Inhibition of frog antimicrobial peptides by extracellular products of the bacterial pathogen Aeromonas hydrophila

Aims:  To determine whether the extracellular products (ECPs) from Aeromonas hydrophila , a frog bacterial pathogen that is resistant to skin antimicrobial peptides of three different frog species Xenopus laevis , Litoria aurea and Litoria raniformis , can modulate the activity of these peptides.
Methods and Results:  ECPs were collected from cultures of Klebsiella pneumoniae , a pathogen susceptible to skin antimicrobial peptides of all three tested frog species, and from cultures of Aer .  hydrophila . They were tested for protease activity and for inhibition of the antimicrobial activity of natural peptide mixtures and single peptides of all three frog species against Escherichia coli ATCC 25922. ECPs from cultures of Aer .  hydrophila grown for 16, 24 and 36 h showed protease activity and inhibited the antibacterial activity of all peptides against E .  coli ATCC 25922. In contrast, the ECPs from cultures of Kl .  pneumoniae neither had protease activity nor inhibited the activity of any peptides.
Conclusion:  The proteolytic ECPs of Aer .  hydrophila have the ability to inhibit the skin antimicrobial peptides of frogs.
Significance and Impact of the Study:  The results of this study provide new information on the association of ECPs with the resistance of Aer .  hydrophila to frog antimicrobial peptides.