Purified Coxiella burnetii (Nine Mile, phase I) ricketssiae were expos
ed to a synthetic peptide (CAP37(20-44)) based on the amino acid seque
nce of CAP37 - a 37 K human neutrophil granule-associated cationic ant
imicrobial protein - and their capacity to infect L929 mouse fibroblas
t cells was assessed during a 10-day post-exposure period. Because the
parasite thrives within the acidic phagolysosome we anticipated that
CAP37(20-44) would have no adverse effect on the organism. This was bo
rne out by the experiments; however, to our surprise, treated C. burne
tii had a much greater capacity to infect L cells than the non-treated
counterpart. We speculate that the peptide exhibits opsonin-like prop
erties, enhancing attachment of the rickettsia to the host cell surfac
e and subsequent entry.