Growth of pathogenic Yersinia enterocolitica strains in minced meat with and without protective gas with consideration of the competitive background flora.

The growth of two pathogenic Yersinia enterocolitica strains (O:3, O:9 at 1 degree C, 4 degrees C, 10 degrees C and 15 degrees C) in minced meat produced under sterile conditions and in minced meat with a normal background flora was investigated. In addition, the influence of treatment with a protective gas (20% CO2, 80% O2) was tested. In minced meat produced under sterile conditions and incubated under normal atmospheric conditions, Y. enterocolitica increased in numbers by only 1 log at 1 degree C and 3.5 logs at 4 degrees C within 14 days. At 10 and 15 degrees C, there was about a 5-log increase in cell numbers within 5 days. There was a marked inhibition of growth by the background flora on Y. enterocolitica. This effect was so marked that only a slight additional inhibition on the growth of Y. enterocolitica at 1, 4 and 10 degrees C was observed under the CO2:O2 modified atmosphere. This is in contrast to the situation where minced meat with a low total bacterial count was used, and the growth of Y. enterocolitica was adversely affected by the CO2:O2 environment. The significance of raw minced meat in the development of human Y. enterocolitica infections is also discussed.