EXAMINATION OF THE CAPABILITIES OF ATTACHMENT AND BIOFILM FORMATION OF DIFFERENT Listeria monocytogenes STRAINS

Listeria monocytogene is the causative agent of a severe illness in humans and animals and food is the main route of infection. Some L. mnocytogenes strains persist on the surface of working areas in food plants for several months or years, so the equipment becomes the source of secondary contamination. Among other things, the persistence is associated with the ability to form a biofilm, alone or in a community with other bacterial species usually present in food industry. Biofilms present long lasting contamination sources, and bacteria in the biofilm express increased resistance to the effect of disinfectants. All materials usually used in food industry, such as stainless steel, aluminum, glass, rubber, fluored polymer, nylon, teflon, may be a substrate for the development of bacterial biofilm. The objective of this work was to examine the capabilities of 14 L. monocytogenes strains of different origin to attach and to form biofilm on glass surface. The strains originated from animals (8 strains), food (4 strains) and feed (1 strain). The referent strain was a human isolate (ATCC 19115). The number of L. monocytogenes was determined after three hours of attachment at 5 o C, 25 o C and 37 o C and after 48-hour incubation in tryptone soy broth by the use of standard count technique on blood agar from tenfold dilution. Three days old biofilm of the selected L. monocytogenes strains was examined by scanning electron microscopy (SEM) and treated with disinfectants (Peral-S and Environ-4) for 5 and 10 minutes. For all the examined L. monocytogenes strains the number of attached bacteria to glass slides for 3 hours of incubation in static conditions at 25 o C and 37 o C ranged from 10 2 -10 4 cfu/cm 2 . After three hours of incubation at 5 o C bacteria did not attach to glass slides. After 48 h of incubation the number of cells that grow on glass slides did not depend on initial attachment and for all the strains it was 10 5 -10 7 cfu/cm 2 . Scanning electron microscopy confirmed the ability of tested strains to attach on glass surface. L. monocytogenes cells attached to glass surface expressed higher resistance to disinfectants that the cells in suspension.