Antimicrobial action of epsilon-poly-L-lysine

The antimicrobial spectrum of epsilon-poly-L-lysine (n = 25-30, epsilon-PL) was investigated by comparison with alpha-poly-L-lysine (n = 50, alpha-PL). epsilon-PL showed antimicrobial activity against Gram-positive and -negative bacteria at concentrations of 1-8 micrograms/ml. alpha-PL was less active than epsilon-PL. A chain length of at least 10 L-lysine monomers was found to be optimum for antimicrobial activity. Chemical modification of the amino groups of epsilon-PL lowered its antibacterial activity. Studies on the mode of action of epsilon-PL suggest that absorption of epsilon-PL to the bacterial cell surface plays an important role in its antibacterial activity.