Bacterial contamination of dental chair units in a modern dental hospital caused by leakage from suction system hoses containing extensive biofilm.

Within six months of opening of the new Dublin Dental Hospital in September 1998, areas of corrosion were observed on many of the baseplates of the hospital's 103 dental chair units (DCUs) at the site of attachment of the suction hoses. The corroded areas were heavily contaminated with Pseudomonas spp. and related genera posing a risk of cross-infection, particularly for immunocompromised patients. These species were used as marker organisms to investigate the source of the contamination. P. aeruginosa was the predominant species recovered from 41 selected DCU baseplates (61% prevalence), whereas P. putida (46% prevalence) and P. aeruginosa (43% prevalence) were predominant at the attachment ends of 37 selected high-volume suction hoses. Forty-one selected isolates of P. aeruginosa from 13 DCU baseplates, 16 high-volume suction hoses and 12 coarse filter housings (another suction system site) from 19 separate DCUs were serotyped to determine the similarity of isolates at each site. The majority of isolates (68.3%) belonged to serotype O:10, while the remainder belonged to serotypes O:6 (7.3%), O:11 (7.3%), O:14 (9.8%) and O:5/O:16 (7.3%). Of the isolates from DCU baseplates, additional isolates with the same serotype were recovered from other suction system sites in 10/13 (77%) cases. Isolates of only one serotype were recovered from each of the 19 DCUs investigated. Forty-one serotyped isolates were also subject to computer-assisted analysis of SpeI-generated DNA fingerprint profiles, and similarity coefficient (S(AB)s) values were calculated for each pairwise combination of isolate profiles. The data obtained showed that the isolates consisted of two distinct main populations, each containing separate clades corresponding to specific serotypes. Serotype O:6 (three isolates), O:11 (three isolates) and O:5/O:16 (three isolates) belonged to a single strain in each case. Serotypes O:14 (four isolates) and O:10 (28 isolates) belonged to two strains in each case. The two serotype O:10 strains, termed fingerprint groups I (four isolates from three DCUs) and II (24 isolates from 10 DCUs), were the most distantly related of all the strains identified. These findings demonstrated that the hospital DCUs had become colonized with a small number of P. aeruginosa strains, one of which (serotype O:10, fingerprint group II) predominated. These results also confirmed that DCU baseplate contamination was most likely to be due to leakage from suction system hoses at the baseplate attachment sites, probably due to loosening during use. Replacement hose connectors that firmly retained the suction hoses in the attachment sites so that they could not be loosened by movement of the suction hoses solved this problem, and eliminated further contamination of the DCU baseplates.

Effective control of dental chair unit waterline biofilm and marked reduction of bacterial contamination of output water using two peroxide-based disinfectants.

Bacterial biofilm in dental unit waterlines (DUWs) is a widespread problem, and poses a potentially significant risk of infection to dental staff and patients, particularly those who are medically compromised or immunocompromised. The purpose of the present study was to investigate the level of bacterial contamination of dental chair unit output water in the Dublin Dental Hospital, and to investigate the efficacy of two hydrogen peroxide-based disinfectants in reducing bacterial loads to < or =200 cfu/mL as recommended by the American Dental Association. The chemical quality of dental chair unit input and output water was well within the limits recommended for potable water. Water supplied to the units yielded an average aerobic heterotrophic bacterial cell density of 184 cfu/mL. However, the corresponding density in output water was considerably higher; the average cell density in water from the three-in-one air/water syringes and cup fillers in 12 chairs was 8200 and 4300 cfu/mL, respectively. Dental unit water obtained from 18 separate reservoir-supplied units in general practices in the Dublin area yielded an average of 66000 cfu/mL. The bacterial species found were predominantly environmental organisms, which were also present at low levels in the input water. Some of the species identified (e.g., Burkholderia cepacia and Pseudomonas fluorescens) are known opportunistic pathogens. The capacity of two disinfectants, Sterilex Ultra and Sanosil, to reduce bacterial contamination to safe levels was compared. In a controlled study, once weekly overnight (15 h) disinfection using either agent reduced the bacterial density to below the American Dental Association recommended level of 200 cfu/mL. However, once disinfection ceased the bacterial loads increased to unacceptably high levels within three weeks. Electron microscopic analysis showed that both disinfectants markedly reduced biofilm in the DUWs, but the biofilm rapidly became extensive again when once weekly disinfection ceased. While both disinfectants were equally effective in lowering the bacterial counts to acceptable levels, Sterilex Ultra was associated with clogging of DUWs in some dental chair units after repeated usage, suggesting that Sanosil is a more suitable agent for routine use.