Hoffman R K, Gambill V M, Buchanan L M
Appl Microbiol. 1968 Aug;16(8):1240-4. doi: 10.1128/am.16.8.1240-1244.1968.
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.
在将两株枯草芽孢杆菌黑色变种孢子平衡至不同相对湿度（RH）水平后，测定了其热失活率。在这些试验中，将小的薄不锈钢方块分别接种一滴孢子悬液，并平衡至11%、33%或85%的相对湿度。平衡后，将方块置于预热至108、125、136、164或192℃的热板上，暴露不同时间，然后检测存活的生物体。结果显示，枯草芽孢杆菌A菌株的孢子在预平衡至11%相对湿度时抗性最低，而在预平衡至85%相对湿度时抗性最高。除192℃外，在所有温度下均得到相同趋势，在192℃时未观察到差异，可能是因为快速杀灭时间接近不锈钢方块的升温时间。枯草芽孢杆菌B菌株的孢子表现出相反的相对湿度效应；即预平衡至11%相对湿度的细胞抗性最强。由于两株孢子在不同培养基上生长，在将细胞接种到不同培养基上继代培养后，于136℃进行了进一步研究。当B菌株在A菌株培养基上继代培养时，模式发生了逆转；预平衡至低相对湿度的细胞此时抗性最低。尽管再次在原始B菌株培养基上继代培养无法使这些细胞恢复到原始模式，但模式改变到这样一个程度，即无论预平衡相对湿度如何，这些细胞的耐热性没有显著差异。当A菌株在B菌株培养基上生长时也得到了相同结果；即耐热性无法逆转，但从最初低相对湿度平衡的细胞抗性最低的点改变到无论使用何种相对湿度进行预平衡，任何细胞之间都没有显著差异的点。孢子的耐热性似乎取决于：（i）孢子生长的培养基；（ii）加热前暴露的相对湿度；以及（iii）细胞的一些遗传特性。
