In Vitro Potential of Equine DEFA1 and eCATH1 as Alternative Antimicrobial Drugs in Rhodococcosis Treatment

Abstract

f Rhodococcus equi, the causal agent of rhodococcosis, is a severe pathogen of foals but also of immunodeficient humans, causing bronchopneumonia. The pathogen is often found together with Klebsiella pneumoniae or Streptococcus zooepidemicus in foals. Of great concern is the fact that some R. equi strains are already resistant to commonly used antibiotics. In the present study, we evaluated the in vitro potential of two equine antimicrobial peptides (AMPs), eCATH1 and DEFA1, as new drugs against R. equi and its associated pathogens. The peptides led to growth inhibition and death of R. equi and S. zooepidemicus at low micromolar concentrations. Moreover, eCATH1 was able to inhibit growth of K. pneumoniae. Both peptides caused rapid disruption of the R. equi membrane, leading to cell lysis. Interestingly, eCATH1 had a synergic effect together with rifampin. Furthermore, eCATH1 was not cytotoxic against mammalian cells at bacteriolytic concentrations and maintained its high killing activity even at physiological salt concentrations. Our data suggest that equine AMPs, especially eCATH1, may be promising candidates for alternative drugs to control R. equi in mono-and coinfections.

The Equine Antimicrobial Peptide eCATH1 Is Effective against the Facultative Intracellular Pathogen Rhodococcus equi in Mice

“…as well (19). Our observations are consistent with the work of Cirioni et al, who similarly reported a synergistic effect between rifampin and ␣-helical AMPs (magainin II and cecropin A) in Pseudomonas aeruginosa infection models in rats (25).…”

“…Our observations are consistent with the work of Cirioni et al, who similarly reported a synergistic effect between rifampin and ␣-helical AMPs (magainin II and cecropin A) in Pseudomonas aeruginosa infection models in rats (25). It was hypothesized that AMPs allow rifampin, an RNA polymerase inhibitor, to access its intracellular target by permeabilization of the bacterial membrane (19,36).…”

“…For this, mouse macrophages were naturally infected in vivo and further collected for in vitro treatment with eCATH1 and rifampin before CFU enumeration. As the two antimicrobials exhibited a synergistic interaction in vitro against extracellular R. equi (19), the combination eCATH1 and rifampin in the present ex vivo model was also assessed. Before the ex vivo experiment, cytotoxicity of eCATH1 and rifampin on mouse peritoneal macrophages revealed that, similarly to the J774.2 cell line, eCATH1 did not exhibit significant toxicity at 20 g/ml, whereas rifampin was found to exert significant toxicity at 20 g/ml (data not shown) (ANOVA test; P Ͻ 0.05).…”

“…The results of the in vivo toxicity and activity studies presented here agree with our previous investigations of eCATH1. Indeed, we recently reported that the in vitro activity of eCATH1 was not hampered by a physiological salt concentration and that the peptide was not toxic for various mammalian cell types in vitro (19).…”

Killing of Trypanozoon Parasites by the Equine Cathelicidin eCATH1

“…The synthetic eCATH1, which is an ␣-helical equine antimicrobial peptide composed of 26 amino acid residues, has been shown to have the most potent antimicrobial activity against bacteria (16). Previous work in our laboratory revealed that eCATH1 was not cytotoxic against mammalian cells at bacteriolytic concentrations (18), that it maintained its potent activity even at physiological salt concentrations (18), and that it effectively killed intracellular bacterial cells in an in vivo model of Rhodococcus equi-infected mice (19), supporting the idea that eCATH1 is a strong candidate for possible use as a therapeutic in animals.…”