Cathelicidins are antimicrobial peptides from sheep (SMAP29 and SMAP34), rabbits (CAP11 and CAP18), rodents (CRAMP), and humans (FALL39, LL37, and h/CAP18). In a broth microdilution assay against nine ovine pathogens, SMAP29, SMAP34, mouse CRAMP, CAP18, CAP18 31 , CAP18 28 , CAP18 22 , and CAP18 21a were the most active, with MICs as low as 0.6 g/ml. Other cathelicidins were less active. In lambs with pneumonia, 0.5 mg of SMAP29 reduced the concentration of bacteria in both bronchoalveolar lavage fluid and consolidated pulmonary tissues. Hence, the antimicrobial activity of SMAP29 suggests that it has applications in the treatment of respiratory tract infections.

SMAP29, an ovine cathelicidin, was systematically altered to create a family of 23 related peptides for MIC and minimum bactericidal concentration determinations. SMAP28, SMAP29, and a derivative of SMAP29 called ovispirin were all antimicrobial. However, many congeners of SMAP29 and ovispirin were not as active as the parent molecules. With immunoelectron microscopy, SMAP29 was seen on membranes and within the cytoplasm of Pseudomonas aeruginosa PAO1.

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