Ha Thi Mai Hoa, Yong Derrick, Lee Elizabeth Mei Yin, Kumar Prathab, Lee Yuan Kun, Zhou Weibiao
Singapore Institute of Manufacturing Technology, Singapore, Singapore.
School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore.
PLoS One. 2017 May 11;12(5):e0177571. doi: 10.1371/journal.pone.0177571. eCollection 2017.
In this study, we investigated the inactivation efficacy of endospore-forming bacteria, Bacillus pumilus, irradiated by low-energy X-rays of different beam qualities. The different low-energy X-rays studied had cut-off energies of 50, 100 and 150 keV. Bacillus pumilus spores (in biological indicator strips) were irradiated at step doses between 6.5 to 390 Gy. The resulting bacteria populations were then quantified by a pour plate method. Results showed that X-rays of lower energies were more effective in inactivating bacterial spores. In addition, an increment in bacterial population was observed at doses below 13Gy. We attributed this increase to a radiation-induced activation of bacterial spores. Four kinetic models were then evaluated for their prediction of bacterial spore behavior under irradiation. This included: (i) first-order kinetics model; (ii) Shull model; (iii) Sapru model; and (iv) probabilistic model. From R2 and AIC analyses, we noted that the probabilistic model performed the best, followed by the Sapru model. We highlighted that for simplicity in curve fitting the Sapru model should be used instead of the probabilistic model. A 12-log reduction in bacterial population (corresponding to a sterility assurance level of 10-6 as required in the sterilization of medical devices) was computed to be achievable at doses of 1000, 1600 and 2300 Gy for the three different X-ray cut-off energies respectively. These doses are an order in magnitude lesser than that required in gamma irradiation. This highlights the applicability of cheaper and safer table-top X-ray sources for sterilization application.
在本研究中，我们调查了不同束流质量的低能X射线对产芽孢细菌短小芽孢杆菌的灭活效果。所研究的不同低能X射线的截止能量分别为50、100和150 keV。将短小芽孢杆菌孢子（置于生物指示剂条中）以6.5至390 Gy的阶梯剂量进行辐照。然后通过倾注平板法对所得细菌数量进行定量。结果表明，较低能量的X射线在灭活细菌孢子方面更有效。此外，在低于13 Gy的剂量下观察到细菌数量增加。我们将这种增加归因于辐射诱导的细菌孢子活化。然后评估了四种动力学模型对辐照下细菌孢子行为的预测能力。这包括：（i）一级动力学模型；（ii）舒尔模型；（iii）萨普鲁模型；以及（iv）概率模型。通过R2和AIC分析，我们注意到概率模型表现最佳，其次是萨普鲁模型。我们强调，为了曲线拟合的简便性，应使用萨普鲁模型而非概率模型。对于三种不同的X射线截止能量，分别计算得出在1000、1600和2300 Gy的剂量下可实现细菌数量12个对数级的减少（对应于医疗器械灭菌所需的10-6无菌保证水平）。这些剂量比伽马辐照所需的剂量小一个数量级。这突出了更便宜、更安全的台式X射线源在灭菌应用中的适用性。
