Treatment of clinical isolates of human pathogenic bacteria, which were known to be resistant to multiple
commonly-used antibiotics, with refined leukocyte extracts from the American alligator (Alligator mississippiensis)
resulted in a time- and concentration-dependent inhibition of bacterial proliferation. The alligator leukocyte extract
exhibited the strongest antibacterial effect on Pseudomonas aeruginosa followed by Enterococcus faecium and then
Klebsiella pneumonia. The antibacterial activities were acid-soluble, heat-stable at 70°C for one h, sensitive to protease
treatment, and did not require divalent metal ions for antibacterial activity. Collectively, these data strongly suggest that
the molecule(s) responsible for the observed antibacterial activities are small, cationic antimicrobial peptides.