Antimicrobial activity of bovine bactericidal permeability-increasing protein-derived peptides against gram-negative bacteria isolated from the milk of cows with clinical mastitis

Objective-To evaluate antimicrobial activity of bovine bactericidal permeability-increasing protein (bBPI)-derived synthetic peptices against mastitis-causing gram-negative bacteria. Sample Population-Bacterial isolates from the milk of cows with clinical mastitis. Procedures-3 pepticles were synthesized with sequences corresponding to amino acids 65 to 99 (bBPI(65-99)) or 142 to 169 (bBPI(142-1 39)) or the combination of amino acids 90 to 99 and 148 to 161 (bBPI(90-99,148-161)) of bBPl. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBQ of these pepticles against bacterial isolates from cows with mastitis were determined by use of a standardized broth microdilution assay. The ability of these pepticles to retain their antimicrobial activity in serum and milk was also evaluated. Finally, bacterial lipopolysaccharide (LPS)-neutralizing activity of these pepticles was assayed with the Limulus amebocyte lysate test. Results-Of the 3 pepticles tested, bBPI(9,-,9,14,-161) had the widest spectrum of antimicrobial activity, with MIC and MBC values ranging from 16 to 64 mu g/mL against Escherichia coli, Klebsiella pneumoniae, and Enterobacter spp and from 64 to 128 mu g/mL against Pseudomonas aeruginosa. None of the peptices had any growth-inhibitory effect on Serratia marcescens. The antimicrobial activity of bBPI,,-,,14,- I was inhibited in milk, but preserved in serum. Finally, bBPI(142-16), and bBPI(90-99,148-161) completely neutralized LPS. Conclusions and Clinical Relevance-bBPI(90-99,148-161) is a potent neutralizer of the highly proinflammatory molecule bacterial LPS and has antimicrobial activity against a variety of gram-negative bacteria. The ability of bBPI(90-99,148-161) to retain antimicrobial activity in serum suggests a potential therapeutic application for this peptide in the management of gram-negative septicemia.