NIZO, 6718 ZB Ede, the Netherlands; Top Institute Food and Nutrition, 6709 PA, Wageningen, the Netherlands.
Laboratory of Food Microbiology, Wageningen University, 6700 AA Wageningen, the Netherlands; Top Institute Food and Nutrition, 6709 PA, Wageningen, the Netherlands.
Int J Food Microbiol. 2019 Feb 16;291:161-172. doi: 10.1016/j.ijfoodmicro.2018.11.005. Epub 2018 Nov 10.
In this study, different methods were evaluated for enumeration of spores of G. stearothermophilus, different sporulation methods were assessed for yields and wet heat resistances of obtained spores, and subsequently, the variation in heat resistances of spores was determined. Overall, tryptone soya agar (TSA) was the most suitable medium for enumeration of spores of this thermophilic bacterium. Sporulation on different media both at 55 and at 61 °C led to considerable variation in spore heat resistance. The heat resistance of spores was highest upon sporulation on medium supplemented with free ions of calcium, potassium, magnesium and manganese (CaKMgMn). For 18 different G. stearothermophilus strains that were isolated from various sources, spores were subsequently produced on nutrient agar supplemented with CaKMgMn at 55 °C. Strain ATCC 12980, also known as 9A20, which is commonly used in steam sterilization tests was included. The survival of spores of all strains was assessed at 125 °C and 130 °C using two independent spore batches per strain. The mean D for spores of the 18 strains was 1.1 min (95% PI 0.48-2.3 min) and the mean D was 0.37 min (95% PI 0.17-0.82 min). For spore inactivation of these 18 strains, a z-value of 11.1 °C was estimated, resulting in an estimated D-value of 2.4 min (95% PI 1.1-5.2) at the reference temperature 121.1 °C. Based on the data sets obtained in this study, it was found that the variability in spore heat resistance could largely be attributed to strain variability and conditions used during sporulation (especially the sporulation medium); reproduction and experimental variabilities were much smaller. The established variabilities were compared with the overall variability in spore heat resistance of G. stearothermophilus based on a meta-analysis of reported D-values. The data presented indicate that strain variability and history of sporulation each account for approximately half of the overall variability observed with respect to the heat resistance of spores of G. stearothermophilus. The findings presented in this study allow for optimal recovery of G. stearothermophilus spores from foods and a better understanding of factors that determine the heat resistance properties of spores of G. stearothermophilus. Moreover, this study once more underlines the limited effects of heat treatments used in the food industry on inactivation of spores of this bacterium.
在这项研究中，评估了不同的方法来计数嗜热脂肪芽孢杆菌的孢子，评估了不同的产孢方法对获得的孢子的产率和湿热抗性的影响，随后确定了孢子耐热性的变化。总的来说，胰蛋白胨大豆琼脂（TSA）是最适合计数这种嗜热细菌孢子的培养基。在 55 和 61°C 下在不同培养基上产孢会导致孢子耐热性的显著变化。在补充有游离钙、钾、镁和锰离子的培养基上产孢时，孢子的耐热性最高。对于从各种来源分离的 18 株不同的嗜热脂肪芽孢杆菌菌株，随后在补充有 CaKMgMn 的营养琼脂上于 55°C 产孢。该研究还包括了在蒸汽灭菌试验中常用的 ATCC 12980，也称为 9A20。使用每个菌株的两个独立孢子批次评估所有菌株的孢子的存活情况，在 125°C 和 130°C 下进行。18 株菌株的孢子 D 值平均值为 1.1 分钟（95%PI 0.48-2.3 分钟），平均 D 值为 0.37 分钟（95%PI 0.17-0.82 分钟）。对于这些 18 株菌株的孢子失活，估计了 11.1°C 的 z 值，导致在参考温度 121.1°C 下估计的 D 值为 2.4 分钟（95%PI 1.1-5.2）。基于本研究中获得的数据，发现孢子耐热性的可变性主要归因于菌株变异性和产孢过程中使用的条件（特别是产孢培养基）；繁殖和实验变异性要小得多。将建立的变异性与基于报道的 D 值的嗜热脂肪芽孢杆菌孢子耐热性的总变异性进行了比较。提出的数据表明，菌株变异性和产孢历史各自占嗜热脂肪芽孢杆菌孢子耐热性观察到的总变异性的大约一半。本研究的结果允许从食品中最佳回收嗜热脂肪芽孢杆菌孢子，并更好地理解决定嗜热脂肪芽孢杆菌孢子耐热性的因素。此外，这项研究再次强调了食品工业中使用的热处理对该细菌孢子失活的有限影响。
