Microbial flora and antimicrobial resistance in dental unit waterlines of Chongqing: An observational cross-sectional laboratory study

To identify pathogenic bacteria in dental water systems and assess microbial diversity and resistance genes, we collected water samples from 35 dental facilities in Chongqing, China. Using the VITEK 2 COMPACT system, we identified 26 strains and 13 species of opportunistic pathogens in 23 samples exceeding the standard limits. In addition, metagenomic sequencing was performed to investigate microbial diversity and resistance genes. Among the 170 collected samples, 78.2% qualified, with no significant variation across samples. However, there was a statistically significant difference in qualifying rates between hospitals of different levels ( χ2 = 7.696, P = .021). Most bacteria (80.8%) were Gram-negative and non-Enterobacteriaceae, with only 1 type belonging to the Enterobacteriaceae family. Notably abundant resistance genes included bacA, adeC, mexT, mdfA, adeJ, mdtK, emrB, and mdtB , predominantly associated with multidrug resistance (relative abundance: 71.42%). The contamination of dental unit waterlines is a concern that cannot be overlooked.