Quantitative Detection of VBNC State Pseudomonas aeruginosa Contributing to Accurate Assessment of Microbial Inactivation in Drinking Water Disinfection

In harsh environments, bacteria often enter a viable but nonculturable (VBNC) state, which cannot be detected using heterotrophic plate counting (HPC). Importantly, VBNC bacteria can potentially resuscitate under favorable conditions, posing a risk to drinking water safety. This study introduces an innovative approach, combining improved quantitative polymerase chain reaction (qPCR) with propidium monoazide (PMA) dye and HPC to accurately quantify VBNC Pseudomonas aeruginosa (P. aeruginosa). The method was applied to assess the ability of various disinfection techniques to induce P. aeruginosa into the VBNC state. Different disinfection methods, including ultraviolet radiation (UV), sodium hypochlorite (NaClO), and peracetic acid (PAA), significantly reduced bacterial culturability (>99.9%), with the majority entering the VBNC state. Notably, under favorable conditions, UV-induced VBNC cells were resuscitated faster than those induced by NaClO. VBNC P. aeruginosa exhibited relatively high intracellular adenosine triphosphate (ATP) levels, indicating ongoing metabolic activity. Scanning electron microscopy (SEM) reveals that some bacteria maintained cellular integrity for UV and PAA treatment, while evident membrane disruption was observed after NaClO disinfection. This study represents a significant advancement in quantitatively detecting VBNC state P. aeruginosa, contributing to an accurate assessment of microbial inactivation during drinking water disinfection.