Salazar Joelle K, Tesfaldet Bereket, Zamperlini Michelle, Streufert Rachel, Fay Megan, Keller Susanne E
U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition, 6502 South Archer Road, Bedford Park, Illinois 60501; and.
U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition, 5001 Campus Drive, College Park, Maryland 20740, USA.
J Food Prot. 2022 Mar 1;85(3):398-405. doi: 10.4315/JFP-21-320.
Salmonella enterica is well known for its ability to survive and persist in low-moisture environments. Previous studies have indicated a link between the initial cell level and the population of Salmonella that survives after desiccation and subsequent storage; however, how the initial cell concentration affects survival is unknown. This study was conducted to examine this phenomenon and to determine whether it occurs in other microorganisms, specifically Shiga toxigenic Escherichia coli (STEC) and Enterococcus faecium. Salmonella, STEC, and E. faecium were grown as sessile cells on Trypticase soy agar with yeast extract (TSAYE) and harvested in buffered peptone water (BPW). To determine recovery at different initial cell levels, cultures were diluted to 9, 7, and 5 log CFU/mL and applied to filters. Filters were dried for 24 h and then stored for 28 days at 25°C and 33% relative humidity. During storage, cells were recovered from filters with BPW and cultivated on TSAYE. Recovery of both Salmonella and E. coli, but not E. faecium, was nonproportional. Lower initial populations were less viable after 24 h of desiccation; ≥10 log CFU/mL was recovered when 11 log CFU/mL was desiccated, but <3 log CFU/mL was recovered when 5 log CFU/mL was desiccated. Once dried, persistence did not appear affected by initial cell concentration. When inactivated (heat-treated) cells were added to the diluent, recovery of Salmonella was proportional with respect to the initial cell level. To further examine the response to desiccation, Salmonella was diluted in BPW containing 1 of 11 test cell components related to quorum sensing or known to affect desiccation resistance to assess recovery and persistence. Of the 11 additions, only cell debris fractions, cell-free extract, and peptidoglycan improved recovery of Salmonella. Desiccation survival appears related to cell wall components; however, the exact mechanism affecting survival remains unknown.
肠炎沙门氏菌以其在低水分环境中生存和持续存在的能力而闻名。先前的研究表明初始细胞水平与干燥及后续储存后存活的沙门氏菌数量之间存在联系；然而，初始细胞浓度如何影响存活率尚不清楚。进行本研究以检查这一现象，并确定其是否在其他微生物中发生，特别是产志贺毒素大肠杆菌（STEC）和粪肠球菌。将沙门氏菌、STEC和粪肠球菌作为固着细胞在含有酵母提取物的胰蛋白胨大豆琼脂（TSAYE）上培养，并在缓冲蛋白胨水（BPW）中收获。为了确定不同初始细胞水平下的回收率，将培养物稀释至9、7和5 log CFU/mL并施加到滤膜上。滤膜干燥24小时，然后在25°C和33%相对湿度下储存28天。在储存期间，用BPW从滤膜上回收细胞，并在TSAYE上培养。沙门氏菌和大肠杆菌的回收率不成比例，但粪肠球菌的回收率成比例。较低的初始菌量在干燥24小时后存活率较低；当干燥11 log CFU/mL时回收量≥10 log CFU/mL，但当干燥5 log CFU/mL时回收量<3 log CFU/mL。一旦干燥，持久性似乎不受初始细胞浓度的影响。当将灭活（热处理）细胞添加到稀释剂中时，沙门氏菌的回收率与初始细胞水平成比例。为了进一步检查对干燥的反应，将沙门氏菌在含有与群体感应相关或已知影响抗干燥性的11种测试细胞成分之一的BPW中稀释，以评估回收率和持久性。在11种添加物中，只有细胞碎片部分、无细胞提取物和肽聚糖提高了沙门氏菌的回收率。干燥存活率似乎与细胞壁成分有关；然而，影响存活的具体机制仍然未知。
