Cell surface hydrophobicity contributes to Lactobacillus tolerance to antibacterial actions of catechins

Although most Gram-positive bacteria are sensitive to epigallocatechin gallate (EGCg), some species of lactic acid bacteria (LAB) are highly tolerant. The mechanism of LAB tolerance to the antibacterial action of EGCg was investigated. LAB strains with three different cell wall composition types were used: Lactobacillus plantarum NBRC15891 (meso-DAP-type), Lactobacillus fermentum NBRC15885 (Orn-type), and Lactobacillus delbrueckii NBRC3073 (Lys-type). The minimum inhibitory concentration of EGCg for L. plantarum NBRC15891, L. fermentum NBRC15885, and L. delbrueckii NBRC3073 were >1000, >1000, and 500 μg/mL at pH 6.5, respectively. The cell surface hydrophobicity (CSH), and contents of extracellular polymeric substances (EPS) and teichoic acid of these strains suggested that strains with low CSH and producing greater amounts of EPS are highly resistant to EGCg at pH 6.5. After EGCg treatment, the membrane potential decreased in strains with high susceptibility to EGCg. Our findings suggested that LAB characterized by high EPS level and low CSH are resistant to EGCg at pH 6.5.