Departamento de Higiene y Tecnología de los Alimentos, Facultad de Veterinaria, Universidad de León, 24071 León, Spain.
Int J Food Microbiol. 2010 Jan 1;136(3):278-82. doi: 10.1016/j.ijfoodmicro.2009.09.024. Epub 2009 Oct 4.
Salmonella Typhimurium CECT 443 inactivation at pH 2.5 in Mineral Medium (MM) and MM supplemented with 0.01% (w/v) arginine, lysine or glutamic acid was studied using stationary-phase cells grown in buffered BHI pH 7.0 (non-acid adapted cells) and acidified BHI up to pH 4.5 with acetic, citric, lactic and hydrochloric acids (acid adapted cells). In all cases, acid adapted cells, with D-values ranging from 23.34 to 86.90 min, showed a significantly higher acid resistance than non-acid adapted cells, with D-values between 8.90 and 10.29 min. Whereas the conditions used for acid adaptation did not exert a significant effect on the acid resistance of the S. Typhimurium CECT 443 resulting cells, the inclusion of lysine and arginine in the challenge medium protected them against acid inactivation, reaching D-values of about 2 and 3 times higher, respectively, than those found in MM or MM supplemented with glutamic acid. None of these three amino acids significantly modified the acid resistance of non-acid adapted cells. The relative expression level of adiA (encoding the arginine decarboxylase), adiY (encoding the transcriptional activator of adiA), cadA (encoding the lysine decarboxylase) and cadB (encoding the lysine/cadaverine transport protein) was examined by quantitative PCR. Acid adapted cells showed higher relative expression levels for both systems, arginine decarboxylase and lysine decarboxylase, which demonstrates that the induction of specialized pH-homeostatic systems plays an important role in S. Typhimurium CECT 443 protection against acid stress. However, the increased acid resistance showed by acid adapted cells challenged in MM arginine or lysine free suggests the existence of other microbial survival strategies.
在 pH 值为 2.5 的矿物培养基（MM）和补充有 0.01%（w/v）精氨酸、赖氨酸或谷氨酸的 MM 中研究了肠炎沙门氏菌 CECT443 的失活动力学，使用缓冲 BHI pH 值为 7.0（未适应酸性的细胞）和用乙酸、柠檬酸、乳酸和盐酸酸化至 pH 值 4.5 的 BHI（适应酸性的细胞）培养的静止期细胞。在所有情况下，D 值范围为 23.34 至 86.90 分钟的适应酸性细胞表现出比 D 值在 8.90 至 10.29 分钟之间的未适应酸性细胞更高的耐酸性。虽然用于酸性适应的条件对肠炎沙门氏菌 CECT443 产生的细胞的耐酸性没有显著影响，但在挑战培养基中添加赖氨酸和精氨酸可以保护它们免受酸失活，分别达到约 2 和 3 倍的 D 值高于在 MM 或补充有谷氨酸的 MM 中发现的值。这三种氨基酸都没有显著改变未适应酸性细胞的耐酸性。通过定量 PCR 检查 adiA（编码精氨酸脱羧酶）、adiY（编码 adiA 的转录激活子）、cadA（编码赖氨酸脱羧酶）和 cadB（编码赖氨酸/尸胺转运蛋白）的相对表达水平。适应酸性的细胞显示出两个系统（精氨酸脱羧酶和赖氨酸脱羧酶）的相对表达水平更高，这表明专门的 pH 稳态系统的诱导在肠炎沙门氏菌 CECT443 对酸应激的保护中起着重要作用。然而，在 MM 中缺乏精氨酸或赖氨酸的适应酸性细胞受到挑战时表现出的增加的耐酸性表明存在其他微生物生存策略。
