Division of Food Processing Science and Technology, U.S. Food and Drug Administration, 6502 South Archer Road, Bedford Park, Illinois 60501, USA.
J Food Prot. 2021 Aug 1;84(8):1380-1384. doi: 10.4315/JFP-21-077.
Growth on solid media as sessile cells is believed to increase the desiccation tolerance of Salmonella enterica. However, the reasons behind increased resistance have not been well explored. In addition, the same effect has not been examined for other foodborne pathogens such as pathogenic Escherichia coli or Listeria monocytogenes. The purpose of this research was twofold: first, to determine the role of oxygenation during growth on the desiccation resistance of S. enterica, E. coli, and L. monocytogenes, and second, to determine the effect of sessile versus planktonic growth on the desiccation resistance of these pathogens. Three different serotypes each of Salmonella, E. coli, and L. monocytogenes were cultured in Trypticase soy broth with 0.6% yeast extract (TSBYE), with (aerobic) shaking or on TSBYE with agar under either aerobic or anaerobic conditions and harvested in the stationary phase. After adding cell suspensions to cellulose filter disks, pathogen survival was determined by enumeration before drying (0 h) and after drying for 24 h. Results showed statistical differences in harvested initial populations before drying. For Salmonella, a correlation was found between high initial population and greater survival on desiccation (P = 0.05). In addition, statistical differences (P ≤ 0.05) between survival based on growth type were identified. However, differences found were not the same for the three pathogens, or between their serotypes. In general, Salmonella and E. coli desiccation resistance followed the pattern of aerobic agar media ≥ liquid media ≥ anaerobic agar media. For L. monocytogenes serotypes, resistance to desiccation was not statistically different based on mode of growth. These results indicate growth on solid media under aerobic conditions is not always necessary for optimal desiccation survival, but may be beneficial when the desiccation resistance of the test serotype is unknown.
固体培养基上的定殖生长被认为会提高沙门氏菌的干燥耐受性。然而，其增强抗性的原因尚未得到充分探索。此外，其他食源性病原体，如致病性大肠杆菌或李斯特菌，其同样的效果尚未被检测到。本研究的目的有两个：首先，确定在生长过程中需氧对沙门氏菌、大肠杆菌和李斯特菌干燥抗性的作用；其次，确定定殖生长与浮游生长对这些病原体干燥抗性的影响。用含有 0.6%酵母提取物的胰蛋白胨大豆肉汤（TSBYE）培养三种不同血清型的沙门氏菌、大肠杆菌和李斯特菌，分别在有氧条件下进行（有氧）振荡或在有氧或厌氧条件下在 TSBYE 琼脂上培养，并在静止期收获。将细胞悬浮液添加到纤维素滤纸片后，在干燥前（0 小时）和干燥 24 小时后通过计数来确定病原体的存活情况。结果显示，在干燥前收获的初始菌量存在统计学差异。对于沙门氏菌，发现高初始菌量与干燥后更高的存活率之间存在相关性（P = 0.05）。此外，还根据生长类型确定了存活率的统计学差异（P ≤ 0.05）。然而，三种病原体之间或它们的血清型之间的差异并不相同。一般来说，沙门氏菌和大肠杆菌的干燥抗性遵循有氧琼脂培养基＞液体培养基＞厌氧琼脂培养基的模式。对于李斯特菌血清型，干燥抗性与生长方式无关，无统计学差异。这些结果表明，在有氧条件下在固体培养基上生长并不总是获得最佳干燥生存所必需的，但当测试血清型的干燥抗性未知时，可能会有益。
