Antibacterial Activity of Microbicidal Cationic Proteins 1 and 2, Natural Peptide Antibiotics of Rabbit Lung Macrophages

Microbicidal cationic proteins 1 and 2, peptides derived from rabbit lung macrophages, were tested for bactericidal activity against various bacterial species. Both were highly active against diverse gram-positive and gram-negative organisms under conditions of near-neutral pH (between 7 and 8) and relatively low ionic strength. Susceptible species included Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pneumoniae, Listeria monocytogenes, Pseudomonas aeruginosa, Klebsiella pneumoniae, Haemophilus influenzae, Escherichia coli, and Serratia marcescens. Streptococcus agalactiae, type 1A, was less susceptible than the aforementioned organisms or S. agalactiae, type 3. Bordetella bronchiseptica, a common commensal and pathogen of the rabbit respiratory tract, was completely resistant to both peptides.