Ayşın Çotuk

The effect of the coelomic fluid of the earthworm Eisenia foetida Sav. on certain bacteria and the role of the coelomocytes in internal defence

Abstract 1. 1. Bacteria have been isolated from the coelomic fluid and medium of Eisenia foetida and the effect of the coelomic fluid on them assayed. 2. 2. While a normal complement of coelomocytes appeared essential in preventing growth of bacteria, cell-free fluid inhibited some of the strains isolated, but most were not affected. 3. 3. Injection of various strains into the coelomic cavity demonstrated that large numbers of A. hydrophila and S. marcescens lead to septicaemia and death but that low numbers (3 × 10 6 ) were not pathogenic providing coelomocytes were present. 4. 4. B. thuringiensis (Heimpel EN-1) did not appear to be pathogenic to E. foetida . 5. 5. Injection of vaccines of formalized A. hydrophila and B. thuringiensis failed to induce lytic activity in the fluid.

The corrosion behaviour of galvanized steel in cooling tower water containing a biocide and a corrosion inhibitor

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).

Pioneer colonizer microorganisms in biofilm formation on galvanized steel in a simulated recirculating cooling-water system

Some bacteria have a higher tendency to produce biofilm than others. Especially, Pseudomonas and Aeromonas strains are acknowledged to be pioneer colonizers and are predominant in biofilm formation. We examined biofilm formation and first attachment maintance of biofilms of Pseudomonas spp., Pseudomonas aeruginosa, Aeromonas spp, sulphate reducing bacteria and filamentous fungi. A simulated recirculating cooling‐water system was used. Heterotrophic bacteria counts on galvanized steel and glass surfaces rose during the tidy period of 720 hours. In addition, we determined that although Pseudomonas spp., Pseudomonas aeruginosa and Aeromonas spp. were the pioneer colonizers, they surprisingly could not be determined in the biofilms on both types of surface after 456 hours. Sulphate reducing bacteria were observed in biofilms on both surfaces from the outset of the experiments. Filamentous fungi were seen on the galvanized steel and glass surfaces after 0.5 h. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

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

Efficacy of Gemacide PN-50TM (a quaternary ammonium compound) as a commercial formulation recommended for disinfecting heat exchangers was determined for both planktonic and sessile populations of variousLegionella pneumophila strains. The quaternary ammonium compound (QAC) was preferred as an alternative due to the emerging resistance of potentially pathogenic bacteria against different biocides. PlanktonicL. 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 ofL. pneumophila strains to the biocide was different. The biocide was found effective below recommended dosages (1000–2000 mg/L) against planktonic populations ofL. 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 ofL. 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.

Effects of short-time drying on biofilm-associated bacteria

Microorganisms tend to form biofilms consisting of cells embedded in a highly hydrated extracellular polymeric matrix. The biofilm protects its inhabitants from antimicrobial agents, pH alterations, and confers protection against drying. It is known that biofilm-associated bacteria can survive for a while in the absence of water. When rehydrated, metabolic processes are quickly restored and microorganisms resume life. The aim of this study is to evaluate the survival of heterotrophic bacteria, sulphate-reducing bacteria and amoeba against short-time drying. Biofilms were allowed to grow for 30 and 60 days on stainless steel (316, 2B) coupons in annular biofilm reactor, which was fed with drinking water network under constant, non-turbulent shear stress and temperature. The results presented in this study indicate a role for biofilm layer in protecting biofilm-associated microorganisms from drying. The current study has provided that short-time (24 h) absence of water could not affect biofilm-associated heterotrophic microorganisms significantly, in terms of cell viability.