Elimination of Salmonella in Poultry with Ionizing Radiation

The radiation resistance of S. typhimurium in comminuted chicken meat was not affected by the breed of poultry (three different breeds tested) or by the type of meat (white or dark). A factor which did influence radio-resistance was the temperature during irradiation. A difference in radio-resistance was noted among five Salmonella serotypes tested. S.oranienburg was the most resistant and S.newport was the least resistant whereas S. thompson, S.heidelberg and S. typhimurium were intermediate. Of the salmonellae which survived irradiation in the non-frozen state, only an insignificant number were inactivated during subsequent quick-freezing and the concentration remained relatively constant over a three-month storage period at 0°F, Thus, salmonellae that have been irradiated (in chicken meat) do not appear to be any more susceptible to freezing injury compared with non-irradiated salmonellae. The psychrophiles in comminuted whole chicken meat surviving irradiation (300 krad) were a mixture of yeasts and members of the Achromobacter-Alicaligenes group. In quantitating salmonellae surviving irradiation in chicken meat by the plate count method, the greatest recovery was obtained with tryptic soy yeast extract agar. Selective media such as brilliant-green sulphadiazene agar, bismuth sulphite agar and MacConkey agar gave good recovery, but with Salmonella- Shigella agar or desoxycholate citrate agar results were poor. Recovery on brilliant green-sulphadiazene agar was enhanced by the addition of yeast extract. Enumeration of salmonellae in irradiated chicken by the ''most probable numbers'' method was comparable with results obtained by plate count. Satisfactory results were obtained with selenite cystine broth. Pre-enrichment into various nutrient broths before inoculation into a selective broth medium did not appear to enhance recovery. Repeated irradiation and sub-culturing of survivors produced a population of Salmonella with increased radio-resistance. Cells in the stationary phase of growth (24 h) were more radio-resistant than cells in the logarithmic phase (7 h). The growth rate of the radio-resistant cells at 98.6°F (37°C) did not differ from that of the parent strain. (author)