A collection of 23 Listeria monocytogenes strains of clinical and food origin was tested for their ability to recover and grow out in half Fraser enrichment broth following the ISO 11290-1:2017 protocol. Recovery of sub-lethally heat-injured cells in half Fraser broth was compared to reference cells with no stress pre-treatment. The enrichments were followed over time by plate counts and the growth parameters were estimated with the 3-phase model which described the data best. The reference cells without stress pre-treatment showed a short lag duration, which ranged from 1.4 to 2.7 h. However, significant variation in the ability to recover after 60 °C heat stress was observed among the tested strains and resulted in a lag duration from 4.7 to 15.8 h. A subset of strains was also exposed to low-temperature acid stress, and the lag duration showed to be also stress dependent. Scenario analyses and Monte Carlo simulations were carried out using the growth parameters obtained in the enrichments. This demonstrated that when starting with one cell, the detection threshold for efficient transfer of at least one cell to the secondary enrichment step, i.e. 2 log₁₀ CFU/ml, was not reached by 11 of 23 strains tested (48%) after exposure to 60 °C heat stress. Increasing the incubation time from 24 to 26 h and the transfer volume from 0.1 to 1.0 ml can increase the average probability to transfer at least one cell to the secondary enrichment step from 79.9% to 99.0%. When optimizing enrichment procedures, it is crucial to take strain variability into account as this can have a significant impact on the detection efficacy.

收集23种李斯特菌按照ISO 11290-1：2017协议测试了临床和食品来源的菌株在一半Fraser浓缩肉汤中恢复和生长的能力。将一半Fraser肉汤中亚致死热损伤细胞的恢复与未进行压力预处理的参考细胞进行了比较。随着时间的流逝，富集后进行平板计数，并用描述数据最好的3相模型估算生长参数。未进行应力预处理的参比细胞显示出较短的滞后时间，范围为1.4至2.7 h。但是，在测试菌株中观察到60°C热应力后恢复能力的显着变化，导致滞后时间为4.7至15.8 h。一部分菌株也暴露于低温酸胁迫下，并且滞后时间也显示出与胁迫有关。使用在富集中获得的生长参数进行了方案分析和蒙特卡洛模拟。这表明，从一个细胞开始，有效转移至少一个细胞到第二次富集步骤的检测阈值即2 log暴露于60°C热应激后，测试的23个菌株中有11个（48％）未达到₁₀ CFU / ml。将孵育时间从24小时增加到26小时，转移量从0.1毫升增加到1.0毫升，可以将将至少一个细胞转移到二级富集步骤的平均概率从79.9％增加到99.0％。在优化富集程序时，至关重要的是要考虑到菌株变异性，因为这会对检测效率产生重大影响。