الفهرس 
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Abstract
The quality of DUW is of considerable importance to patients and dental healthcare providers because they are exposed to water and aerosols generated from the DU during routine practice. Increasing numbers of people with diminished resistance to overt and opportunistic pathogens are seeking dental treatment; these people might be particularly susceptible to infection as a result of exposure to DUW. Bacterial contamination of DUWLs output water is well documented and the contaminating bacteria include environmental species of low pathogenicity as well as potentially pathogenic opportunistic species.
P. aeruginosa is an opportunistic pathogen that has been frequently isolated from DUWL output water. It is linked to healthcare-associated infections and outbreaks, and can infect virtually all body tissues. It has the ability to form highly structured biofilms which play a protective role for the bacteria, providing increased resistance to disinfectants, antibiotics, and other environmental stresses. P. aeruginosa shows resistance to a range of antimicrobial agents through a number of intrinsic as well as acquired mechanisms, which often makes it difficult to treat any resulting infection. Application of contamination control protocols together with routine monitoring of DUWL output water are, therefore, very important to create a safe working environment for both patients and dental staff.
This study aimed at investigating the occurrence of P. aeruginosa in the water output of DUWLs and its biofilm-forming ability.
This cross-sectional study was carried out during a 5-month period, from November 2016 to March 2017, on a total of 147 water samples randomly collected from 7 dental clinics at the Alexandria Dental Research Center. A total of 140 samples (120 ml) each were collected randomly from 20 DUs during 20 weeks as follows:
a) Water samples from the outlets of each of the high-speed handpiece, the air/water syringe and the cup filler waterlines of the 20 DUs. (120 samples)
b) DU reservoir water samples (to assess the water quality before entering the high- speed handpiece and the air/water syringe waterlines; 20 samples)
The water samples from the output of the DUWLs were collected on two separate occasions; at the beginning of the working day and at midday when the DUs were being used. In addition, 7 tap water samples, (120ml) each, were collected from the taps adjacent to the DUs in each clinic to assess the water quality before entering the cup filler waterline.
All samples were transferred without delay to the microbiology laboratory at HIPH in an ice box and processed within 1-4 hours of collection. The collected samples were subjected to enumeration of the viable HPC bacteria by the standard pour plate method, isolation and identification of P. aeruginosa by MF technique, determination of the antimicrobial susceptibility patterns of the P.aeruginosa isolates and detection of the BFA of the P.aeruginosa isolates by both the TCP method and the TM.
The results of this study can be summarized as follows:
1. According to the Egyptian standards for drinking water, of 120 examined DUWL output water samples, 14 (11.7%) were acceptable regarding HPC, and 106 (88.3%) were found to be unacceptable. For the water reservoirs, out of 20 examined samples, 4 (20.0%) were acceptable, and 16 (80.0%) were unacceptable. For the tap water, all of the 7 examined samples were acceptable regarding HPC.
2. The mean values of HPC of tap water, reservoir water, and DUWL output water samples were 3.4 ×10, 2.2 ×104 and 2.9 ×104 CFU/ml, respectively.
3. The mean overall values of HPC in the DUWL output water in relation to the time of collection were 3.6 ×104 CFU/ml before clinical activity and 2.2 ×104 after clinical activity.
4. The mean values of HPC of the water samples collected from the clinics of pediatric dentistry, implants, conservative treatment, oral surgery, fixed prosthodontics, periodontics and minor operations were 8.1×104, 2.8 ×104, 1.2 ×104, 6.5 ×103, 1.9
×103, 3.6 ×102 and 7.9 ×10 CFU/ml, respectively. The corresponding percentages of
acceptability according to the Egyptian standard were 2.8%, 6.7%, 16.7%, 26.7%,
6.7%, 40.0% and 40.0%, respectively.
5. Out of 147 examined water samples, P. aeruginosa was isolated from 9 cup filler waterline output samples. The samples collected from the other sources did not yield any P. aeruginosa isolates.
6. In relation to P. aeruginosa, the percentages of acceptability of the examined water samples from the clinics of periodontics, conservative treatment, pediatric dentistry, fixed prosthodontics, minor operations, oral surgery and implants were 86.7%, 91.7%, 91.7%, 93.3%, 100.0%, 100.0%, and 100.0%, respectively.
7. All of the 9 P. aeruginosa isolates were sensitive to the 14 tested antimicrobial agents; piperacillin, Piperacillin/Tazobactam, ticarcillin/clavulanate, ceftazidime, cefepime, aztreonam, imipenem, meropenem, colistin, polymyxin B, gentamicin, tobramycin, amikacin and ciprofloxacin.
8. The BFA of the 9 P.aeruginosa isolates was examined using the standard TCP method, the modified TCP method and the TM. The number of strains that showed positive BFA were 6 (66.7%), 5 (55.6%) and 4 (44.4%), respectively.
It can be concluded from this study that:
1. According to the Egyptian standards, DUWLs output water showed inferior bacteriological quality relative to the source water that supplied the waterlines.
2. The high-speed handpiece water samples showed a higher level of bacteriological contamination than those from the air/water syringe.
3. By following the changes in the level of HPC bacterial contamination in DUWL water, the waterlines most likely contaminated with P. aeruginosa can be highlighted.
4. P. aeruginosa isolates from DUWLs may not be as resistant to antibiotics as what is reported in the literature about isolates from clinical specimens.
5. Despite their inability to form a biofilm, some P. aeruginosa isolates may persist in DUWLs through colonizing pre-formed biofilms.