Legionella pneumophila, the causative agent of Legionnaires' disease, is known to colonise and frequently grow in cooling tower waters. Disease is acquired by inhaling aerosol contaminated by legionellae. Determination of the count of Legionella pneumophila in cooling tower waters may, therefore, be useful for risk assessment. In our survey, 103 water samples from 50 cooling towers were examined over a five-year period to indicate the seasonal distribution and the ecology of L. pneumophila, as regards temperature and pH. L. pneumophila serogroup 1 was found in 44% of the isolated strains, which is primarily responsible for the majority of Legionnaires' disease. The large majority of examined towers had levels of L. pneumophila in the high-risk category. These cooling towers have been linked to many outbreaks of Legionnaires' disease.

The presence of microbial cells on surfaces results in the formation of biofilms, which may also give rise to microbiologically influenced corrosion. Biofilms accumulate on all submerged industrial and environmental surfaces. The efficacy of disinfectants is usually evaluated using planktonic cultures, which often leads to an underestimate of the concentration required to control a biofilm. The aim of this study was to investigate the efficacy of monochloramine on biofilms developed in a cooling tower. The disinfectants selected for the study were commercial formulations recommended for controlling microbial growth in cooling towers. A cooling tower and a laboratory model recirculating water system were used as biofilm reactors. Although previous studies have evaluated the efficacy of free chlorine and monochloramine for controlling biofilm growth, there is a lack of published data concerning the use monochloramine in cooling towers. Stainless steel coupons were inserted in each tower basin for a period of 30 d before removal. Monochloramine and free chlorine were tested under identical conditions on mixed biofilms which had been allowed to grow on coupons. Monochloramine was found to be significantly more effective than free chlorine against cooling tower biofilms.

This study was implemented to determine the environmental factors and causative organisms of the recent mucilage formation in the Marmara Sea. Samples were taken during the study from 7 different depths (0.5–30 m) of one sampling point of the Büyükada Island shore between January and June 2008. As a result, 62 phytoplankton species belonging to 5 different groups were identified. Dinoflagellates were dominant in terms of species number, and diatoms in terms of cell number. In January and February, mucilage formation was very dense, where 5 phytoplankton species (Clindrotheca closterium, Pseudo-nitzschiasp.,Skeletonema costatum, Thalassiosira rotula(Bacillariophyceae) andGonyaulax fragilis(Dinophyceae)) were reported as dominant organisms. Among them,Gonyaulax fragilishas never been reported in the Marmara Sea previously, thus that organism appeared firstly with the formation of dense mucilage and then when the mucilage decayed in May and June 2008,G. fragilisdisappeared. Autofluorescent single-celled organisms were classified in three groups depending on their cell sizes (>20 μm, >2 μm, >0.2 μm) by membrane filtration and total count of bacteria were determined by epifluorescence microscope after dying with DAPI. The highest total bacteria was recorded in April at 25 m depth (6655 ± 44.4 cells ml−1) while the lowest count was in June at 0.5 m depth (1077 ± 26.1 cells ml−1). The seawater temperature ranged between 7.0 and 21.5°C, salinity between 20.9 and 37.4 ppt and dissolved oxygen amount between 2.75 and 12.75 mg l−1. The chlorophyll-aamount ranged between 0.10 and 6.35 μg l−1, the higher values were recorded in January at 15 m depth (6.35 μg l−1) and in April at 10 m depth (4.89 μg l−1). Among the nutrients, the amounts of nitrite + nitrate-N varied between 0.02 and 7.67 μg-at N l−1, phosphate-P between 0.11 and 0.96 μg-at P l−1and silicate-Si between 0.37 and 8.93 μg-at Si l−1. The highest values were determined at a deeper layer where nutrients are accumulated. On the other hand, the N:P ratio interval was found as 0.1–11.3, Si:P ratio as 2.92–52.33 and N:Si ratio as 0.01–1.10 during the sampling period. Nitrogen was the limiting nutrient and the silica amount was enough to enable the development of diatoms.

-The aim of the study was to evaluate the response of two different Legionella pneumophila strains with their 20 times subcultured passages, regarding VBNC induction and to test the effect of multiple subculturing on cell vulnerability in the presence of monochloramine. A freshly opened of L. pneumophila ATCC 33152, a first subculture of environmental isolate of L. pneumophila and the 20 th subcultures of both strains were tested for survival in the presence of different doses of monochloramine (24 hours). Besides culture method, live-dead cells were visualised. It was found that multiple subcultured strains were significantly more susceptible to monochloramine and not capable of entering to VBNC state in comparison with freshly opened/isolated strains. Environmental isolate was survived at 2 ppm dose of monochloramine after 24 h, whereas 20 th subculture of this strain failed to survive. Multiple subcultured L. pneumophila strains were lost their culturability and viability significantly. This phenomenon should be considered while working with laboratory strains. After monochloramine disinfection, L. pneumophila bacteria can completely lose their cultivability but do not lose viability, which remains responsible for serious outbreaks worldwide. Even after completely loosing cultivability, it is possible to find live cells in network water in the VBNC state.

Cooling towers have the potential to develop infectious concentrations of Legionella pneumophila. Legionella counts increases where biofilm and warm water temperatures are present. In this study, biofilm associated L. pneumophila and heterotrophic bacteria were compared in terms of material dependence. Model cooling tower system was experimentally infected by L. pneumophila standard strain and monthly monitored. Different materials were tested for a period of 180 days. The lowest L. pneumophila and heterotrophic plate counts were measured on plastic polymers, whereas L. pneumophila and heterotrophic bacteria were accumulated rapidly on galvanized steel surfaces. It can be concluded that selection of plastic polymers, as a manufacturing material, are suitable for recirculating water systems.