In vitro effectiveness of the antimicrobial peptide eCATH1 against antibiotic-resistant bacterial pathogens of horses.

The equine antimicrobial peptide eCATH1 previously has been shown to have in vitro activity against antibiotic-susceptible reference strains of Rhodococcus equi and common respiratory bacterial pathogens of foals. Interestingly, eCATH1 was also found to be effective in the treatment of R. equi infection induced in mice. The aim of this study was to assess the in vitro activity of eCATH1 against equine isolates of Gram-negative (Escherichia coli, Salmonella enterica, Klebsiella pneumoniae and Pseudomonas spp.) and Gram-positive (R. equi, Staphylococcus aureus) bacteria resistant to multiple classes of conventional antibiotics. A modified microdilution method was used to evaluate the minimum inhibitory concentrations (MICs) of the antimicrobial peptide. The study revealed that eCATH1 was active against all equine isolates of E. coli, S. enterica, K. pneumoniae, Pseudomonas spp. and R. equi tested, with MICs of 0.5-16 μg mL(-1), but was not active against most isolates of S. aureus. In conclusion, the activity of the equine antimicrobial peptide eCATH1 appears to not be hampered by the antibiotic resistance of clinical isolates. Thus, the data suggest that eCATH1 could be useful, not only in the treatment of R. equi infections, but also of infections caused by multidrug-resistant Gram-negative pathogens.