In vitro antibacterial and hemolytic activities of crotamine, a small basic myotoxin from rattlesnake Crotalus durissus

Crotamine, a myotoxin from the venom of South American rattlesnake, is structurally related to beta-defensins, antimicrobial peptides (AMPs) found in vertebrate animals. Here, we tested the antibacterial properties of crotamine and found that it killed several strains of Escherichia coli, with the MICs ranging from 25 to 100 mu g ml(-1). Time-kill and bacterial membrane permeabilization assays revealed that killing of bacteria by crotamine occurred within 1 h and reached the maximum by 2 h. Additionally, the anti-E. coli activity of crotamine was completely abolished with 12.5 mM NaCl. Furthermore, the three intramolecular disulfide bonds of crotamine appeared dispensable for its antibacterial activity. The reduced form of crotamine was active against E. coli as well. However, crotamine showed no or weak activity up to 200 mu g ml(-1) against other species of Gram-negative and Gram-positive bacteria. Crotamine showed no appreciable hemolytic activity to erythrocytes. Our studies revealed that crotamine is also an AMP that kills bacteria through membrane permeabilization. However, crotamine appears to have a narrow antibacterial spectrum, distinct from many classical beta-defensins, reinforcing the notion that crotamine originated from the beta-defensin gene lineage, but has undergone significant functional diversification. The Journal of Antibiotics (2011) 64, 327-331; doi: 10.1038/ja.2011.10; published online 9 March 2011