Abstract：
The occurrence of viable but non-culturable (VBNC) bacteria in drinking water may result in significant underestimation of viable cell counts detected by culture-based method, thus raising microbiological safety concern. Chlorine disinfection has been widely used in drinking water treatment to ensure microbiological safety. However, the effect of residual chlorine on inducing bacteria in biofilms into a VBNC state remains unclear. We determined cell numbers of Pseudomonas fluorescence in different physiological states (culturable, viable, dead) by heterotrophic plate count method and flow cytometer in a flow cell system under 0, 0.1, 0.5, 1.0 mg/L chlorine treatment. Numbers of culturable cells were 4.66 ± 0.47 Log10, 2.82 ± 0.76 Log10, 2.30 ± 1.23 Log10 (CFU/112.5 mm3) in each chlorine treatment group. However, viable cell numbers remained at 6.32 ± 0.05 Log10, 6.11 ± 0.24 Log10, 5.08 ± 0.81 Log10 (cells/112.5 mm3). Significant difference between numbers of viable and culturable cells demonstrated chlorine could induce bacteria in biofilms into a VBNC state. In this study, flow cells combination with Optical Coherence Tomography (OCT) were applied to construct an Automated experimental Platform for replicate Biofilm cultivation and structural Monitoring (APBM) system. The OCT imaging results demonstrated that changes of biofilm structure under chlorine treatment were closely related to their inherent characteristics. Biofilms with low thickness and high roughness coefficient or porosity were easier to be removed from the substratum. Biofilm with high rigid properties were more resistant to chlorine treatment. Even though >95 % bacteria in biofilms entered a VBNC state, the biofilm physical structure was still remained. This study revealed the possibility of bacteria to enter a VBNC state in drinking water biofilms and changes of biofilm structure with different characteristics under chlorine treatment, which provide reference for biofilms control in drinking water distribution systems.
摘要：
饮用水中存活但不可培养(VBNC)细菌的出现可能导致基于培养的方法检测到的活细胞计数的显著低估。从而引起人们对微生物安全的关注。氯消毒已广泛用于饮用水处理，以确保微生物安全。然而,余氯对诱导生物膜中细菌进入VBNC状态的影响尚不清楚。我们确定了不同生理状态下荧光假单胞菌的细胞数（可培养，可行的,死亡）在0、0.1、0.5、1.0mg/L氯处理下，在流动池系统中通过异养平板计数法和流式细胞仪。在每个氯处理组中,可培养细胞的数量为4.66±0.47Log10、2.82±0.76Log10、2.30±1.23Log10(CFU/112.5mm3)。然而,活细胞数保持在6.32±0.05Log10，6.11±0.24Log10，5.08±0.81Log10（细胞/112.5mm3）。活细胞和可培养细胞数量之间的显着差异表明，氯可以诱导生物膜中的细菌进入VBNC状态。在这项研究中,应用流动池与光学相干断层扫描（OCT）的组合来构建用于复制生物膜培养和结构监测（APBM）系统的自动化实验平台。OCT成像结果表明，氯处理下生物膜结构的变化与其固有特性密切相关。具有低厚度和高粗糙度系数或孔隙率的生物膜更容易从基材上去除。具有高刚性特性的生物膜对氯处理更具抗性。尽管生物膜中>95%的细菌进入VBNC状态,生物膜的物理结构仍然存在。这项研究揭示了细菌在饮用水生物膜中进入VBNC状态的可能性，以及在氯处理下生物膜结构具有不同特性的变化。为生活饮用水配水系统中生物膜的控制提供参考。
