Investigation of antibacterial, antibiofilm and anti-quorum sensing activities of Lactobacillus sp. isolated from raw milk and cheese samples

Investigation of Antibacterial, Antibiofilm, and Anti-Quorum Sensing Activities of the Lactobacillus sp. Isolated from Raw Milk and Cheese Samples Lactobacilli produce compounds with various biological activities and potential to be used in pharmaceutical product development. In this study, 52 Lactobacillus sp., which were isolated from 23 different raw cow's milk and 23 different cheese samples, were used. The antibacterial, antibiofilm, and anti-quorum sensing(anti-QS) activities of the supernatants of the isolates, identified by MALDI-TOF MS, were investigated and the DL-p-hydroxyphenyllactic acid, ferulic acid, hydrogen peroxide, and acetic acid compounds in the supernatants were determined by HPLC-UV/DAD method. Among the isolates, 22 were identified as Lacticaseibacillus casei/paracasei/rhamnosus,14 as Lactiplantibacillus pentosus/plantarum/paraplantarum,5 as Levilactobacillus brevis, 3 as Lentilactobacillusparabuchneri, 3 as Latilactobacillus curvatus, 3 as Loigolactobacillus coryniformis and 2 as Limosilactobacillus fermentum. The supernatants of 10 L. pentosus/plantarum/paraplantarum and 9 L. casei/paracasei/rhamnosus exhibited antibacterial activity against Pseudomonas aeruginosa. Additionally, the supernatants of 3 L. casei/paracasei/rhamnosus isolatesshowed antibacterial activity against Escherichia. coli, and 1 L. casei/paracasei/rhamnosus isolate exhibited antibacterial activity against Klebsiella pneumoniae.The antibacterial activity of supernatant 3b (L. casei/paracasei/rhamnosus), which contained the highest amount of hydrogen peroxide, acetic acid, and ferulic acid, was not observedagainst any of the tested bacteria. This suggests that the antibacterial activity observed may not be directly attributed to the quantified compounds. Regarding antibiofilm activity, the isolates with the highest inhibition values in their supernatants were 20b (L. corynformis ssp. coryniformis) with 83.84% inhibition, 18d (L. casei/paracasei/rhamnosus) with 83.38% inhibition, and 18a (L. fermentum) with 80.13% inhibition. Notably, supernatant 13a (L. parabuchneri), which exhibited high biofilm inhibition, had the lowest hydrogen peroxide and acetic acid levels among the isolates and did not contain ferulic acid. This suggests that the observed activity may not be directly linked to these compounds. Our study determined that all bacterial supernatants except the isolate supernatants 2b (L. parabuchneri) and 13a (L. parabuchneri) showed anti-QS activity by forming the violacein inhibition zone. The fact that these two isolates, which did not show any anti-QS activity, did not show similarity in terms of the compounds that were quantified suggested that the anti-QS activity observed could not be directly associated with these compounds. Keywords: Antibacterial activity, Antibiofilm activity, Anti-quorum sensing activity,HPLC-UV/DAD, Lactobacillus sp.