Co-culture-inducible bacteriocin production in lactic acid bacteria

Svojstvo bakterija mliječne kiseline da inhibiraju rast drugih mikroorganizama rezultat je nastajanja i djelovanja organskih kiselina, prvenstveno mliječne i octene kiseline te posljedično niske pH vrijednosti okoliša, a mogu nastati i drugi metaboliti s antimikrobnom aktivnošću, kao što su vodikov peroksid, etanol, diacetil, acetaldehid i bakteriocini. Od svih navedenih spojeva, poseban se naglasak stavlja na bakteriocine, specifične peptide s antimikrobnim djelovanjem prema srodnim bakterijskim vrstama. Stoga je u ovom završnom radu provedeno ispitivanje prisutnosti gena koji kodiraju za plantaricine, odnosno enterocine kod sojeva BMK Lactobacillus brevis D6, Lactobacillus plantarum D13, Lactobacillus pentosus D1, Enterococcus durans D8 i Enterococcus faecium L3. Za daljnja ispitivanja bakteriocinskog djelovanja odabran je probiotički soj L. brevis D6. Budući da je bakteriocinska aktivnost usmjerena samo prema Gram-pozitivnim bakterijama kakve su i BMK, kao test-mikroorganizmi u tim ispitivanjima odabrane su dvije Gram-pozitivne bakterije koje se često pojavljuju kao kontaminanti u hrani - Staphylococcus aureus 3048 i Listeria monocytogenes ATCC 19111. Osim inhibitornog učinka probiotičkog soja L. brevis D6 na rast navedenih test-mikroorganizama, posebno je ispitana indukcija njegove bakteriocinogene aktivnosti uzgojem u kokultivaciji s istim test-mikroorganizmima.The ability of lactic acid bacteria to inhibit the growth of other microorganisms is the result of the formation of organic acids, primarily lactic and acetic acid and consequently low pH of the environment, as well as of the production of other metabolites with antimicrobial activity, such as hydrogen peroxide, ethanol, diacetyl, acetaldehyde and bacteriocins. Of all the above mentioned compounds, special emphasis is placed on bacteriocins, specific peptides with antimicrobial activity against related bacterial species. Therefore, in this Bachelor thesis, the presence of genes coding for plantaricis and enterocins in LAB strains Lactobacillus brevis D6, Lactobacillus plantarum D13, Lactobacillus pentosus D1, Enterococcus durans D8 and Enterococcus faecium L3 was examined. For further investigations of bacteriocins, probiotic strain L. brevis D6 was selected. Since activity of bacteriocins is directed only to Gram-positive bacteria such as LAB, two Gram-positive bacteria which are most common food contaminants are selected as test microorganisms - Staphylococcus aureus 3048 and Listeria monocytogenes ATCC 19111. In addition to the inhibitory effect of the probiotic strain L. brevis D6 on the growth of the above-mentioned test microorganisms, the induction of its bacteriocinogenic activity was studied by co-culturing with the same test microorganisms