Studies on the Irradiation of Microorganisms in Relation to Food Preservation: I. The Comparative Sensitivities of Specific Bacteria of Public Health Significance

Abstract

The limits of tolerance to gamma irradiation have been determined for 21 cultures representative of the following bacterial species of public health significance in foods: Staphylococcus aureus, Escherichia coli (types I and II), Aerobacler aerogenes, A. cloacae, Streptococcus faecalis, Salmonella gallinarum, S. tennessee, Mycobacterium tuberculosis, Clostridium botulinum (types A and E). A several-fold difference in radiation sensitivity has been demonstrated, specific sensitivity being influenced by the nature of the suspending medium during irradiation.Spores of C. botulinum, type A, were more resistant than those of type E, while six strains of staphylococci of differing phage pattern showed closely similar tolerances. The most sensitive species among those tested was M. tuberculosis. The coliform organisms were more sensitive than the salmonellae, which, in turn, were more sensitive than the staphylococci and S. faecalis. Destruction of coliform bacteria in irradiated foods cannot, therefore, be used as an index of adequate pasteurization.Staphylococcal emetic toxin present in pork sausage and suspended in culture filtrates was destroyed by irradiation at comparatively low levels in contradistinction to the findings for the toxin of C. botulinum.

Gamma Ray Processing to Destroy Staphylococcus aureus in Mechanically Deboned Chicken Meat

“…This appeared questionable as such results were not compatible with the results we obtained with S. aureus ATCC 13565. Further, Erdman et al (1961) and Tiwari and Maxcy (1972) reported D-values for S. aweus in broth that were significantly higher than those we obtained in MDCM. The resistance (D-value = 0.36 kGy) of stationary phase S. aureus ATCC 13565 to gamma radiation when mixed with MDCM was lower than most serovars of Salmonella reported by Thayer et al (1990).…”

“…Enterotoxin was found only in the non-irradiated samples that were subjected to abuse for 20 hr at 35°C (Table 2). DISCUSSION ERDMAN et al (1961) reported that the strains of 5. uureu.s they examined had greater resistance to gamma radiation than did salmonellae. This appeared questionable as such results were not compatible with the results we obtained with S. aureus ATCC 13565.…”

“…Published information on the effects of gamma radiation on staphylococci, particularly in meat, is very limited. Erdman et al (1961) studied the radiation resistance of 6 strains of 24 hr cultures of S. aureu.r to gamma radiation when suspended in broth and of one strain suspended in chopped beef. Samples were irradiated at "room" temperature using a cobalt60 source with a dose rate of 0.05 kGy/min.…”

“…They did not report Dvalues; however, a D-value could be extrapolated from the published regression curve for the destruction of S. aureuS in broth, which we estimated to be 0.52 kGy. Erdman et al (1961) reported that Stup~yZococcu.s was more radiation resistant than salmonellae, and that cells incorporated into chopped beef were significantly more resistant than those suspended in broth. Tiwari and Maxcy (1972) reported a D-value for stationary phase cells of S. aweus of 0.43 kGy when irradiated in nutrient broth.…”

Effect of Irradiation Temperature on Inactivation of Clostridium botulinum Toxin Type E by Gamma Rays

“…The radiation inactivation of Clostridium botulinum toxin has been studied and has been found to be radioresistant. Erdman, Thatcher & MacQueen (1961) reported that there was no effect on the activity of type A toxin in pork sausage or broth at irradiation doses up to 2.2 x lo6 rep. Wagennaar & Dack (1960) noted that the inactivation dose for the toxin depended upon the substrate, cheese affording greater protection than did Trypticase broth or phosphate buffer. Type E toxin was also found to be radioresistant and Skulberg (1965) reported the decimal reduction dose (Dlo value) as 2.1 Mrad.…”