Differential activity of innate defense antimicrobial peptides against Nocardia species

Abstract

Background: Members of the genus Nocardia are ubiquitous environmental saprophytes capable to cause human pulmonary, disseminated and cutaneous nocardiosis or bovine mastitis. Innate immunity appears to play an important role in early defense against Nocardia species. To elucidate the contribution of antimicrobial peptides (AMPs) in innate defense against Nocardia, the activity of human alpha-defensins human neutrophil peptides (HNPs) 1-3, human beta-defensin (hBD)-3 and cathelicidin LL-37 as well as bovine beta-defensins lingual and tracheal antimicrobial peptides (LAP, TAP) and bovine neutrophil-derived indolicidin against four important Nocardia species was investigated.

Results: Whereas N. farcinica ATCC 3318 and N. nova ATCC 33726 were found to be susceptible to all investigated human and bovine AMPs, N. asteroides ATCC 19247 was killed exclusively by neutrophil-derived human alpha-defensins HNP 1-3 and bovine indolicidin. N. brasiliensis ATCC 19296 was found to exhibit complete resistance to investigated human AMPs and to be susceptible only to bovine indolicidin.

Conclusion: Selected AMPs are capable to contribute to the first line of defense against Nocardia, yet, susceptibility appears to vary across different Nocardia species. Obtained results of neutrophil-derived AMPs to possess the broadest antinocardial spectrum are remarkable, since nocardiosis is characterized by a neutrophil-rich infiltrate in vivo.

Figure 1

Activity of human AMPs HNP 1-3, hBD-3, LL-37 and levofloxacin (killing control) against A N. farcinca ATCC 3318 (p < 0.05 for all tested substances), B N. nova ATCC 33726 (p < 0.05 for all tested substances), C N. asteroides ATCC 19247 (levofloxacin p < 0.05, HNP1-3 p = 0.11) and D N. brasiliensis ATCC 19296 (levofloxacin p < 0.05) was investigated using a colony forming unit (CFU) assay. Data are means (percent CFU reduction) of at least four independent sets of experiments with each peptide and each Nocardia species.

Figure 2

Additive activity of the two AMPs HNP 1-3 and LL-37 in a colony forming unit (CFU) assay against N. farcinica ATCC 3318. A combination of HNP 1-3 and LL-37 exhibited killing comparable to each peptide alone at twofold higher concentrations (i.e. 78.9% CFU reduction by 8 μg/ml HNP 1-3 in combination with 8 μg/ml LL-37 compared to 68.5% CFU reduction by 16 μg/ml LL-37 or 45.6% reduction by 16 μg/ml HNP 1-3 alone). Data are results of a single assay.

Figure 3

Activity of bovine AMPs TAP, LAP indolicidin and levofloxacin (killing control) against A N. farcinca ATCC 3318 (p < 0.05 for all tested substances), B N. brasiliensis ATCC 19296 (indolicidin and levofloxacin p < 0.05) was investigated using a colony forming unit (CFU) assay. Data are means (percent CFU reduction) of at least two independent sets of experiments with each peptide and each Nocardia species.