Microbiological evaluation and antibiotic susceptibility of dental unit water systems in general dental practice

The microbial quality of water in a dental unit water systems (DUWS) is of considerable importance because patients and dental staff are regularly exposed to water and aerosol generated from the dental units. The objective of this study was to evaluate the 20 DUWS in general dental practices and to determine the antibiotic susceptibility of the colonizing bacteria.

Three water and one biofilm samples from each DUWS were investigated for total viable count (TVC), oral streptococci, Pseudomonas spp., Enterobacteria, Candida albicans and Legionella pneumophila.

A total of 44 morphologically different colonies were obtained from water samples and 20 types of colonies (45.5%) could be identified using API test strips. The mean TVC values were 4.36 log CFU ml(-1) for source waters, 4.95 log CFU ml(-1) for 3-in-1 syringe samples, 4.91 log CFU ml(-1) for air rotor samples and 3.66 log CFU cm(-2) for biofilm samples. Susceptibilities of the isolates were tested against piperacillin, ampicillin, ceftazidime, meropenem, gentamicin, tetracycline, ofloxacin and chloramphenicol by using microdilution method according to NCCLS. The meropenem and ofloxacin have shown the broadest spectrum against to the tested isolates.

The study emphasizes the need for effective mechanisms to reduce the microbial contamination in DUWS, and highlights the risk for cross-infection in general dental practice.