RESUMO
Shell eggs were immersed in bacterial suspensions containing 106 Yersinia enterocolitica /ml and subjected to either a temperature differential or a pressure differential inoculation technique in the presence or absence of 20 ppm iron to determine if Y. enterocolitica could penetrate and infect shell eggs. No Y. enterocolitica was detected inside eggs immediately after inoculation. After 3 d of storage at 10°C, Y. enterocolitica was detected in only one egg out of 24. After 7 d of storage at 10°C, approximately 14% of eggs from bacterial suspensions with no iron supplementation contained Y. enterocolitica . After 14 d, Yersinia counts exceeded log 6.0 CFU/ml and Yersinia were found inside 100% of eggs examined.
RESUMO
Experiments were undertaken to determine the growth characteristics of five strains of Yersinia enterocolitica in pasteurized milk at 4°C. Pasteurized milk was inoculated with approximately 10 or 1000 cells/ml of Y. enterocolitica , and was incubated at 4°C for 0, 3, 7, 14 and 21 d. Each sample was spread-plated in duplicate on Tryptone Soya Agar, MacConkey Agar and Cefsulodin-Irgasan-Novobiocin (CIN) agar. Plates were incubated at 25°C for 48 h or at 32°C for 24 h and enumerated for total and Yersinia plate count. All five strains of Y. enterocolitica competed very well with background microflora of pasteurized milk and reached levels of log 5.0 to 7.0/ml after 7 d at 4°C. Level of inoculation had little or no effect on the total number of Y. enterocolitica after 14 or 21 d in pasteurized milk at 4°C. Generation times at 4°C were highly strain-dependent.
