The aim of the current study was to elucidate the contribution of AMPs in innate immunity against different Nocardia species. We therefore investigated the activity of several
important epithelial- and neutrophil-derived human and bovine AMPs against the four nocardial species N. farcinica, N. nova, N. asteroides and N. brasiliensis, all of whichrepresent major human and bovine pathogens. Results and Discussion Levofloxacin was used as killing control to compare antinocardial potency of Selleck CYC202 tested AMPs and showed dose-dependent activity against all four nocardial strains. The peptide DPY without antimicrobial activity served as negative control and exhibited Selleck Alvocidib no activity against all tested selleckchem Nocardia strains (data not shown). Activity of human AMPs against Nocardia species All tested human AMPs exhibited activity against N. farcinica ATCC 3318 (Figure 1A) and N. nova ATCC 33726 (Figure 1B). Human β-defensin hBD-3 revealed strongest activity with LD90 of 16 μg/ml against both strains. Human cathelicidin LL-37 showed LD90 of 32 μg/ml respectively. Accordingly, we found human α-defensins HNP 1-3 to be active, although higher concentrations were needed with LD90 >32 μg/ml against N. farcinica and LD90 of 64 μg/ml against N. nova (Table 1). Notably, hBD-3 and LL-37 were found to be more potent against N. nova than levofloxacin in equivalent concentrations.
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), Interleukin-2 receptor 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. Table 1 Susceptibility of different Nocardia species against innate defense AMPs LD90(μg/ml) (killing/CFU reduction in percent ± SD) Species
levoflox HNP 1-3 LL-37 hBD-3 indolicidin LAP TAP N. farcinica ATCC 3318 8 (92.3 ± 3.8) >32 32 (96.6 ± 0.6) 16 (92.5 ± 5.3) 16 (96.7 ± 1.7) 16 (92.9 ± 7.1) 32 (94 ± 5.1) N. nova ATCC 33726 >32 64 (97.2 ± 3.6) 32 (91.4 ± 7.0) 16 (95.2 ± 1.7) 8 (90.5 ± 3.4) n.d. n.d. N. asteroides ATCC 19247 8 (92.6 ± 3.8) 32 (90.9 ± 0.6) >64 >64 64 (99.1 ± 0.6) n.d. n.d. N. brasiliensis ATCC 19296 32 (96.6 ± 2.2) >64 >64 >64 64 (92.9 ± 2.1) >64 >64 LD90 denotes the lowest peptide concentration leading to a = 90% reduction of CFU after incubation (12 h or 16 h) with AMPs or levofloxacin. Presented data are LD90 determinations based on means of at least four (levofloxacin, HNP 1-3, LL-37 and hBD-3) or two (indolicidin, LAP and TAP) independent sets of experiments with each Nocardia species.