Antimicrobial properties of two purified skin peptides from the mink frog (Rana septentrionalis) against bacteria isolated from the natural habitat

Numerous peptides exhibiting antimicrobial properties have been isolated from the skins of many amphibian species. These peptides offer an innate chemical defense system against various microbial agents that exist in the amphibian's environment. Amphibian skin peptides are typically tested for antimicrobial activity against microbial strains that are pathogenic to humans, but not on potential pathogenic or opportunistic bacteria that exist in the organism's habitat. Two peptides, a brevinin-2-related peptide and temporin-1SPb previously isolated from secretions of the mink frog, Rana septentrionalis, were tested for antimicrobial activity on bacterial isolates endemic to the frog's habitat. Ten isolates were identified, using 16S rRNA gene sequencing techniques, in the genera Pseudomonas, Serratia, Bacillus, Aeromonas, Burkholderia, Microbacterium, and Delftia. Bacterial isolates were tested with peptides at concentrations ranging from 0.8 microM to 1000 microM to determine the minimum inhibitory concentration (MIC) to inhibit growth. Growth of four of the isolates was inhibited by temporin-1SPb at the concentrations used, but all of the isolates were inhibited by the brevinin-2-related within the range of peptide concentrations used. This demonstrates the efficacy of both peptides as a component of the frog's innate chemical defense system.