SEJ_2-2017_Articol_AlKhabuli
ORAL MICROBIOLOGY
THE MICROBIAL PROFILES OF DENTAL UNIT WATERLINES IN A
Original Articles
DENTAL SCHOOL CLINIC
Juma AlKhabuli1a*, Roumaissa Belkadi1b, Mustafa Tattan1c
1
RAK College of Dental Sciences, RAK Medical and Health Sciences University, Ras Al Khaimah, UAE
a
BDS, MDS, MFDS RCPS (Glasg), FICD, PhD, Associate Professor, Chairperson, Basic Medical Sciences
Students at RAK College of Dental Sciences, RAK Medical and Health Sciences University, Ras Al Khaimah, UAE
b,c
Received: Februry 27, 2016
Revised: April 12, 2016
Accepted: March 07, 2017
Published: March 09, 2017
Academic Editor: Marian Neguț, MD, PhD, Acad (ASM), “Carol Davila” University of Medicine and Pharmacy Bucharest, Bucharest, Romania
Cite this article:
Alkhabuli J, Belkadi R, Tattan M. The microbial profiles of dental unit waterlines in a dental school clinic. Stoma Edu J. 2017;4(2):126-132.
ABSTRACT DOI: 10.25241/stomaeduj.2017.4(2).art.5
Background: The microbiological quality of water delivered in dental units is of considerable
importance since patients and the dental staff are regularly exposed to aerosol and splatter generated
from dental equipments. Dental-Unit Waterlines (DUWLs) structure favors biofilm formation and
subsequent bacterial colonization. Concerns have recently been raised with regard to potential risk
of infection from contaminated DUWLs especially in immunocompromised patients.
Objectives: The study aimed to evaluate the microbial contamination of DUWLs at RAK College
of Dental Sciences (RAKCODS) and whether it meets the Centre of Disease Control’s (CDC)
recommendations for water used in non-surgical procedures (≤500 CFU/ml of heterotrophic
bacteria).
Materials and Methods: Ninety water samples were collected from the Main Water Source (MWS),
Distilled Water Source (DWS) and 12 random functioning dental units at RAKCODS receiving water
either directly through water pipes or from distilled water bottles attached to the units. Bacterial
enumeration and molecular identification were performed.
Results: The MWS had the lowest bacterial count (499 CFU/ml).The bottled units contained significantly
higher numbers of CFU (2632±1231.783) compared to non-bottled units (1484.75±1395.093),
p<0.02. Ralstonia spp. was the most common bacteria present in the MWS and DWS (in 96% of the
samples). Other bacteria were Sphingomonas paucimobilis 88.8% and Leifsonia spp. 73.5%.
Conclusion: There is a need for regular water monitoring at dental clinics, in addition to regular
maintenance and disinfection programs to ensure quality water delivery that meets the CDC
guidelines for non-surgical water.
Keywords: Maintaining dental unit waterlines, microbial contamination, biofilm formation, non-
surgical water.
1. Introduction through a process known as back-siphonage. Back-
In the dental office, infection control in terms siphonage is the process of aspiring oral fluids
of self-protection, instrument sterilization and as a result of the temporary negative pressure
surface disinfection is given great importance produced when the drill stops rotating while still in
due to its huge impact on the patient’s health. the patient’s mouth2,3 due to lack of anti-retraction
The microbiological quality of water running in valves.4 In certain conducted studies, it has been
the Dental-Unit Water Lines (DUWLs) however is observed that about 1mL of oral fluids is retracted
mostly overlooked. in old as well as some new dental equipments.3
Contaminated water in DUWLs causes a health This process increases the risk of cross infection
threat to both patients and dental staff who are as oral fluids are retracted from one patient’s
regularly exposed to aerosol and splatter.1 The oral cavity, grown within the DUWL, and spread
patients with the highest risk of infection from through aerosol or splatter to other patients or
contaminated water are immunocompromised healthcare personnel.
