Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 10, 2007
Publication Date: November 1, 2007
Citation: Chockalingam, A., Mckinney, C.E., Rinaldi, M., Zarlenga, D.S., Bannerman, D.D. 2007. A peptide derived from human bactericidal/permeability-increasing protein (BPI) exerts bactericidal activity against Gram-negative bacterial isolates obtained from clinical cases of bovine mastitis. Veterinary Microbiology. 125(1-2):80-90.
Interpretive Summary: The therapeutic efficacy of the most common antibiotics used to treat intramammary Gram-negative bacterial infections (e.g., Escherichia coli) remains suboptimal. Further, therapeutics that can counteract the deleterious systemic inflammatory response that is evoked by bacterial endotoxin expressed by these bacteria remain lacking. The current manuscript identifies a peptide with sequences derived from an endogenous human protein, bactericidal/permeability-increasing protein (BPI), which is directly bactericidal to various Gram-negative bacteria isolated from cases of clinical mastitis. In addition, the reported findings demonstrate an ability of this peptide to neutralize bacterial endotoxin. Together, this manuscript identifies a peptide with potential therapeutic application for the management of local and systemic Gram-negative infections in cattle.
Gram-negative bacteria are responsible for approximately one-third of the clinical cases of bovine mastitis and can elicit a life-threatening, systemic inflammatory response. Lipopolysaccharide (LPS) is a membrane component of all Gram-negative bacteria and is largely responsible for evoking the deleterious inflammatory response. Antibiotic and anti-inflammatory therapy for treating intramammary Gram-negative infections remains suboptimal. Bactericidal/permeability-increasing protein (BPI) is a neutrophil-derived protein that contains antimicrobial and LPS-neutralizing properties. Select peptide derivatives of the protein are reported to retain these properties. The objective of this study was to evaluate the antimicrobial activity of a human BPI-derived synthetic peptide against clinical bovine mastitis isolates of Gram-negative bacteria. A hybrid peptide was synthesized corresponding to two regions of human BPI (amino acids 90-99 and 148-161), the former of which has bactericidal activity and the latter of which has LPS-neutralizing activity. The minimum inhibitory (MIC) and bactericidal (MBC) concentrations of this peptide against various species of bacteria were determined using a broth microdilution assay. The MIC's were determined to be: 16-64 'g/ml against Escherichia coli; 32-128 'g/ml against Klebsiella pneumoniae and Enterobacter spp; and 64-256 'g/ml against Pseudomonas aeruginosa. The MBC's were equivalent to or 1-fold greater than corresponding MIC values. The peptide had no growth inhibitory effect on Serratia marcescens. The antimicrobial activity of the peptide was retained in the presence of serum, but severely impaired in milk. Further functional evaluation of the peptide demonstrated its ability to completely neutralize LPS. Together, these data support additional investigations into the potential therapeutic application of BPI to the treatment of Gram-negative infections and associated inflammatory complications in cattle.