Zhao T, Doyle M P, Zhao P, Blake P, Wu F M
Center for Food Safety, University of Georgia, Griffin 30223-1797, USA.
J Food Prot. 2001 Oct;64(10):1607-9. doi: 10.4315/0362-028x-64.10.1607.
Six human isolates of Escherichia coli O157:H7 and E. coli (ATCC 11229) were used to determine the concentrations of free chlorine and exposure times required for inactivation. Free chlorine concentrations of 0.25, 0.5, 1.0, and 2.0 ppm at 23 degrees C were evaluated, with sampling times at 0, 0.5, 1.0, and 2.0 min. Results revealed that five of six E. coli O157:H7 isolates and the E. coli control strain were highly susceptible to chlorine, with >7 log10 CFU/ml reduction of each of these strains by 0.25 ppm free chlorine within 1 min. However, comparatively, one of the seven strains was unusually tolerant to chlorine at 23 degrees C for 1 min, with a 4-, 5.5-, 5.8-, and >5.8-log CFU/ml reduction at free chlorine concentrations (ppm) of 0.25, 0.5, 1.0, and 2.0. respectively. Based on these studies most isolates of E. coli O157:H7 have no unusual tolerance to chlorine; however, one strain was exceptional in being recovered after 1-min of exposure of 10(7) CFU/ml to 2.0 ppm of free chlorine. This isolate may be a useful reference strain for future studies on chlorine tolerance of E. coli O157:H7.
使用6株人源大肠杆菌O157:H7分离株和大肠杆菌（美国典型培养物保藏中心11229）来确定灭活所需的游离氯浓度和暴露时间。在23摄氏度下评估了游离氯浓度为0.25、0.5、1.0和2.0 ppm的情况，采样时间为0、0.5、1.0和2.0分钟。结果显示，6株大肠杆菌O157:H7分离株中的5株以及大肠杆菌对照菌株对氯高度敏感，在1分钟内，0.25 ppm的游离氯可使这些菌株中的每一株减少>7 log10 CFU/ml。然而，相比之下，7株菌株中的1株在23摄氏度下对氯异常耐受1分钟，在游离氯浓度（ppm）为0.25、0.5、1.0和2.0时，分别减少4、5.5、5.8和>5.8 log CFU/ml。基于这些研究，大多数大肠杆菌O157:H7分离株对氯没有异常耐受性；然而，有一株菌株在10(7) CFU/ml暴露于2.0 ppm游离氯1分钟后仍能被回收，这是个例外。该分离株可能是未来大肠杆菌O157:H7耐氯性研究的有用参考菌株。