patients, elderly patients and patients with recent Dental unit water systems’ narrow lumens and
surgeries and open wounds. small bores, in conjunction with the long periods
Bacteria responsible for DUWL contamination of stagnant water favor the formation of biofilms
can originate from municipal water piped into which adhere to the inner surfaces of the lines
the dental chair unit or from patients’ oral cavities and serve as a haven for pathogens protecting
*Corresponding author:
Juma Alkhabuli BDS, MDentSci, MFDS RCPS (Glas) FICD, PhD
Associate Professor and Head of Basic Dental Sciences Department, RAK College of Dental Sciences, Ras Alkhaimah Medical and Health Sciences University , P.O.Box 12973, Ras Alkhaimah, UAE,
Tel: +97172222593/2269, Fax: +971 7 222 2 634, e-mail: juma@rakmhsu.ac.ae
126 Stoma Edu J. 2017;4(2): 126-132 http://www.stomaeduj.com
THE MICROBIAL PROFILES OF DENTAL UNIT WATERLINES IN A
DENTAL SCHOOL CLINIC
the bacteria both from being washed away by the with the main pipe, which ejects dosed chemicals
Original Articles
water flow and from many types of antimicrobial into the water stream (Fig. 1). These non-toxic
water treatments.4 Although the microorganisms chemicals are commercially available under the
found in biofilms are predominantly harmless, name “MembraClean Plus Disinfectants”, which
gram-negative water bacteria, opportunistic presumably have antimicrobial action, including
pathogens such as Pseudomonas aeruginosa, bacteria, fungus and algae, and prevent scale or
Legionella pneumophila, and non-tuberculous biofilm formation. The supplier of the chemicals
mycobacteria may also be found.5 never discloses the actual chemical composition.
The opportunistic pathogens of Pseudomonas Nevertheless, the product is approved by the local
spp. were found, in a number of cases, to be the authority for drugs and chemicals control, UAE.
predominant species isolated from DUWL.2,6 In Further search for the chemicals details was tried
a study conducted by Dr. Barbeau et al. (1998), but to no avail.
it was stated that pathogens like Pseudomonas The main aim of this study was to evaluate the
aeruginosa, Legionella pneumophila and microbial contamination of DUWLs in RAKCODS by
nontuberculous mycobacteria do not merely determining composition as well as concentration
survive in DUWL, but also proliferate over time of microflora and whether it meets the Centre
with enhancing resistance by the inhabited of Disease Control’s (CDC) recommendations
biofilm as they wait for a susceptible host.7 This for water used in non-surgical procedures. The
kind of contamination is especially dangerous, research highlights on the importance of regular
and crucial enough not to be overlooked or water monitoring as well as antimicrobial water
taken lightly, particularly when treatment of treatments to assure quality water delivered.
immunocompromised patients is considered, such
as cases of cystic fibrosis or AIDS.8,9,10 2. Materials and Methods
In 1995, the American Dental Association (ADA) 2.1. Sample collection
Board of Trustees and ADA council on Scientific The study material included water samples from
Affairs adopted a statement on DUWLs. The the main water source, distilled water source and
statement recommended improving the dental 12 functioning dental units at RAKCODS randomly.
unit design so that by the year 2000,water delivered The main age of the dental units is 3 years of
to patients during non-surgical dental procedures service. From each collecting point, 3 samples
would contain no more than 200 colony forming were collected at interval over a period of 6
units (CFU)/ml of aerobic mesophilic heterotrophic weeks. Three water samples were collected from
bacteria.1,11,12 This was equivalent to the standard the Main Water Source (MWS) before entering
for dialysate fluid. RAKCODS water pipe-lines, 3 water samples from
In 2003, the Center for Disease Control’s (CDC) the Distilled Water Source (DWS) (water distilling
guidelines for infection control in dental health machine) and 3 samples were collected from each
care settings stated that coolant/irrigant water point of the dental units; including Distilled Water
used in non-surgical dental procedures should Bottles (DWB) and dental units’ Water Line Tubes
meet the Environmental Protection Agency (EPA) (WLT) connecting the Hand pieces and Ultrasonic
regulatory standards for drinking water which is scaler tips (H/S). Care was taken to collect the
less than or equal to 500 CFU/ml of heterotrophic samples in aseptic condition to avoid any external
bacteria.1,13 microbial contamination. Most of the samples
RAK College of Dental Sciences (RAKCODS), UAE were collected between 10.30 am and 12.30 pm
moved into a new building in 2011. The main water using sterile air-tight containers. All dental units
supply to the college is through the Municipality included in the study were operating at the time of
network. The water is collected in ground reservoir sample collection. Approximately, 15 ml of water
then pumped to the roof tank. From the latter, was collected from each collecting point in pre-
water is delivered through water pipes network labelled, air-tight sterile containers. The containers
to the whole building including the dental units were labeled according to the point of water
(Fig. 1). The majority of dental units (90%) receive collection and reference number of the dental
water directly through the water pipes. A limited unit. The water outlet, like hand pieces, scaler tips,
number (10%) of dental units receive distilled water line tubes were flushed for few seconds
water via bottles attached to the units, which are before taking the sample. In total 90 samples were
filled frequently from the water distilling machine collected successfully. The water samples were
as required (Fig. 1). then transferred to the microbiology department,
As part of the sanitary measures taken by the RAK Medical and Health Sciences University
administration, the main water (Municipality (RAKMHSU) within 3 hours from collection time for
water) is regularly examined for microbial load microbial analysis.
