Microbial contamination in dental unit waterlines and its disinfection method

Abstract:

Objective To isolate and identify microorganism contaminated in dental unit waterlines (DUWLs), evaluate current disinfection and infection control measures through the resistance of dominant pathogens to different disinfectants. Methods DUWLs in a tertiary first-class dental hospital were selected as the research object, microorganisms in DUWLs were cultured and conducted colony counting, dominant bacteria were isolated and identified by mass spectrometry, resistance of dominant bacteria to different disinfectants was evaluated by minimum inhibitory concentration (MIC) test and minimum bactericidal concentration (MBC) test, resistance of Mycobacterium mucogenicum was compared with that of standard strain (Mycobacterium chelonei subsp.abscessus) by suspension quantitative germicidal method. Results Detection rate of colonies in 48 water specimens from 24 DUWLs was 100.00%, the average number of colony was (2.25±1.43)×10⁵ CFU/mL, 9 kinds of contaminated microorganisms were isolated, the dominant pathogen was Mycobacterium mucogenicum (35.72%), followed by fungi (21.43%). MICs of the isolated Mycobacterium mucogenicum to chlorhexidine acetate, sodium hypochlorite, peracetic acid, and hydrogen peroxide were 1.5, 500, 5 and 100 mg/L respectively, and MBC were 3, 500, 10 and 200 mg/L respectively, resistance to sodium hypochlorite was close to the standard strain; 0.5% chlorhexidine acetate could not effectively kill the isolated Mycobacterium mucogenicum and standard strain Mycobacterium chelonei subsp.abscessus within 30 minutes, 0.1% sodium hypochlorite, 3% hydrogen peroxide and 0.1% peracetic acid could effectively kill the isolated Mycobacterium mucogenicum and standard strain Mycobacterium chelonei subsp.abscessus within 30 minutes. Conclusion Non-tuberculous mycobacterium, which has strong resistance to chlorine-containing disinfectant, has replaced Pseudomonas aeruginosa and Legionella as the dominant flora in DUWLs of the hospital selected in this study, appropriate disinfectant types, concentration, effective action time and use frequency should be selected for the disinfection of DUWLs.