Toxicity of Spores of Clostridium botulinum Strain 33 A in Irradiated Ground Beef

Abstract

(4-5 Mrad.) do not completely inactivate spore toxin or enzymes. The present study concerns spore toxin during and after irradiation of 4 x I O~ spores of Clostridium botulinum per g. of canned ground beef irradiated to 4-5 Mrad., at temperatures of -25", 0" and +25". During subsequent incubation of irradiated samples at 30" for 10 months, periodic analyses showed no viable spores. Toxin was tested on (i) non-homogenized samples and (ii) samples homogenized in a tissue grinder.In samples irradiated at -25" and 0" and in un-irradiated un-incubated controls, 4 minimal lethal doses (m.1.d.) of toxin were found in non-homogenized samples immediately after irradiation. The toxin titre of irradiated samples gradually diminished to approximately half of its initial value at the end of 10 months at 30". In identical sets of homogenized irradiated samples, 8 m.1.d. were found initially and the titre increased to 44m.l.d. after 2 weeks to 4 months of incubation at 30". Thereafter, the toxin titre slowly deteriorated to approximately 25 m.1.d. at the end of 10 months.Samples irradiated at 25" exhibited a definite increase in toxin titre even immediately after irradiation. This seems to suggest the possibility of new toxin synthesis either during or after radiation. The toxin titre in homogenized samples reached 64 m.1.d. after 2 months at 30" and thereafter slowly diminished to 31 m.1.d. at 10 months.Toxin titres in radiation-damaged spores were small in comparison to un-irradiated C. botulinum growing in beef which reached 1000 to 5000 m.1.d. in 2 days at 30°.

Physical Treatments to Control Clostridium botulinum Hazards in Food

“…This might be the reason that the aforementioned studies have reported the presence of BoNT in gamma-sterilized food [ 91 , 91 , 107 , 108 , 109 ]. Fernandez et al [ 110 ] studied the toxicity of strain 33A spores in canned ground beef irradiated to 45 kGy at temperatures of −25, 0, and 25 °C; they found small minimal lethal doses of toxin in the irradiated samples which could be due to (i) the germination of irradiated spores, (ii) slow lysis of spores at 25°, (iii) new toxin synthesis by those spore enzymes which remained active after irradiation, (iv) activation or fragmentation of pre-existing toxin molecules, etc. Meanwhile, the irradiation in combination with high temperatures (i.e., >40 °C) can synergistically inactivate the BoNT [ 17 ].…”