and other chemical ingredients to ensure that it 2.2. Laboratory procedures
meets the recommended standard by the local • Pour plate technique for bacterial enumeration
authority. However, the performed water analysis (Standard Plate Count):
never included samples from the dental units. In the RAKCOMS microbiology lab, pour
Before water is pumped to the roof tank a small plate technique for bacterial enumeration was
device “Solenoid-Driven Metering Pump” is fixed performed as follows:
Stomatology Edu Journal 127
THE MICROBIAL PROFILES OF DENTAL UNIT WATERLINES IN A
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Original Articles
Roof tank
Chairs connected Chairs receiving
directly with water distiled water
pipe lines through attached
bottles
Hand piece/
scaler* (H/S)
MembraClean Plus
Disinfectant
Main water source*
(MWS) Water line
Water tube* (WLT) *
pump
Distiled water Distilled water source*
bottle (DWB) (DWS)
Ground
reservoire
* = collecting point
Figure 1. The diagram of the RAKCODS Dental Units’ water supply system and the points of samples collection.
Plate Count Agar (HiMedia, India) was prepared amplification uses PCR Primers (Universal), forward:
according to standard procedure and then cooled 27F - 5’- AGAGTTTGATCMTGGC TCAG - 3’, Reverse:
at 44-46°C. Serial dilutions were prepared from the 1492 R - 5’- TACGGYTACCTTGTTACGACTT - 3’. DNA
water samples in addition to undiluted sample (1:1, sequencing using BigDye® Terminator v1.1 Cycle
1:10, 1:100). One ml of each sample or dilution Sequencing Kit, Sequencing reaction for Forward
was transferred to the properly labeled sterile (518F) and Reverse (800R), Data analysis - Sequencing
Petri dish. Approximately 15ml of the cooled agar Analysis Software v5.2. Bioinformatics tools used
medium was then poured into each Petri dish. The Fasta format conversion of both sequences – NCBI,
sample and agar were then mixed by rotating the Pairwise sequence alignment – LALIGN software,
plate several times. After the media has solidified, trimming of final sequence, NCBI blast search, Similar
the plates were inverted and incubated at 35°C sequence identification, identification of bacteria.
for 48-72 hours. After incubation, the count of
colonies, mean and standard deviation were 3. Results
calculated. Table 1 shows the total count of bacteria (CFU/ml) in
• Molecular identification of bacteria: water samples collected from the Main Water Source,
Pure cultures of the isolated bacteria were sent for the Distilled Water Source and 12 dental units of
molecular identification in AccuVis Bio laboratories RAKCODS, counted according to ADA guidelines
in Abu Dhabi University Campus, Abu Dhabi, (Table 1).
UAE. Bacterial 16S rRNA gene sequencing was Based on the ADA guidelines, which state that water
performed according to the following protocol: used in dental treatment should contain a bacterial
Bacterial DNA isolation AccuVis Bio’s Bacterial level of ≤200 CFU/ml, the majority of samples collected
Genomic DNA Isolation Kit (AV1003). PCR in our study showed CFU above the standard.
