Investigation of biofilm formation by Listeria spp. isolated from raw milk and cheese samples

In this study, existence of Listeria species was investigated in 80 raw milk and 80 cheese samples which were presented to consumption in Ankara. For this purpose, samples were collected at sterile conditions, brought to the laborotary immediately and analysed at same day. Listeria species were isolated from the samples according to ISO 11290-1/A1-2004 method. 15 Listeria isolates obtained from collected 80 raw milk and 80 cheese samples. 11 of these isolates were identified as Listeria innocua, 3 of them were identified as Listeria grayi and 1 of them was identified as Listeria welshimeri. At biofilm study, widely used standard microplate (96-welled plastic microplate) technique was used. In this study; tyriptic soya broth (TSB), TSB+1% NaCl, TSB+1% glucose media were inoculated with Listeria spp. and incubated at 30°C for 24, 48 and 72 hours. Out of 15 Listeria isolates 9 isolates from raw milk and cheese samples were determined to show tight attachment after 24 hours 5 isolates after 48 hours, 1 isolate after 72 hours at 30°C. 5 isolates were determined to show tight attachment after 24 hours, 4 isolates after 48 hours, 2 isolates after 72 hours at 30°C in TSB+1% NaCl medium. 3 isolates were determined to show tight vii attachment after 24 hours, 6 isolates after 48 hours and 1 isolate after 72 hours at 30°C in TSB+1% glucose medium. In TSB medium, isolate number 5 L. innocua?s attachment isolated from raw milk samples were evaluated 1.016 while isolate number 15 L. grayi?s attachment isolated from cheese samples were evaluated at maximum value of 1.101 at 30°C after 24 hours. In TSB+1% NaCl medium, isolate number 7 L. innocua?s attachment isolated from raw milk samples were evaluated 0.459 while isolate number 15 L. grayi?s attachment isolated from cheese samples were evaluated at maximum value of 0.617 at 30°C after 24 hours. In TSB+1% glucose medium, isolate number 7 L. innocua?s attachment isolated from raw milk samples were evaluated 0.253 while isolate number 11 L. grayi?s attachment isolated from cheese samples were evaluated at maximum value of 0.420 at 30°C after 24 hours. After 48 hours of incubation, the 15 Listeria isolates which were isolated from raw milk aand cheese showed a strong attachment to microtiter. After 48 hours of incubation the TSB+1% glucose medium was the best medium for attachment. This is because of the exopolysaccharide which is produced by bacteria during biofilm formation.