Department of Food and Animal Biotechnology, Center for Agricultural Biomaterials, and Research Institute for Agriculture and Life Sciences, Seoul National University, Seoul 151-921, Republic of Korea.
J Food Prot. 2012 Oct;75(10):1867-72. doi: 10.4315/0362-028X.JFP-11-512.
Selective agar is inadequate for supporting recovery of injured cells. During risk assessment of certain foods, both injured and noninjured cells must be enumerated. In this study, a new method (agar spray method) for recovering sublethally heat-injured microorganisms was developed and used for recovery of heat-injured Salmonella Typhimurium and Listeria monocytogenes. Molten selective agar was applied as an overlay to presolidified nonselective tryptic soy agar (TSA) by spray application. Heat-injured cells (55°C for 10 min in 0.1% peptone water or 55°C for 15 min in sterilized skim milk) were inoculated directly onto solidified TSA. After a 2-h incubation period for cell repair, selective agar was applied to the TSA surface with a sprayer, and the plates were incubated. The recovery rate for heat-injured Salmonella Typhimurium and L. monocytogenes with the spray method was compared with the corresponding rates associated with TSA alone, selective media alone, and the conventional overlay method (selective agar poured on top of resuscitated cells grown on TSA and incubated for 2 h). No significant differences (P > 0.05) were found in pathogen recovery obtained with TSA, the overlay method, and the spray method. However, a lower recovery rate (P < 0.05) was obtained for isolation of injured cells on selective media. Overall, these results indicate that the agar spray method is an acceptable alternative to the conventional overlay method and is a simpler and more convenient approach to recovery and detection of injured cells.
选择性琼脂不足以支持受损细胞的恢复。在某些食品的风险评估中，必须对受损细胞和未受损细胞进行计数。在这项研究中，开发了一种新的方法（琼脂喷雾法）来回收亚致死热损伤的微生物，并将其用于回收热损伤的鼠伤寒沙门氏菌和单核细胞增生李斯特菌。将熔融的选择性琼脂通过喷雾应用于预凝固的非选择性胰蛋白酶大豆琼脂（TSA）的覆盖层上。将热损伤细胞（在 0.1%蛋白胨水中 55°C 加热 10 分钟或在消毒的脱脂乳中 55°C 加热 15 分钟）直接接种到固体 TSA 上。在细胞修复的 2 小时孵育期后，用喷雾器将选择性琼脂应用于 TSA 表面，并孵育平板。用喷雾法回收热损伤的鼠伤寒沙门氏菌和单核细胞增生李斯特菌的回收率与 TSA 单独、选择性培养基单独和传统覆盖法（将选择性琼脂倒在 TSA 上生长的复苏细胞上，孵育 2 小时）的相应回收率进行了比较。用 TSA、覆盖法和喷雾法回收的病原体没有发现显著差异（P > 0.05）。然而，在选择性培养基上分离受损细胞的回收率较低（P < 0.05）。总的来说，这些结果表明，琼脂喷雾法是传统覆盖法的一种可接受的替代方法，是一种更简单、更方便的回收和检测受损细胞的方法。