Table 1. Bacterial count in the water samples taken from different collecting points
Site of collection Total number of Number (%) of Number (%) of Mean number of
collected samples with samples with CFU/ml±SD
samples 0–200 CFU*/ml >200 CFU/m
Main Water Source 3 0 (0%) 3 (100%) 499±345
Distilled Water Source 3 0 (0%) 3 (100%) 1538±1165
Distilled Water Bottle 12 0 (0%) 12 (100%) 2397±1403
Water Line Tube 36 5 (14%) 31 (86%) 1867±1434
Handpiece/Ultrasonic 36 2 (6%) 34 (94%) 2000±1535
Scaler
*CFU: colony forming units
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THE MICROBIAL PROFILES OF DENTAL UNIT WATERLINES IN A
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Original Articles
Table 2. The bacterial distribution of the water samples according to the collecting points and isolated bacteria
Total number Number (%) of samples in which the following bacteria were isolated
Source/site of sample of collected
collection samples Ralstonia spp. Sphingomonas Leifsonia spp. Brevundimonas Pseudomonas
paucimobilis aurantiaca aeruginosa
Main Water Source 3 1 (33.3%) 2 (66.7%) 3 (100%) 0 (0%) 0 (0%)
Distilled Water Source 3 3 (100%) 3 (100%) 2 (66.7%) 1 (33.3%) 0 (0%)
Distilled Water Bottle 12 12 (100%) 10 (83.3%) 10 (83.3%) 6 (50%) 3 (25%)
Handpiece/Ultrasonic Scaler 36 35 (97%) 33 (91.7%) 24 (66.7%) 14 (38.9%) 3 (8.3%)
Water Line Tube 36 36 (100%) 32 (88.8%) 27 (75%) 13 (36.1%) 3 (8.3%)
Total 90 87 (96%) 80 (88.8%) 66 (73.5%) 34 (37.8%) 9 (10%)
The CDC recommended that non-surgical dental drinkable water. The fact that MWS samples contained
water should have a heterotrophic plate count (HPC) significantly lower CFU/ml of bacteria compared
of ≤500 CFU/ml. The only samples that fulfilled to the DWB, WLT or H/S clearly indicates that the
this criterion were the Main Water Source samples dental water pipelines provide good environment for
(499 CFU/ml) which is equal to the levels of HPC in bacteria to thrive.
drinkable water. When bottled dental units were replaced with new
Since the dental units’ water supply systems were dental units, the average CFU/ml was reduced
of two types as shown in Fig. 1, it was found that the dramatically. This result substantiates the assumption
bottled units contained significantly higher numbers that the DWB was the main source of contamination.
of CFU (2632±1231.783) compared to the non- In the examined water samples from the dental units,
bottled units (1484.75±1395.093), p<0.02. bacteria of the Pseudomonadaceae family were the
RAKCODS had a prescheduled plan to replace all of most common. These obligate aerobic, motile, gram
the distilled water bottled dental units with new units negative bacilli are widely spread and have the ability
receiving direct water connection. The units were to survive and grow almost in any environment. Their
installed on time (September 2015) and were allowed presence is associated with the main water supply and
to work for 4 months. Random water samples from failure of disinfection methods to eradicate them totally
7 of the newly installed dental units. Two samples or even reduce their counts. The isolated bacteria
from each water outlets (water/air syringe and hand tend to categorize as non-fermenting gram-negative
piece tubes) were collected in the same manner as bacilli (NFGNB) which are a group of organisms that
described earlier and the bacterial colonies per ml either do not utilize glucose as a source of energy or
were counted. The average CFU/ml of these samples utilize it oxidatively.14
were compared with the average counts of water line Pseudomonas aeruginosa, species of Pseudomonas
tubes of the previous bottled units. The newly installed genus can be recovered from the oral cavity of 4% of
dental unit counts showed remarkable reduction in healthy individuals4 and this indicates the possibility
the number of CFU/ml (720, SD±969). of these microorganisms getting aspirated into the
Table 2 shows the isolated bacteria and number DUWLs through a defective check valve and colonized
of water samples contaminated with each type of in the waterlines. This is a drawback due to the fact
bacteria out of the total number of samples collected that water after having passed through DUWL, flows
from the Main Water Source, the Distilled Water through hand pieces during treatment and forms
Source and the 12 dental units (Table 2). aerosol and splatter therefore increasing the chances
Ralstonia spp. was the most common bacteria in the of cross infection especially in immunocompromised
MWS, DWS and dental units’ WLT, as it was found in patients.
96% of the collected samples. The other common Following is a list of bacteria tested for in our study, in
isolated bacteria were Sphingomonas paucimobilis the order of their prevalence:
88.8%, Leifsonia spp.(73.5%), Brevundimonas 4.1. Ralstonia spp.
