泊松分布在消毒与灭菌效果监测法检出限中的应用

Role of poisson distribution in detection limit of examination of efficiency of disinfection and sterilization

目的用泊松分布的方法研究消毒技术规范中消毒与灭菌效果监测法的检出限,并用试验对其进行验证。方法用大肠埃希菌ATCC 25922、金黄色葡萄球菌ATCC 29213两种标准菌作为试验菌,配制一系列浓度的菌悬液,模拟消毒与灭菌效果监测法的操作过程,从某浓度菌悬液中取1ml倾注培养,连续100次,计数能检出细菌的试验次数,与公式计算的理论次数进行卡方检验比较,验证理论计算值与试验值是否存在差异有统计学意义。结果计算值与试验值两种菌株差异均无统计学意义;当从某一菌悬液中取1ml进注培养,要求细菌检出率在99.00%、95.00%、90.00%、60.00%、50.00%时,其菌悬液的浓度要求分别为4.61、3.00、2.30、0.92、0.69CFU/ml。结论在消毒效果监测过程中,对于采样后得到的混合溶液只能进行部分接种时,其不同检出率下的检出限可以用泊松分布的公式P(0)=e-λ进行计算,对于灭菌要求的监测,当细菌量很少时,将出现漏检,建议对其方法进行改进。

OBJECTIVE To use the poisson distribution to investigate the detection limit of examination of the efficiency of disinfection and sterilization and to perform the experiment to verify.METHODS Two types of standard bacteria,ATCC25922 and ATCC29213,were suspended in different concentrations and were under the experimental conditions to mimic the process of examination of sterilization and disinfection.At each concentration,1 mL bacteria suspension was cultured for 100 times.The number of plates containing bacteria was counted and compared with the number calculated from the equation through Chi-square test to see whether there was a difference between two groups.RESULTS For the two strands,the differences between their calculated values and their experimental values were both statistically insignificant.On pour-plate cultures using 1mL-aliquot of each bacterial suspension,the corresponding required suspension concentration for achieving a detection rate of 99.00%,95.00%,90.00%,60.00% and 50.00% was 4.61,3.00,2.30,0.92 and 0.69 CFU/mL,respectively.CONCLUSION In the examination of the efficiency of disinfection,for partially plating the sample suspension,the detection limit under different positive rate can be calculated according to poisson distribution equation P（0）=e-λ.However,for testing the sterilization when the number of bacteria is small,this method remains to be improved.