Characterization of the substance inhibiting Staphylococcus aureus produced by a Lactobacillus sp.

초록

Lactobacilli have been considered to play important roles in the health of human. They secrete inhibitory substance to prevent infection by pathogenic organism. In a previous study we have newly isolated 105 strains of Lactobacillus spp. from human samples. In this study, using the plate diffusion method 7 strains showing antagonistic activity against pathogenic Staphylococcus aureus were selected among them. One strain which had shown the highest level of antimicrobial activity was identified as L. rhamonosus (KLB #298) by 16 rDNA sequencing. In mixed culture experiments growth of S. aureus was inhibited by KLB #298 at the early stationary phase when the culture pH dropped to 4.5. To characterize the antimicrobial activity cell-free culture supernatant was treated with catalase, lipase, -amylase and various proteases (pepsin, proteinase K, trypsin, -chymotrypsin), none of which inactivated the inhibitory activity of the supernatant. Therefore, it is likely that the inhibitory substance of KLB 298 is organic acid by which the culture becomes acidic so that S. aureus is inhibited. In addition, as H2O2 produced by lactobacilli has been suggested to be antimicrobial substance we have examined the correlation between H2O2 production and antagonistic activity. From qualitative analysis there seems to be a correlation between H2O2 production and antagonistic activity of KLB 298. However, further studies are needed to clearly show the relationship between H2O2 production and antagonistic activity in other lactobacilli.