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Effect of Cell Moisture on the Thermal Inactivation Rate of Bacterial Spores

机译：细胞水分对细菌孢子热失活速率的影响

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Thermal inactivation rates were determined for two strains of Bacillus subtilis var. niger spores after equilibration to various relative humidity (RH) levels. In these tests, small thin stainless-steel squares were each inoculated with a drop of spore suspension and equilibrated to 11, 33, or 85% RH. Following equilibration, the squares were placed on a hot plate preheated to 108, 125, 136, 164, or 192 C for various exposure times and then assayed for surviving organisms. The results revealed that spores of the A strain of B. subtilis were least resistant if preequilibrated to 11% RH and most resistant if preequilibrated to 85% RH. The same trend was obtained at all temperatures except 192 C, at which, no difference was noted, probably because the rapid kill time approaches the heat-up time of the stainless-steel square. The B strain of B. subtilis spores showed an opposite RH effect; that is, the cells preequilibrated to 11% RH were the most resistant. Because the two strains of spores were grown on different media, further studies were conducted at 136 C after subculturing the cells on different media. When the B strain was subcultured on the A strain medium, the pattern was reversed; the cells preequilibrated to low RH were then least resistant. Although it was not possible to reverse these cells to the original pattern by subculturing on the original B strain medium again, the pattern was altered to the point that there was no significant difference in heat resistance of these cells regardless of the preequilibration RH. The same result was obtained when the A strain was grown on the B strain medium; that is, the thermal resistance could not be reversed, but it was altered from the point where the low RH equilibrated cells were least resistant initially to the point where there was no significant difference in any of the cells regardless of what RH was used for preequilibration. The thermal resistance of spores seemed to be dependent on (i) the medium on which the spores are grown, (ii) the RH on which they are exposed before heating, and (iii) some genetic characteristic of the cell.
机译：确定了两个枯草芽孢杆菌变种的热失活率。平衡至各种相对湿度（RH）水平后的尼日尔孢子。在这些测试中，每个小的不锈钢薄方格都接种了一滴孢子悬浮液，并平衡到11、33或85％RH。平衡后，将正方形放置在预热至108、125、136、164或192 C的加热板上放置不同的暴露时间，然后分析存活的生物。结果表明，枯草芽孢杆菌A菌株的孢子如果预先平衡至11％RH，抗性最低，如果预先平衡至85％RH，抗性最高。在除192°C以外的所有温度下都获得了相同的趋势，在该温度下没有发现差异，这可能是因为快速的淬火时间接近于不锈钢方形的加热时间。枯草芽孢杆菌孢子的B株表现出相反的RH效应。也就是说，预平衡至11％RH的细胞具有最高的抵抗力。由于两种孢子菌株在不同的培养基上生长，因此在不同培养基上继代培养细胞后，在136°C进行了进一步的研究。当将B菌株在A菌株培养基上继代培养时，图案反转。预平衡至低RH的细胞则抵抗力最低。尽管不可能通过再次在原始B菌株培养基上继代培养来将这些细胞恢复为原始模式，但是无论预先平衡的RH如何，模式都会改变为这些细胞的耐热性没有显着差异。当A菌株在B菌株培养基上生长时，得到相同的结果。也就是说，热阻无法逆转，但从低RH平衡电池最初的抵抗力最小的点改变到任何一个电池都没有显着差异的点，无论使用哪种RH进行预平衡。孢子的耐热性似乎取决于（i）孢子的生长培养基，（ii）加热前暴露于其上的RH，以及（iii）细胞的某些遗传特征。

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