The aim of this study was to evaluate the bacterial contamination level and to determine the antibiotic susceptibility of the isolated bacteria from dental unit waterlines (DUWLs) in Istanbul. Bacterial quality of DUWLs is very important, as patients and dental staff are regularly exposed to water and aerosols generated by the unit. If opportunistic pathogens such as Staphylococcus aureus, Pseudomonas aeruginosa, and Legionella pneumophila are present in DUWLs, patient and dental staff can be infected. One hundred water samples were collected from high-speed drills and input waters from 50 dental units. Aerobic heterotrophic bacteria counts and the presence of Legionella, Pseudomonas, oral streptococci, and Staphylococcus were investigated in dental unit waters and aerosol samples. In addition, the antibiotic susceptibility of the isolated and identified bacteria from DUWLs was examined. This research found that 37 out of 50 dental unit water samples exceeded the American Dental Association's limit of 200 colony-forming units (CFU)/mL(-1). Legionella, oral streptococci, and S. aureus were not detected in any water or aerosol samples, but P. aeruginosa was isolated in three DUWLs. Also, Pseudomonas and Staphylococcus were found in water and aerosol samples. Cefoperazone, ofloxacin, gentamicin, ciprofloxacin, and piperacillin were the most effective antibiotics against the isolated bacteria from DUWLs.

The corrosion behaviour of galvanized steel in cooling tower water containing a biocide and a corrosion inhibitor was investigated over a 10-month period in a hotel. Planktonic and sessile numbers of sulphate reducing bacteria (SRB) and heterotrophic bacteria were monitored. The corrosion rate was determined by the weight loss method. The corrosion products were analyzed by energy dispersive X-ray spectroscopy and X-ray diffraction. A mineralized, heterogeneous biofilm was observed on the coupons. Although a biocide and a corrosion inhibitor were regularly added to the cooling water, the results showed that microorganisms, such as SRB in the mixed species biofilm, caused corrosion of galvanized steel. It was observed that Zn layers on the test coupons were completely depleted after 3 months. The Fe concentrations in the biofilm showed significant correlations with the weight loss and carbohydrate concentration (respectively, p < 0.01 and p < 0.01).

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The microorganisms living in the cooling towers water can affect both human health through inhalation of aerosolized water as well as industrial processes. In order to analyse such man-made water systems, microbiological tests that can give results in a short time are needed. In this study, the presence of heterotrophic bacteria, Legionella bacteria and free-living amoeba, FLA, including Acanthamoeba, in cooling-tower water and biofilm samples were investigated using two different methods, fluorescent in situ hybridization (FISH), and culture. For this, a total of 40 water and biofilm samples were taken from 16 different cooling towers in Istanbul. FISH and culture analysis have revealed that the number of heterotrophic bacteria within the water and the biofilm samples was above the threshold values (>10 5 cell. mL-1), generally. Despite Acanthamoeba were present in all cooling tower specimens, Legionella pneumophila serogroup 1 were only detected in the biofilm of one cooling tower. According to the results of this study, both methods are recommended to be used in conjunction. Due to the the large biodiversity of FLA such as Hartmanella sp. and Naeglaria sp, there is a need for new studies utilizing FISH method for sensitive, reliable results in a short period of time.