aurantiaca (37.8%) and Pseudomonas aeruginosa Ralstonia spp. was the most common type of bacteria
(10%). present in the MWS, DWS and dental units’ WLT. It was
found in 96% of the collected samples. This finding is
4. Discussion in accordance with many of the previous studies.15,16,17
The majority of the collected samples in this study This bacterium is known to be isolated from water
showed CFU above the standards for drinking water regardless of its source. It could be isolated from
or water used for dental procedures according to municipal drinking water, bottled water, dental
the CDC guidelines. The only samples that fulfilled waterline tubes, hospital water supplies, standard
this criterion were the MWS samples with an HPC of purified water, laboratory-based high-purity water
(499 CFU/ml), which is equal to the levels of HPC in systems and industrial ultra-pure/high purity water.18
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Ralstonia (named after the American bacteriologist corynebacteria, it has been reclassified.32 Infection
Original Articles E. Ralston) is a genus of Proteobacteria, previously due to L. aquatica is rare, and is commonly catheter
included in the genus Pseudomonas and contains 13 associated in immunocompromised patients. Serious
species (R. basilensis, R. campinensis, R. eutropha, R. infections in healthy people however, have also been
gilardii, R. insidiosa, R. mannitolilytica, R. metallidurans, reported.33
R. paucula,R. pickettii, R. respiraculi,R. solanacearum, 4.4. Brevundimonas aurantiaca and Pseudomonas
R. syzygii, R. taiwanensis). Most of these bacteria are aeruginosa
environmental bacteria with no clinical significance. Out of the 90 samples 34 (37.8%) showed the
However some of the species like Ralstonia pickettii presence of Brevundimonas aurantiaca. This bacteria
can cause bacteraemia and serious infections e.g. was present in water from all sources except the MWS.
sepsis contaminating injection solutions and aqueous The highest contamination rate was in DWB (50%).
chlorhexidine solutions.19 These bacteria were also The pattern of contamination was the same with
documented to be related to infection in cystic Pseudomonas aeruginosa, which was not present in
fibrosis patients.19 R. paucula and R. gilardii have only MWS and DWS, but present in 25% of the samples
been isolated from human clinical samples including taken from DWB, 8.3% ofH/S water samples and 8.3%
cerebrospinal fluid, bone marrow, wounds, and the of samples taken from WLT. The total number of samples
respiratory tract.21 Previous studies stated that the positive for Pseudomonas aeruginosa was 9 (10%).
majority of the Ralstonia isolates showed susceptibility Brevundimonas (Pseudomonas) aurantiaca is a
to most of the tested antibiotics.18 gram-negative soil bacterium which can synthesize
4.2. Sphingomonas paucimobilis antimicrobial compounds that have the same
The second most common contaminant of the structure of compounds produced by other members
MWS, DWSand dental units’ WLT was an aerobic of pseudomonades. These include phenazines,
bacterium found in soil and water known as proteins, phloroglucinols and Mycolytin (an antifungal
Sphingomonas paucimobilis. Although it rarely biopesticid).34 These bacteria showed remarkable
causes infection it has been reported as a causative intrapopulation phenotypic variability observed
agent of healthcare-associated infection especially in during their germination. This is an important
immunocompromised patients. In the current study it survival strategy under unfavorable environmental
was found in 88.8% of the collected samples. These conditions.35
findings are similar to previous studies.22,23 Pseudomonas aeruginosa is a gram-negative bacteria
Sphingomonas paucimobilis was reported that is citrate, catalase and oxidase positive. It has the
to cause outbreaks of bacteremia among ability to grow in plumping fixtures and survive in
immunocompromised patients in hematology and distilled water.36
oncology units due to bacterial contamination of Pseudomonas aeruginosa in samples taken from
hospital water systems.24 It is now emerging as an DWB, WLT or H/S need not infer an oral source of the
opportunistic pathogen that is frequently reported bacteria. In this study, Pseudomonas aeruginosa was
in clinical settings.25 It can be isolated from hospital present in 8.3% of H/S water samples which represent
environments such as distilled water, nebulizers, and the point of contact to the oral cavity. This, compared
multiple equipments used in medical care. It has been to the 25% of DWB samples suggests that back-flow of
associated with a few cases of continuous ambulatory the concerned bacteria from the oral cavity is unlikely.
peritoneal dialysis and is notorious for its resistance to Therefore, we can only assume but not confirm the
the commonly used antibiotics.26 Some reports stated presence of fairly effective mechanisms that prevent
that S. paucimobilis can cause infections in healthy sucking back fluids from patients’ oral cavities, and
as well as immunocompromised individuals where subsequent multiplication in our university’s dental
infection caused by S. paucimobilis can lead to septic clinic units. This eliminates a potential source of cross
shock.27 Although this organism is a gram negative infections.
bacteria it lacks the lipopolysaccharide components Our investigation showed that there were no
in the outer membrane of the cell wall which is bacteria of Streptococcus and Staphylococcus
associated with endotoxin activity.28 genera. Nevertheless, the presence of these
A recent study showed that S. paucimobilis isolates microorganisms in distilled water reservoir of dental
from cancer patients were fairly sensitive strains, units has been reported.37
with resistance observed only against ceftazidime
and aztreonam.14 This organism tends to show 5. Conclusion
unpredictable antibiotic sensitivity attributed to the The bacterial concentration in majority of the collected
antibiotics’ therapeutic failure.26 water was relatively higher than the standard counts.
