.

This p a p e r is concerned.with the kinetics of hemolysis of chicken red cells b y the simple hemolysins, saponin, sodium taurocholate, and sodium oleate. T h e action of these lysins has been extensively studied on m a m m a l i a n red cells, b u t quantitative investigations on the n u d eated cell are wanting.

The effect of irradiation (0.5, 1.0, 1.5 Mrad) on the microbiological safety and stability of temperature-abused (27"C, 60 days) bacon cured with, 1.5% NaCI, 0.25% sucrose, 0.3% NasP30ro, 0.055% Na-erythorbate, with or without NaN02 (40 p/g) was determined. Unioculated bacon (120 c(g NaNOz/g) had a sour odor within 13 days, and, if inoculated with ca. 2 C. botulinurn spores/g, 73% of the samples became toxic within 60 days. Irradiation with 0.5 Mrad prevented spoilage of uninoculated bacon by virtue of reducing the aerobic plate count to <1.0/g; irradiation with 1.0 Mrad sterilized bacon. Pouches of bacon, inoculated with C. botulinurn spores (2 spores/g), swelled and became toxic; development of swelling and toxicity was delayed by incorporation of NaN02 (40 pg/g) or by irradiation with 0.5 Ivlrad. Irradiation with 1.0 Mrad decreased the number of swollen and toxic pouches. Irradiation with 1.5 Mrad prevented swelling and toxicity of bacon inoculated with 2 spores/g.

The effect of various stages of the irradiation processing of beef on the injury and inactivation of radiation-resistant Moraxella-Acinetobactor cells was studied. Moraxella-Acinetobacter cells were more resistant to heat inactivation and injury when heated in meat with salts (0.75% NaCl and 0.375% sodium tripolyphosphate) then in meat without salts. These salts had no effect on radiation resistance. Both radiation- and heat-injured cells were unable to form colonies at 30 degrees C in plate count agar containing 0.8% NaCl. Neither unstressed nor heat-stressed cells were able to multiply in minced beef incubated at 30 degrees C for 12 h. Only after the beef was diluted 1:10 with peptone water were the heat-injured cells able to repair and eventually multiply. Heated cells were more sensitive to radiation inactivation and injury than unheated cells. After repair, the cells regained their resistance to both NaCl and irradiation. Freezing and storage at -40 degrees C for 14 days had only a slight effect on either unstressed or heat-stressed cells.