Antimicrobial activity of L. plantarum, isolated from a traditional lactic acid fermentation of table olives

Abstract

Lactobacillus plantarum strain LB17.2b, isolated from traditional table olive fermentation has been shown to produce thermostable antibacterial proteins. At pH 6.5, the proteinaceous fraction obtained from culture supernatant was active against Enterococcus faecalis and against natural competitors of L. plantarum from olive fermentation brines. Bioactivity was quantified against Weissella paramesenteroides DSM20288 using the critical dilution method by a regression procedure. This bioactivity has been found to be growth-associated indicating a primary metabolite kinetics. Ultrafiltration studies with supernatants from different fermentation times have been carried out. A two-fold increase in the activity of the retentate from the 30 kg·mol-1 cut-off membrane was observed, by comparison with the total activity applied to this membrane (culture supernatant). The addition of the filtrate to this retentate caused a marked drop in activity, most probably associated with the presence of an inhibitor. These studies also demonstrated the presence of another antibacterial proteinaceous compound showing a wider inhibitory spectrum and produced during culture stationary phase. In the presence of lactic acid (pH 3.7), these antimicrobial proteinaceous compounds have been found to inhibit Gram-negative human pathogens, probably by a synergistic effect. At the present time one bacteriocin-like compound was isolated, showing a molecular mass of approximately 50 kg·mol-1. The presence of another compound of different properties and with a molecular mass between 3 and 10 kg·mol-1 was also detected.