Strantz A A, Zottola E A
Department of Food Science and Nutrition, University of Minnesota, 1334 Eckles, Avenue St. Paul 55108.
J Food Prot. 1989 Oct;52(10):712-714. doi: 10.4315/0362-028X-52.10.712.
A plating technique that would allow for recovery and enumeration of stressed Salmonella typhimurium was developed. The strain of S. typhimurium used in this study was isolated from an outbreak of salmonellosis caused by the consumption of contaminated pasteurized milk. Cultures propagated for 18 h at 37°C in Tryptic Soy Broth (TSB) were enumerated on Brilliant Green Agar (BGA), Salmonella-Shigella agar (SS), Xylose Lysine Desoxycholate Agar (XLD), and Hektoen Enteric Agar (HE). Recovery of 10 to 10 fewer cells was seen on the selective agars as compared to recovery on Tryptic Soy Agar (TSA). When the culture was spread plated onto TSA, allowed to stand at room temperature for 4 h, overlaid with XLD, HE, or SS, and incubated at 37°C for 24 h, recovery levels were comparable to recovery on TSA. Enhanced recovery of S. typhimurium cells that had been injured by freezing in TSB or in blended whole egg, or by heating at 54°C was also seen. In some cases recovery was at a higher level when the overlay procedure was used than on control TSA plates. Recovery of S. typhimurium from cheese that had been artificially contaminated with S. typhimurium , Staphylococcus aureus , and Pseudomonas fragi exceed control MPN values when the overlay procedure was used, although the recovery rate was within the MPN 95% confidence limits. The selective and differential properties of XLD, HE, and SS were maintained. Salmonella colonies appeared black, while the starter culture bacteria, S. aureus and P. fragi appeared as pinpoint white colonies. The potential exists for this procedure to be used for the direct enumeration of sublethally stressed salmonellae if their numbers exceed 100 per gram.
开发了一种可用于复苏和计数受胁迫鼠伤寒沙门氏菌的平板接种技术。本研究中使用的鼠伤寒沙门氏菌菌株是从因食用受污染巴氏杀菌牛奶引发的沙门氏菌病暴发中分离出来的。在胰蛋白胨大豆肉汤（TSB）中于37°C培养18小时的培养物，在亮绿琼脂（BGA）、沙门氏菌-志贺氏菌琼脂（SS）、木糖赖氨酸脱氧胆酸盐琼脂（XLD）和赫氏肠道琼脂（HE）上进行计数。与在胰蛋白胨大豆琼脂（TSA）上的复苏情况相比，在选择性琼脂上观察到复苏的细胞数量减少了10至10倍。当将培养物涂布在TSA上，在室温下放置4小时，覆盖上XLD、HE或SS，并在37°C下孵育24小时时，复苏水平与在TSA上的复苏水平相当。还观察到在TSB或全蛋液中冷冻或在54°C加热而受损的鼠伤寒沙门氏菌细胞的复苏得到增强。在某些情况下，使用覆盖程序时的复苏水平高于对照TSA平板。当使用覆盖程序时，从人工污染了鼠伤寒沙门氏菌、金黄色葡萄球菌和脆弱假单胞菌的奶酪中复苏的鼠伤寒沙门氏菌超过了对照MPN值，尽管回收率在MPN 95%置信限内。XLD、HE和SS的选择性和鉴别特性得以保持。沙门氏菌菌落呈黑色，而起始培养细菌金黄色葡萄球菌和脆弱假单胞菌呈针尖状白色菌落。如果每克亚致死胁迫沙门氏菌的数量超过100个，该程序有可能用于直接计数。
