Antibacterial activity of lactic acid bacteria

Antagonističko djelovanje prema nepoželjnim i patogenim mikroorganizmima je poželjno svojstvo starter kultura i probiotičkih sojeva bakterija mliječne kiseline (BMK). Za njihovu industrijsku primjenu potrebno ih je prirediti u koncentriranom obliku, kao liofilizirane ili koncentrirane zamrznute kulture. Stoga je u ovom radu praćeno preživljavanje triju probiotičkih sojeva Lactobacillus helveticus M92, Lactobacillus plantarum L4 i Enterococcus faecium L3 tijekom liofilizacije i čuvanja pri različitim temperaturama kao svježih koncentriranih kultura, a provedeno je i ispitivanje njihove antibakterijske aktivnosti metodom difuzije u agar i turbidimetrijskom metodom prema test mikroorganizmima: Staphylococcus aureus 3048, Staphylococcus aureus K-144, Escherichia coli 3014, Salmonella enterica serovar Typhimurium, Bacillus subtilis ATCC 6633 i Bacillus cereus. Ispitana je također i bakteriocinska aktivnost triju probiotičkih sojeva koja je usmjerena prvenstveno prema srodnim bakterijskim vrstama, metodom s dvostrukim slojem agara. Kako su bakteriocini proteinske supstancije, provedeno je taloženje proteina iz supernatanata kultura s (NH4)2SO4. Dobiveni rezultati ukazuju na potencijalnu bakteriocinsku aktivnost ispitivanih probiotičkih sojeva.The antagonistic activity against undesirable and pathogen microorganisms is desirable property of starter cultures and probiotic strains of lactic acid bacteria (LAB). For their industrial application, these bacteria must be prepared in concentrated form, as freeze drayed or concentrated freezed cultures. Hence, the aim was to investigate the viability of three different probiotic strains Lactobacillus helveticus M92, Lactobacillus plantarum L4 i Enterococcus faecium L3 during the freeze-drying and storage of the concentrated cultures at different temperatures. The investigation of their antibacterial activity, against selected test microorganisms: Staphylococcus aureus 3048, Staphylococcus aureus K-144, Escherichia coli 3014, Salmonella enterica serovar Typhimurium, Bacillus subtilis ATCC 6633 and Bacillus cereus was examined, by agar well diffusion assay and turbidimetric assay. The ability of three probiotic strains to produce bacteriocins that are active firstly towards representatives of the same bacterial species was investigated by agar spot assay. As bacteriocins are proteinaceous substances, the precipitation of proteins from supernatants with (NH4)2SO4 was undertaken. The obtained results have shown potential bacteriocin activity of examined probiotic strains