Sensitivity of Chlamydia suis to cathelicidin peptides

Nine Chlamydia suis isolates, obtained from pigs with conjunctivitis, were molecularly characterized by ompA sequencing and their in vitro susceptibility to six cathelicidin peptides (SMAP-29, BAC-7, BMAP-27, BMAP-27, BMAP-28, PG-1, LL-37) determined in cell culture. SMAP-29 was the most active peptide, reducing the intracellular inclusion number by ≥50% at a concentration of 10 μg/ml (3 μM) in six of the nine isolates tested. Three molecularly identical isolates were insensitive at a concentration as high as 80 μg/ml (25 μM). Of the remaining cathelicidin peptides tested, BAC-7 and BMAP-27 were active against six C. suis isolates at a concentration of 80 μg/ml (25 and 26 μM, respectively). Cathelicidins LL-37 and PG-1 did not show any anti-chlamydial activity at 80 μg/ml.