Occurrence of viable but non-culturable (VBNC) pathogenic bacteria in tap water of public places

● The VBNC pathogens were quantified for the first time in public tap water. ● The VBNC pathogens ranged from 1 to 103 cell equivalent/100 mL in tap water. ● Regrowth of pathogenic bacteria was found after long stagnation of tap water. ● Spatial and temporal factors explained 17.1% and 26.0% of the community variation. Viable but non-culturable (VBNC) bacteria have been detected in source water and effluent of drinking water treatment processes, leading to significant underestimation of viable cell counts. Limited information exists on VBNC bacteria in tap water, particularly in public places. To address this gap, a comprehensive nine-month study was conducted in a major city in south-eastern China, using culture-based and quantitative PCR with propidium monoazide (PMA) dye methods. Forty-five samples were collected from five representative public places (railway station, campus, hospital, shopping mall, and institution). The findings revealed that culturable bacteria represented only 0–17.51% of the viable 16S rRNA genes, suggesting that the majority of viable bacteria existed in an uncultured or VBNC state. Notably, opportunistic pathogens such as Escherichia coli, Enterococcus faecalis, Pseudomonas aeruginosa, Salmonella sp., and Shigella sp. were primarily detected as VBNC cells, with concentrations ranging from 1.03 × 100 to 3.01 × 103, 1.20 × 100 to 1.42 × 102, 1.32 × 100 to 8.82 × 100, 1.00 × 100 to 6.71 × 101, and 2.07 × 100 to 1.93 × 102 cell equivalent/100 mL, respectively. Culturable P. aeruginosa was observed in tap water after prolonged stagnation, indicating potential risks associated with bacterial regrowth. Spatial and temporal factors accounted for 17.1% and 26.0%, respectively, of the variation in tap water community structure during the sampling period, as revealed by 16S rRNA amplicon sequencing. This study provides quantitative insights into the occurrence of VBNC bacteria in tap water and highlights the need for more sensitive monitoring methods and microbial control techniques to enhance tap water safety in public locations.