Sterilization of Escherichia coli O157:H7 Contaminated Beef by Gamma Irradiation

Escherichia coli O157:H7을 오염시킨 우육의 감마선 조사에 의한 살균효과

The gamma-radiation sensitivity of four kinds of Escherichia coli O157:H7 was investigated in frozen cells $(-18^{\circ}C)$ with 0.1 M phosphate buffer and inoculated cells in beef. The maximum populations were observed at 12 hr when E. coli O157:H7 was incubated in the tryptic soy broth at $37^{\circ}C$. In the case of the frozen cells at logarithmic phase, the $D_{10}$ and $12D_{10}$ values of four kinds of E. coli O157:H7 were $0.09{\sim}0.15\;kGy$ and $1.08{\sim}1.80\;kGy$, and inactivation factors were $13.33{\sim}22.22$ and $20.00{\sim}33.33$ at radiation doses of 2 and 3 kGy, respectively. The radiosensitivity of inoculated E. coli O157:H7 in beef showed the $D_{10}$ value of $0.30{\sim}0.47\;kGy$, the $12D_{10}$ value of $3.60{\sim}5.64\;kGy$, and inactivation factor of $4.26{\sim}10.00$. The radiosensitivity of the frozen cells was higher than that of the inoculated E. coli O157:H7 in beef. Gamma irradiation at doses within the range of 1.5 to 3 kGy is considered to be an effective method to control E. coli O157:H7 in beef.

4종류의 Escherichia coli O157:H7을 tryptic soy broth에 배양한 후 0.1 M phosphate buffer에 동결시킨 균체와 우육에 접종한 균체의 감마선 조사에 의한 방사선 감수성을 조사하였다. 균체의 증식은 tryptic soy broth에서 $37^{\circ}C$ 배양으로 24시간대에 최대균수를 나타내었다. 대수기때의 동결균체의 $D_{10}$ 값은 $0.09{\sim}0.15\;kGy$, $12D_{10}$값은 $1.08{\sim}1.80\;kGy$, 2와 3 kGy에서 불활성화 계수는 $13.33{\sim}33.33$이었다. 한편, 우육에 접종한 균체의 $D_{10}$값은 $0.30{\sim}0.47\;kGy$, $12D_{10}$값은 $3.60{\sim}5.64\;kGy$, 2와 3 kGy 선량에서의 불활성화계수는 $4.26{\sim}10.00$으로 동결균체가 우육접종균체보다 더 높은 방사선 감수성을 나타내었다.