Safety Issues of Lactobacillus bulgaricus with Respect to Human Gelatinases

Objectives: Probiotic therapy has been advocated for the prevention and treatment of a broad array of disorders. In oral medicine and dentistry probiotics have shown promising results in controlling dental diseases and yeast infections. However, before further recommendation, safety issues regarding the therapeutic use of living bacteria need to be carefully assessed. The aim of the present study was to investigate the gelatinolytic activity of 8 strains of Lactobacillus bulgaricus and their effects on human matrix metalloproteinase-9 (MMP-9). The hypothesis was that these bacteria used in yoghurt production for centuries are not proteolytic and thus can be safely used in the development of probiotic preparations. Methods: Bacterial cell fraction and supernatant specimens were prepared and studied with gelatin zymography and MMP-9 activation assessed by immunoblotting. The effect of synthetic MMP inhibitors and a serine protease inhibitor (Pefabloc) on bacterial proteinases was studied by zymography. Results: The results showed very low gelatinolytic activity. There was a slight difference between the supernatant and cell fractions so that the supernatant specimens produced weak gelatinolytic bands in zymography while hardly anything was seen in the cell fraction series. The tested synthetic MMP inhibitors and Pefabloc did not affect the proteolytic activity of the lactobacilli strains. Conclusions: The lactobacilli did not seem to induce the conversion of proMMP-9 to its active form. Consequently, our study hypothesis was confirmed and the studied Lactobacillus strains are not likely to induce degradation of the host tissue components.