Objective: The objective of this study was to compare of bacterial species isolated from cold and hot purified water, or from swabs of the water purifier faucets, to investigate which parts of a water purifier can affect the degree of microbial contamination in the water, and to assess levels of antibiotic susceptibility among the isolated bacteria. These studies will help design future measures to secure safety against bacterial infection due to water purifier contamination.
Methods: To investigate microbial contamination of water purifiers used in public facilities, we examined university water purifiers from July 2018 to September 2019. Bacterial colonies were collected from cold and hot water samples, and swabs of the inside of the water purifier faucets. Bacterial colonies were isolated and antibiotic susceptibility test and identified using an API kit, a Micro scan system, and MALDI-TOF MS.
Results: In the July 2018 experiment, the average bacterial colony counts were 4.4 CFU/mL inside the hot water faucet of the water purifier, and 421.6 CFU/mL inside the cold water faucet. In the September 2019 experiment, the average colonies were 0 CFU/mL inside the hot water faucet of the water purifier, and 135.1 CFU/mL inside the cold water faucet. In the January 2019 experiment, the average colonies were 1.8 CFU/mL in hot water from the water purifier, and 108CFU/mL in the cold water. In the September 2019 experiment, the average colonies were 0.09 CFU/mL in hot water from the water purifier, and 146.5 CFU/mL in the cold water, indicating no seasonal difference. Among the isolated and identified, clinically significant species were Staphylococcus aureus, Staphylococcus warneri, Acinetobacter pittii, Acinetobacter baumannii, Acinetobacter nosocomialis, Pantoea spp., and Proteus penneri, all of which showed antibiotic susceptibility.
Conclusion: In the present study, we confirmed that average colony counts in cold water and the cold water faucet of a water purifier were higher than those from hot water and the hot water faucet of a water purifier. Most of the bacteria detected in the present study were opportunistic infectious bacteria, and all showed antibiotic susceptibility. these results suggest that increasingly thorough water purifier cleaning and management will be needed in the future.