Isolation of lactic acid bacteria and determination of antimicrobial and antibiofilm effects on food pathogens

ISOLATİON OF ANTİMİCROBİAL LACTİC ACİD BACTERİA AND DETERMİNATİON OF ANTİBİOFİLM EFFECTS ON FOOD PATHOGENS The purpose of this study is to investigate antibacterial, antibiofilm effects and antibiotic resistance of lactic acid bacteria (LAB) isolated from home-fermented milk and meat products. The identification of the isolates was performed with MALDITOF-MS and 16S rDNA gene sequencing. LAB cultures were isolated from different food products produced by traditional methods without using starter cultures. The gram-positive, catalase and oxidase negative cocci and bacilli strains were selected by examining the colony morphology, catalase, oxidase reaction and gram staining. The antimicrobial and antibiofilm effects of LAB's cell-free supernatants on Staphylococcus aureus (ATCC 25923), Listeria monocytogenes (ATCC 13932), Escherichia coli (ATCC 29998) and Bacillus cereus (ATCC 11778) were determined by agar well diffusion and microplate methods, respectively. The resistance of the isolates to six different antibiotics was determined by disk diffusion method. As a result, 7 out of 27 LAB isolates exhibited inhibition zones ranging from 8 to 11 mm against L. monocytogenes, and 8 to 10 mm against B. cereus, while they did not show antibacterial activity against S.aureus and E.coli. Six isolates (I-3, I-5, I-6, I-21, I-34 and I-36) showed antibiofilm activity against S. aureus, L. monocytogenes, E. coli at rates ranging from 85% to 100% except I-20. It was found that all seven isolates were sensitive to Chloramphenicol (30 µg) and Ampicillin (10 µg), as well as, moderately sensitive to Gentamicin (120µg). A 42.85% of the isolates were resistant to Sulfamethoxazole (25µg) and 71.42% of the isolates were resistant to Ciprofloxacin (5 µg) and Oxacillin (1µg). The six LAB which have both antimicrobial and antibiofilm effects were identified using 16S rDNA gene sequencing. I-3, I-21 and I-36 were identified as Pediococcus pentosaceus, while I-5, I-6 and I-34 were identified as Lactiplantibacillus plantarum with 100% similarity to the reference sequence.