Microbial contamination of dental unit waterlines and effect on quality of indoor air

The microbiological quality in dental unit waterlines (DUWLs) is considered to be important because patients and dental staff with suppressed immune systems are regularly exposed to water and aerosols generated from dental units (DUs). Opportunistic pathogens like Pseudomonas, Legionella, Candida, and Aspergillus can be present in DUWLs, while during consultations, bioaerosols can be dispersed in the air, thus resulting in effects on microbiological quality of indoor air. This present study represents microbiological air and water quality in dental offices (DOs) and also concerns the relationship between the quality of DO air and dental unit water. This study aimed to assess both the microbial quality of dental unit water and the indoor air in 20 DOs and to survey the effect on the quality of the indoor air with the existing microorganisms in dental unit water. Fourteen out of 20 (70 %) DUWLs were found to be contaminated with a high number of aerobic mesophilic heterotrophic bacteria. In terms of bacterial air contamination levels, in 90 % of DOs, a medium level (< 500 colony-forming units (CFU)/m(3)) of contamination was determined, while in terms of microfungal air contamination, in all DOs, a low level (< 100 CFU/m(3)) of contamination was determined. Potential infection or allergen agents, such as Pseudomonas, Micrococcus, Staphylococcus, Alternaria, Cladosporium, Penicillium, Aspergillus, and Paecilomyces were isolated from water and air samples. This study's determination of contamination sources and evaluation of microbial load in DOs could contribute to the development of quality control methods in the future

Microbial corrosion of galvanized steel in a simulated recirculating cooling tower system

In this study, mixed species biofilm formation including sulphate reducing bacteria (SRB) on the galvanized steel surfaces and also microbiologically influenced corrosion (MIC) of galvanized steel were observed in a model recirculating cooling water system during 10 months. A biofilm which had a heterogeneous structure formed on galvanized steel coupons. The results suggested that galvanized steel was corroded by microorganisms as well as SRB in the biofilm. Extracellular carbohydrate was degraded and quantities of carbohydrate were positively correlated with the weight loss. The concentrations of zinc in the biofilm showed significant correlations with weight loss, carbohydrate amount and SRB count. (C) 2009 Elsevier Ltd. All rights reserved

The Effect of Desulfovibrio sp Biofilms on Corrosion Behavior of Copper in Sulfide-Containing Solutions

This study aims to detect the effect of Desulfovibrio sp. on copper in terms of biofilm formation and corrosion in 722 h. In that way, appropriate strategies to inhibit microbiological corrosion in copper systems with Desulfovibrio sp. can be evaluated. For this purpose, experiments were performed in 1 L glass model system containing 28 copper coupons and pure culture of the sulfate-reducing bacteria (SRB) strain Desulfovibrio sp. in Postgate's medium C. Also, a control system with copper coupons but without Desulfovibrio sp. containing sterile Postgate's medium was studied concurrently with the test system. The test coupons were collected from systems at certain time intervals, namely 24, 168, 360, and 720 h. The samples were then subjected to several characterization analyses such as measurement of Desulfovibrio sp. numbers, corrosion resistance, EPS extraction, carbohydrate analysis, SEM, and EDS. During the experiments, the maximum Desulfovibrio sp. count in biofilm samples was found at 360 h. Carbohydrate and copper concentrations in biofilm were increased over time. EDS analysis revealed Cu, S, C, O, and Cl peaks on the surface of the samples. For the control coupons, only Cu peaks were observed. The results obtained from this study showed that copper was corroded by Desulfovibrio sp. in the model system under laboratory conditions

Comparison of the microbial load of incoming and distal outlet waters from dental unit water systems in Istanbul

This is a cross-sectional study of the incoming and distal outlet water quality from 41 dental units in Istanbul, carried out to compare the total microbial loads using traditional culture method versus epifluorescence microscopy. The possible presence of Legionella pneumophila using traditional culture method was also analyzed. One hundred and twenty three samples were taken from the high-speed handpiece lines, air-water syringe lines and source (incoming) water supplies from 41 dental units. The samples were assayed for live/dead bacteria, heterotrophic bacterial counts and presence of L. pneumophila bacteria. Thirty nine out of 41 dental units (91%) were not able to meet the standard limit of 200 CFU/ml in dental unit waters. The live bacterial counts were 1-1.5 orders of magnitude higher than aerobic mesophilic heterotrophic bacteria. L. pneumophila (serogroup 2-14) was isolated from five out of 41 units. Some dental units were using commercially bottled (19 l) drinking water as a source. The source water of eight dental unit was heavily contaminated which were fed up by commercially bottled drinking water

Studies on the efficacy of Chloramine T trihydrate (N-chloro-p-toluene sulfonamide) against planktonic and sessile populations of different Legionella pneumophila strains

