2011 YÜksek lisans tez özetleri

Investigation Of Acylated Homoserine Lactone (Ahl) Molecule Production In Gram Negative Bacteria Isolated From Cooling Towers
Cooling towers are generally used to reduce the heat arised from factory, mall, hotel and hospital systems by the help of water. Cooling towers are continuously exposed to microorganisms because of their working with water and provide microorganisms a suitable habitat. Planktonic bacteria are usually attach to the surface that is eligible for them, start growing on that surface and form biofilm layer. There are multiple bacteria species in biofilm layers, therefore bacteria use cell to cell signalling systems to protect themselves from the environmental conditions and secure their species’ existance.

In this respect, in our study, water and biofilm samples from six different industrial plant’s cooling towers were collected and examined in view of fecal and total coliform bacteria, Pseudomonas aeruginosa, Aeromonas spp., and total heterotrophic bacteria and Gram negative rod bacteria were isolated.

Gram negative rod bacteria isolated from cooling tower water and biofilm samples which are important for human health, cooling tower and plant’s efficiency were examined for cell to cell signalling systems, N-acyl homoserine lactone (AHL) signal molecule types and biofilm formation capacity. Subsequently, bacteria isolated form cooling tower water and biofilm samples were examined for comparison of AHL signal molecule production characteristics. A. tumefaciens NT1 monitor strain is used for detection of long chained AHL signal molecules and C. violaceum CV026 monitor strain is used for detection of short chained AHL signal molecules. Crystal violet staining is used to detect the biofilm formation capacity of the bacteria isolated from water and biofilm samples.

The bacteriological analysis of six different plant’s cooling tower samples showed that all cooling towers have moderate and high risk factors according to European Working Group for Legionella Infections (EWGLI) criteria. Total of 99 Gram negative rod bacteria are isolated from cooling tower water and biofilm samples. 4 of 39 (10 %) strains isolated form water samples and 14 of 60 (23 %) strains isolated from biofilm samples are determined to be producing a variety of AHL signal molecules. In our study, it is determined that AHL signal molecule production ability of sessile bacteria is more than planktonic bacteria and there is a statistically significant difference between AHL signal molecule production of these two groups (p <0.05).

Furthermore, it is detected that bacteria belong to same species isolated from cooling tower water and biofilm samples produce different types of AHL signal molecules and that there are different types of AHL signal molecules in an AHL extract of a bacteria.

When biofilm formation capacity of these bacteria are examined, we find that bacteria isolated from cooling tower biofilm samples have moderate, and high biofilm formation capacity and bacteria isolated from cooling tower water samples have weak, and moderate biofilm formation capacity.

When statistical comparision of biofilm formation capacity of bacteria isolated from water and biofilm samples are made, it is determined that biofilm formation capacity of sessile bacteria is higher than planktonic bacteria (p <0.05).

ıt is determined that biofilm formation capacity of biofilm bacteria is statistically higher than those of planktonic bacteria (p <0.05).

Biofilm layer and planktonic bacteria present in cooling towers have very high importance for plant efficiency and public health. Therefore, it is very important to get rid of harmful pathogens. Understanding quorum sensing systems and it’s elements in bacteria will not only disrupt biofilm formation but also prevent them from undergo phenotypic changes, so that bacteria which can not develop resistance to antibacterial agents introduced to systems, could easily be removed from the cooling systems.