Formation mechanisms of viable but nonculturable bacteria through induction by light-based disinfection and their antibiotic resistance gene transfer risk: A review

Disinfection technologies, especially light-based disinfection, have undergone tremendous development and innovation, but this treatment can cause bacteria to enter viable but nonculturable (VBNC) state. Due to their strong tolerance, VBNC bacteria cannot be completely removed by disinfection technologies, thereby posing a potential risk for antibiotic resistance gene (ARG) transfer. Therefore, to better understand VBNC bacteria and interpret potential transfer of ARGs, this article systematically reviewed changes in morphology, physiology and virulence of bacteria after entering VBNC state. In addition, this article reviewed quantitative detection methods of VBNC bacteria, such as cell membrane integrity-mediated LIVE/DEAD Baclight assay, qPCR-based assays, and phage-based detection methods, concluding that there is still a lack of in-situ and real-time detection methods for VBNC bacteria. Health risks and environmental application value of VBNC bacteria were then valuated, with data indicating that VBNC bacteria have great value in the domain of microbial utilization. Furthermore, the induction conditions (especially by light-based disinfection) and formation mechanisms of VBNC bacteria were highlighted. Formation mechanisms mainly involve stringent response, general stress response system and toxin-antitoxin (TA) system. Moreover, horizontal gene transfer (HGT) of ARGs during and after the formation of VBNC bacteria induced by light-based disinfection was evaluated. It was found that ARGs may be transferred through conjugation, transformation and transduction. Finally, current deficiencies and future challenges for the transformation of VBNC bacteria, especially those influenced by light-based disinfection technologies, were summarized. This review provides new insights into detection methods, formation mechanisms, environmental applications and potential ARG transfer risks of VBNC bacteria.