Zúñiga-Estrada A, López-Merino A, de la Garza L M
Departamento de Microbiología, Instituto Politécnico Nacional, Mexico.
Rev Latinoam Microbiol. 1995 Jul-Sep;37(3):257-65.
The purpose of this research was to determine the survival of Listeria monocytogenes in sterile skim milk during the fermentation with a yogurt starter culture and during storage at refrigeration temperature. Sterile skim milk was inoculated with 10(3), 10(5) and 10(7) cfu/ml of L. monocytogenes and with 10(6) cfu of lactic acid bacteria. Inoculated milks were fermented for 8 h at 42 degrees C, followed by refrigeration at 4 degrees C. Samples were taken at 2 h intervals during fermentation and at 2 days intervals during storage. Acidity and pH were measured, as well as viable count of lactic acid bacteria and pathogen. L. monocytogenes survived 8h, 10 days and 32 days in the fermented milk, when the inocula were 10(3), 10(5) and 10(7) cfu/ml, respectively. Inhibition of the pathogen was associated with a decrease of pH below 4.0 and increase in acidity. It was demonstrated that this pathogen is able to survive several weeks in milk fermented with a starter culture, contrary to the general belief which considered it very difficult due to the low pH. Therefore fermented milks may play an important role in the transmission of these bacteria.
本研究的目的是确定在酸奶发酵剂发酵过程中以及冷藏温度储存期间，单核细胞增生李斯特菌在无菌脱脂乳中的存活情况。向无菌脱脂乳中接种每毫升10³、10⁵和10⁷ 个菌落形成单位（cfu）的单核细胞增生李斯特菌以及10⁶ cfu的乳酸菌。接种后的牛奶在42℃下发酵8小时，随后在4℃下冷藏。在发酵期间每隔2小时取样，在储存期间每隔2天取样。测量酸度和pH值，以及乳酸菌和病原体的活菌数。当接种量分别为每毫升10³、10⁵和10⁷ cfu时，单核细胞增生李斯特菌在发酵乳中分别存活8小时、10天和32天。病原体的抑制与pH值降至4.0以下和酸度增加有关。结果表明，与普遍认为由于低pH值该病原体很难存活的观点相反，这种病原体能够在发酵剂发酵的牛奶中存活数周。因此，发酵乳可能在这些细菌的传播中起重要作用。
