Distribution of Bacteria Causing Legionnaires Disease at Potable Water in İstanbul

Legionella pneumophila (especially L. pneumophila serogroup 1) known as causing Legionnaires' disease inhabits surface waters, such as rivers, lakes, and streams. Hence, these bacteria can easily infect man-made water systems. It is known that these bacteria cause various infections and even death in men. Therefore, to assess the role of potable water systems in buildings (especially hotels) around Istanbul as possible sources for Legionella infection, this study was performed during the period of 1996 to 2001. A total of 701 potable water samples (hot-cold water faucets and shower heads) collected from 162 buildings were concentrated by filtration, and inoculated onto buffered charcoal yeast extract agar (BCYE) added glycine, vancomycin, polymyxin, cycloheximide and incubated at 37degreesC for 14 days. Colonies consistent with Legionella morphology were subcultured to tryptone soy agar (TSA). Definitive identification was performed by latex agglutination (OXOID). The results were recorded as the highest number of confirmed Legionella (CFU/L). The water systems of 63 (38.8%) of the buildings tested were found to be positive for Legionella. It was found that 32 (24%) of the 134 strains determined as Legionella pneumophila were L. pneumophila serogroup 1; 102 strains (76%) were L. pneumophila serogroup 2-14. Generally, hot water circulating systems of buildings, such as hot water faucets and shower heads, were found to be the major sites for growth of L. pneumophila. According to the results, it is suggested that the large number of buildings (hotels) around Istanbul exhibit a low risk as a source of Legionnaires' disease

Isolation of a sulfide-producing bacterial consortium from cooling-tower water : Evaluation of corrosive effects on galvanized steel

Sulfidogenic Clostridia and sulfate reducing bacteria (SRB) often cohabit in nature. The presence of these microorganisms can cause microbially influenced corrosion (MIC) of materials in different ways. To investigate this aspect, bacteria were isolated from cooling tower water and used in corrosion tests of galvanized steel. The identity of the isolates was determined by comparative sequence analysis of PCR-amplified 16S rDNA gene fragments, separated by denaturing gradient gel electrophoresis (DGGE). This analysis showed that, in spite of the isolation process, colonies were not pure and consisted of a mixture of bacteria affiliated with Desulfosporosinus meridiei and Clostridium sp. To evaluate the corrosive effect, galvanized steel coupons were incubated with a mixed culture for 4, 8, 24, 72, 96, 168, 360 and 744 h, along with a control set in sterile culture medium only. The corrosion rate was determined by weight loss, and biofilm formation and corroded surfaces were observed by scanning electron microscopy (SEM). Although the sulfide-producing bacterial consortium led to a slight increase in the corrosion of galvanized steel coupons, when compared to the previous studies it can be said that Clostridium sp. can reduce the corrosive effect of the Desulfosporosinus sp. strain.</p

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

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