4.3. Leifsonia The study revealed that the bottled units contained
The third most common contaminant Leifsonia was significantly higher numbers of CFU and had more
found in 73.5% of the samples collected from the chances of contamination with serious bacteria. The
MWS, DWS and dental unit’s WLT. It is an aquatic bacterial flora in the water samples comprised of
bacterium typically found in environmental water bacteria characteristic for water supply systems and
habitats and is a usual finding in dental water lines as opportunistic pathogens, with no bacteria of the oral
shown in previous studies.29,30,31 cavity flora. Nevertheless, microbial counts of water
This bacterium is catalase and oxidase positive. samples collected from dental units after replacement
L. aquatica was once classified as a species of the of all bottled dental units (causing the major
Corynebacterium genus. However, because of the contamination) demonstrated substantial reduction
chemotaxonomic and genetic differences from in the counts. In addition, this study's determination
130 Stoma Edu J. 2017;4(2): 126-132 http://www.stomaeduj.com
THE MICROBIAL PROFILES OF DENTAL UNIT WATERLINES IN A
DENTAL SCHOOL CLINIC
of contamination sources and evaluation of We thank the microbiology team at RAK College of
Original Articles
microbial load in RAKCODS could contribute to the Medical Sciences, RAK Medical and Health Sciences
development of quality control methods in the future. University. Special thanks goes to Prof. Tarek El-Etreby
and Dr. Mahmood Hachimfor their great support
Acknowledgments and Mr. Micheal Magaogao, the senior laboratory
The current study has been approved by the Research technician in the department for his tremendous
and Ethics Committee of Ras Alkhaimah Medical and efforts. This work was sponsored by RAK College of
Health Sciences University, 2015 (RAKMHSU-REC-3- Dental Sciences.
2015-UG-D).
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Stomatology Edu Journal 131
THE MICROBIAL PROFILES OF DENTAL UNIT WATERLINES IN A
DENTAL SCHOOL CLINIC
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Juma ALKHABULI
BDS, MDentSci, MFDS RCPS, FICD, PhD
Associate Professor and Chair of Basic and Medical Sciences Department
Ras Al-Khaimah (RAK) College of Dental Sciences
RAK Medical and Health Sciences University (RAKMHSU), UAE
CV
Dr Alkhabuli obtained BDS from University of Garyounis, Libya (1985). Between 1986-199, worked in health
sector in different regions, where he gained most of his clinical experience as a general practitioner. He was
appointed as director of Aujalah health center, head of regional Medical & Dental Association and director
of dental section of SIRTCO medical department. 2001-2005 obtained his MDS and PhD in oral pathology
from Leeds University, UK. MFDS RCPS (Glasgow), FICD (North Africa). His research interest is in role of
immunosurveillance cells in tumours and published several papers in this context. He worked as Associate
Professor in Ajman University, UAE in 2006. Joined RAK College of Dental Science in 2008 as Associate
Professor and contributed massively in its foundation and was the dean in charge between 2010 and 2011.
Questions
Presence of which of the following bacteria in a water sample suggests an oral source?
qa. Staphylococcus;
qb. Leifsonia;
qc. Pseudomonas aeruginosa;
qd. A and C.
The most commonly present bacteria in the main water source, distilled water source and
dental units’ water line tubes was:
qa. Leifsonia;
qb. Sphingomonas paucimobilis;
qc. Ralstonia spp.;
qd. A, B and C above.
Samples from which of the following sources met the CDC recommendations for non-surgical
dental water which have a heterotrophic count of ≤500 CFU/ml?
qa. Main Water Source samples;
qb. Distilled water source;
qc. Both A and B;
qd. None of the samples.
Which of the following statements is CORRECT?
qa. Non-bottled units contained significantly higher numbers of CFU compared to bottled units;
qb. Bottled units contained significantly higher numbers of CFU compared to non-bottled units;
qc. The difference in bacterial count between bottled and non-bottled units was not statistically significant;
qd. None of the statements is correct.
132 Stoma Edu J. 2017;4(2): 126-132 http://www.stomaeduj.com