Laboratory of Food Microbiology, Department of Nutrition, Health Sciences Center, Federal University of Paraíba, João Pessoa, Brazil.
Laboratory of Culture and Cell Analysis, Technical School of Health, Health Sciences Center, Federal University of Paraíba, João Pessoa, Brazil.
Food Microbiol. 2019 Dec;84:103240. doi: 10.1016/j.fm.2019.103240. Epub 2019 Jun 10.
This study evaluated whether the pre-exposure (24, 48 and 72 h) to sublethal conditions caused by acetic acid (AA), lactic acid (LA), sodium chloride (NaCl) or potassium chloride (KCl) could induce increased cross-tolerance to the essential oils from Origanum vulgare L. (OVEO) and Rosmarinus officinalis L. (ROEO) in different Listeria monocytogenes strains. Damage to membrane integrity, membrane potential, enzymatic activity and efflux activity in L. monocytogenes cells pre-exposed (24 h) to AA or NaCl and further treated with OVEO or ROEO (8 and 24 h) were investigated using flow cytometry (FC). Results of minimum inhibitory concentration (MIC) modulation test showed that pre-exposure to sublethal conditions caused by organic acids or salts increased cross-tolerance only to ROEO, since MIC of ROEO increased up to 4.8-fold against pre-exposed cells. Otherwise, MIC of OVEO against these pre-exposed cells was up to ten-fold lower than that observed against not pre-exposed cells, indicating no increase in cross-tolerance. Bacterial survival assays showed that ROEO only decreased the counts over time of cells not pre-exposed to organic acids or salts, while OVEO decreased similarly or more the counts of pre-exposed cells compared to not pre-exposed cells. Results of FC analysis showed that all measured functions in L. monocytogenes cells pre-exposed to AA or NaCl and treated with OVEO or ROEO were affected, although with different intensities. These data indicate that exposure to sublethal conditions imposed by organic acids or salts could result in a phenotype of increased cross-tolerance to ROEO but not to OVEO in L. monocytogenes.
本研究评估了在亚致死条件下（24、48 和 72 小时）暴露于乙酸（AA）、乳酸（LA）、氯化钠（NaCl）或氯化钾（KCl）是否会导致不同李斯特菌菌株对牛至精油（OVEO）和迷迭香精油（ROEO）的交叉耐受增加。使用流式细胞术（FC）研究了预先暴露（24 小时）于 AA 或 NaCl 的单核细胞增生李斯特菌细胞的膜完整性、膜电位、酶活性和外排活性的损伤，然后用 OVEO 或 ROEO （8 和 24 小时）处理。最低抑菌浓度（MIC）调制试验结果表明，有机酸或盐引起的亚致死条件的预先暴露仅增加了对 ROEO 的交叉耐受，因为 ROEO 的 MIC 对预先暴露的细胞增加了 4.8 倍。然而，OVEO 对这些预先暴露的细胞的 MIC 比未预先暴露的细胞低了十倍，表明没有增加交叉耐受。细菌存活试验表明，ROEO 仅随着时间的推移减少了未预先暴露于有机酸或盐的细胞的数量，而 OVEO 则与未预先暴露的细胞相比，对预先暴露的细胞的数量减少了相同或更多。FC 分析结果表明，预先暴露于 AA 或 NaCl 并用 OVEO 或 ROEO 处理的单核细胞增生李斯特菌细胞的所有测量功能均受到影响，尽管强度不同。这些数据表明，在有机酸或盐施加的亚致死条件下暴露可能导致李斯特菌对 ROEO 的交叉耐受增加的表型，但对 OVEO 则没有。