Effectiveness of Chloramine T trihydrate (N-chloro-p-toluene sulfonamide) on both planktonic and sessile populations of different Legionella pneumophila strains was assessed. Although Chloramine T is a recommended commercial formulation for disinfecting cooling towers, there is a lack of published data about the efficacy of this compound against both planktonic and sessile populations of L. pneumophila. Planktonic L. pneumophila strains were suspended in tap water and sessile L. pneumophila strains were grown on stainless steel which is used in the construction of cooling towers, followed by exposure to the biocide. The sensitivity of both planktonic and sessile populations of L. pneumophila strains was different. The biocide was found effective below recommended dosages (0.1-0.3%) against planktonic populations of L. pneumophila, whereas it was determined that higher dosages than those recommended were required for sessile populations of L. pneumophila. The results indicated that studying only the planktonic populations of L. pneumophila for biocide tests might not be sufficient to provide information about the optimum dosage and contact time. Therefore, efficacy has to be tested on both planktonic and sessile bacteria. (c) 2006 Elsevier GmbH. All rights reserved

OPPORTUNISTIC BACTERIAL PATHOGENS OF AEROSOL AND WATER SAMPLES FROM DENTAL EQUIPMENTS

Water and aerosol derived from high-powered aerosolizing instruments in dental units represents a potential source of bacterial infection especially by Legionella and Pseudomonas. In this study, water and aerosol samples were taken from 41 dental units in Istanbul. In the samples taken, the count of aerobic heterotrophic bacteria and the presence of Legionella and Pseudomonas were researched by using culture methods. The aerosol samples were collected by active sampling. Physical and chemical parameters of the samples were also measured. The number of aerobic heterotrophic bacteria in 26 dental units out of 41 (63. 41%) exceeded the acceptable limit. Gram negative rods were the predominant bacteria. Legionella spp. and Pseudomonas spp. were detected in one and eight water samples (19.5%), respectively. Pseudomonas was not detected in aerosols. The presence of Legionella in the aerosol taken from high-speed drills has been searched and detected for the first time in Turkey. These findings indicate that investigation on bacterial contamination and related risk factors in dentistry should be expanded and effective precautions should be applied in order to reduce bacterial loads

Efficacy of a quaternary ammonium compound against planktonic and sessile populations of different Legionella pneumophila strains

Efficacy of Gemacide PN-50(TM) (a quaternary ammonium compound) as a commercial formulation recommended for disinfecting heat exchangers was determined for both planktonic and sessile populations of various Legionella pneumophila strains. The quaternary ammonium compound (QAC) was preferred as an alternative due to the emerging resistance of potentially pathogenic bacteria against different biocides. Planktonic L. pneumophila strains were suspended in tap water while sessile ones were grown on stainless steel that is used in construction of the cooling towers, then both group of strains were exposed to the biocide. The sensitivity of both planktonic and sessile populations of L. pneumophila strains to the biocide was different. The biocide was found effective below recommended dosages (1000-2000 mg/L) against planktonic populations of L. pneumophila, whereas it was determined that higher than the recommended dosages were required for sessile populations. The environmental isolates were more resistant to the biocide than the ATCC isolate was. The results indicated that studying only the planktonic populations of L. pneumophila for biocide tests might not be sufficient to provide the optimum dosage and contact time information for field trials. Therefore, biocidal activity of a water treatment chemical must be evaluated in terms of dosage and contact times on both planktonic and sessile bacteria

Effect of Mixed-Species Biofilm on Copper Surfaces in Cooling Water System

This study aimed to investigate the formation and effect of a biofilm on copper heat exchangers in full-scale system conditions. A modified Pedersen device with copper coupons was installed in parallel to a heat exchanger system to investigate several physico-chemical parameters, such as bacterial enumeration, carbohydrate content of exopolymeric substances, weight loss of test/control coupons, Cu concentrations, and corrosion products over ten months. Findings of this study showed that planktonic bacterial cells attach to each other and form a mixed-species biofilm on the copper coupon surface even though copper is toxic to a variety of microorganisms. These results also revealed that the mixed-species biofilm has a corrosive effect on copper surfaces used in cooling water systems despite the presence of biocide and the corrosion inhibitor. Additionally, it was demonstrated that a shock-dosed biocide application increased the corrosion rate on copper surface in a real system. Preventing risk of microbiologically influenced corrosion entails appropriate material selection and proper/regular chemical treatment of cooling systems. The current study provides useful insights through the evaluation of corrosion of materials with microbiological techniques

Profiling of environmental Legionella pneumophila strains by randomly amplified polymorphic DNA method isolated from geographically nearby buildings

Legionella pneumophila (L. pneumophila) which is also known as etiologic agent Legionnaires Disease lives in natural water and man made water systems. These bacteria belonging to Legionellaceae family are divided 15 serogroups. Phenotypical methods used for the identification of Legionella isolates are not very discriminatory. In this study we investigated genotypic features of eight L. pneumophila serogroup 1 and 18 L. pneumophila serogroup 2-14 strains isolated from different buildings in Istanbul by randomly amplified polymorphic DNA (RAPD) method. Eight L. pneumophila serogroup 1 strains (37.5%) were similar RAPD profile and they were isolated from buildings located in a short distance (about 500 m). Four L. pneumophila serogroup 2-14 strains (22%) were identical genotypically. Three of these strains were isolated from buildings located in a short distance