Süt işletmelerinde biyofilm oluşturan mikroorganizmalar ve biyofilm oluşumunun karakterizasyonu

Abstract

Biofilm formation is a common problem in various food industries especially in dairy industry. There are very limited studies about the biofilm forming microorganisms on the surfaces of dairy plants, surface properties of biofilm forming microorganisms, biofilm formation mechanism in dairy industry, gaining permanency of biofilm formation and prevent or eliminate of biofilm formation. In this study, microbiological samples were taken from different sampling surfaces in a dairy plant in Ankara. Totally 495 microorganism isolates including bacteria and yeasts were isolated from these surfaces and then these isolates were identified. Isolates were identified according to the morphological, physiological and biochemical properties, and 16S rRNA gene sequence analysis. Among the isolates, totally 10 isolates were chosen, which have biofilm forming potential on the surfaces. The selected microorganisms were Pseudomonas aeruginosa, Enterococcus feacalis, Staphylococcus epidermidis, Lactococcus garvieae, Bacillus toyonensis, Escherichia coli, Klebsiella varriicola, Candida parapsilosis and Proteus mirabilis. Surface properties and exopolysaccharide production ability of these selected microorganisms were investigated. Among the isolates with high surface properties and high exopolysaccharide production ability, Bacillus toyonensis and Pseudomonas aeruginosa were selected for representing of Gram positive and Gram negative bacterial isolates, respectively. Surface properties and exopolysaccharide production ability of P. aeruginosa were generally higher than those of B. toyonensis. Biofilm forming potential of these test microorganisms was investigated by using stainless steel plates in the model systems of “batch” and “flow” growth media. Pseudomonas aeruginosa had higher adhesion and biofilm forming ability in both batch and flow growth media than those of Bacillus toyonensis. These results indicated that the cell wall characteristics of Gram negative bacteria may have a certain efficacy on the adhesion of these bacteria to the stainless steel plates in the model systems. It was determined that waiting temperatures may be effective on the adhesion and biofilm forming ability of the test microorganisms in both batch and flow growth media. Especially waiting at low temperatures such as at 5 oC may prevent adhesion and biofilm formation of microorganisms. However, this effect may change according to the kind of microorganism and its individual characteristics. These results pointed out that adhesion and biofilm forming ability of microorganisms may change depending on whether the growth medium is batch or flow. Stainless steel test plates were subjected to cleaning/disinfection treatments in batch and flow growth media with 3 and 5 times, respectively. Cultural counting methods indicated that bacterial cell adhesion was carried out on the test surfaces during the successive cleaning/disinfection treatments but there was no biofilm formation. It was determined that certain numbers of bacterial cells were adhered to the test surfaces in batch and flow growth media but these adhered bacterial cells were wholly removed from the test surfaces by cleaning/disinfection treatments. SEM and fluorescence microscopes appearances and profilometer measuring results confirmed above results. Adhesion of bacterial cells on surfaces of stainless steel test plates in batch and flow growth media could be explained as “initial phase of biofilm formation”. It was thought that there was big effect of the surface active agent (P3-Topax) and nitric acid used in the dairy plant in the wholly removing of bacterial cells from the test surface. It is necessary to keep the test surfaces in the batch or flow growth media with many successive repetitious. Many years are necessary to observe the biofilm formation in the batch or flow growth media in dairy plants after the bacterial cell adhesions. Prevention of biofilm formation on the surfaces of dairy plants should be taken into consideration preferably. Supplying good and high qualified raw materials to the dairy plants, following and controlling of biofilm formation on the surfaces continuously, taking effective hygiene and sanitation preventing measures on the microorganisms having high biofilm formation ability, making suitable and effective changes on these hygiene and sanitation preventing measures are the basic applications for prevent the biofilm formations.