2011 YÜksek lisans tez özetleri

Investıgatıon Of Dıfferent Physıcal And Chemıcal Agents On Mıcrobıal Bıofılm Layer

Microorganisms which are living in water can adhere to the surfaces because of many different reasons and develop biofilm layers on surfaces. This layer can described as a ‘Bacterial community which adhering to live or dead surface by producing a polymeric matrix called extracellular polymeric substances (EPS)’. This EPS layer acts as cement for microorganisms for irreversible attachment to surfaces and can protect microorganisms from nutrient limitations, temperature and pH alteration biocides, toxins or short-term drying.

Biofilm can harbor variety of different genera, including Legionella. Particularly, the suitable water temperature range in cooling tower water favors the growth and survival of L. pneumophila in cooling tower and this microorganism can disseminated over a wide field through the aerosols which are produced by cooling tower fan. L. pneumophila is the most frequent cause of human legionellosis and a relatively common cause of community-acquired and nosocomial pneumonia in adults.

Besides cooling towers, surfaces that subject to biofilms are systems which include water as network water pipes, dental units, food producing equipments and some medical equipments. Some chemical and physical decontamination weak against methods are biofilm layer. EPS layer can protect microorganisms as a shield. Exchanges of environment’s temperature, pH and concentration sensed by biofilm microorganisms and bacteria become more achieve resistant trough genetic regulations. Furthermore, matrix can protect the bacteria through the medium of inhibit or delay disinfectant’s penetration to biofilm bacteria.

In our country, cooling towers are frequently used in some buildings such as hospitals, shopping centers, hotels. Disinfection is most widely used method for controlling microorganisms, but so far no reliable data was found about the effect of routine applications on biofilm microorganisms and L. pneumophila.

In this study, biofilm formation has been allowed for six month-period on glass microscope slides in a cooling tower water added model system which is experimentally infected by L. pneumophila ATCC 33152 and some cooling tower as primer inoculum. Coupons have been taken and analyzed after 24 hours exposition to different conditions of temperature, pH, concentration and different doses of disinfectants, and at the end of the 24 hours of exposure, effects of these parameters on aerobic heterotrophic bacteria and L. pneumophila are followed. Furthermore, number of live/dead microorganisms were analyzed by epifluorescence microscopy. Additionally, the biofilm amount on glass slides were analyzed quantitatively.

It has determined that biofilm layer can protect microorganisms from pH and temperature alterations, osmotic shock and shock disinfection. According to the results of culture and epifluorescence microscopy, it is revealed that microorganisms started to enter VBNC (viable but not culturable) phase.