李斯特菌在浮游和固定生长条件下的适应性酸耐受反应。

Adaptive acid tolerance response of Listeria monocytogenes strains under planktonic and immobilized growth conditions.

机构信息

Center for Meat Safety & Quality, Department of Animal Sciences, 1171 Campus Delivery, Colorado State University, Fort Collins, CO 80523, USA.

出版信息

Int J Food Microbiol. 2012 Oct 1;159(2):160-6. doi: 10.1016/j.ijfoodmicro.2012.07.027. Epub 2012 Aug 3.

DOI:10.1016/j.ijfoodmicro.2012.07.027

PMID:22980026

Abstract

The acid resistance of Listeria monocytogenes was evaluated: (i) after short (shock) or long-term (adaptation during growth) exposure to reduced (5.5) or neutral (7.2) pH in a liquid (broth) medium or on a solid surface (agar), and (ii) after growth on the surface of ham and turkey slices or in homogenates of these products. Three L. monocytogenes strains (serotypes 1/2a, 1/2b and 4b) were individually inoculated at: (i) 10(4)-10(5)CFU/ml in tryptic soy broth with 0.6% yeast extract (TSBYE) or on tryptic soy agar with 0.6% yeast extract (TSAYE) at pH 7.2 with 1% (+G) or without (-G) glucose of or TSBYE and TSAYE with 0.25% glucose at pH 5.5 (lactic acid) and incubated at 20°C, and (ii) 10(2)-10(3)CFU/cm(2) on ham and turkey slices (pH 6.39-6.42; formulated with potassium lactate and sodium diacetate) or in their homogenates (1:4 and 1:9; representing viscous [slurry] and liquid residues [purge], respectively), and stored at 10°C. The acid resistance of each strain was assessed in TSBYE of pH 3.5 (lactic acid) for strains growing in broth or on agar surfaces, and in TSBYE of pH 1.5 (HCl) for strains growing on ham and turkey slices or in their homogenates. Habituation at pH 5.5 for 3 or 24h at 20°C increased acid (pH 3.5) resistance of all strains compared to the control (pH 7.2). Cells grown on the surface of TSAYE-G (pH 7.2 or 5.5) showed higher resistance than cells grown in broth (TSBYE-G), whereas the opposite was observed for cells grown on TSAYE + G or in TSBYE + G. Growth of L. monocytogenes on meat product slices was markedly slower than in homogenates. Pathogen reductions following exposure to pH 1.5, after 10 and 27days of storage were strain-dependent and in the ranges of 0.5-2.5, 1.3-4.5 and 4.0-7.6 log units for cells grown on product slices in 1:4 and 1:9 homogenates, respectively. The results suggest that L. monocytogenes cells growing on food surfaces or in viscous matrices may show higher resistance to lethal acid conditions than cells growing in liquid substrates.

摘要

评估了李斯特菌（Listeria monocytogenes）的耐酸能力：（i）在液体（肉汤）培养基或固体表面（琼脂）上经短期（冲击）或长期（生长过程中的适应）暴露于降低（5.5）或中性（7.2）pH 后，以及（ii）在火腿和火鸡切片表面生长或在这些产品的匀浆中生长后的耐酸能力。将 3 株李斯特菌（血清型 1/2a、1/2b 和 4b）分别以以下方式单独接种：（i）在胰蛋白酶大豆肉汤（含 0.6%酵母提取物）（TSBYE）或含 0.6%酵母提取物的胰蛋白酶大豆琼脂（TSAYE）中，pH 为 7.2，含 1%（+G）或不含（-G）葡萄糖，或含 0.25%葡萄糖的 TSBYE 和 TSAYE，在 20°C 下孵育，接种浓度为 10(4)-10(5)CFU/ml，或在 pH 5.5（乳酸）下接种浓度为 10(2)-10(3)CFU/cm(2)，在火腿和火鸡切片（pH 6.39-6.42；用乳酸钾和双乙酸钠配制）或其匀浆（1:4 和 1:9；分别代表粘性[糊状物]和液体残留[冲洗物]）上生长，并在 10°C 下储存。用 pH 3.5（乳酸）的 TSBYE 评估每种菌株在生长于肉汤或琼脂表面的菌株中的耐酸性，用 pH 1.5（HCl）的 TSBYE 评估在火腿和火鸡切片或其匀浆中生长的菌株的耐酸性。在 20°C 下于 pH 5.5 下适应 3 或 24h 可使所有菌株的耐酸能力（pH 3.5）比对照（pH 7.2）增加。在 pH 7.2 或 5.5 的 TSAYE-G 表面上生长的细胞比在肉汤（TSBYE-G）中生长的细胞具有更高的抗性，而在 pH 7.2 或 5.5 的 TSAYE + G 或 TSBYE + G 中生长的细胞则相反。李斯特菌在肉产品切片上的生长速度明显慢于在匀浆中的生长速度。在 10 和 27 天储存后暴露于 pH 1.5 时的病原体减少量因菌株而异，范围分别为在 1:4 和 1:9 匀浆中在产品切片上生长的细胞为 0.5-2.5、1.3-4.5 和 4.0-7.6 log 单位。结果表明，与在液体基质中生长的细胞相比，在食品表面或粘性基质中生长的李斯特菌细胞可能对致死酸条件具有更高的抗性。