BACKGROUND: Antimicrobial peptides (AMPs) are small proteins present in most living species and they are involved in the defence against pathogenic organisms. β-Defensins and cathelicidin are the most frequently studied AMPs in both people and dogs.
HYPOTHESIS/OBJECTIVES: Our objectives were to determine the minimal inhibitory concentration and minimal bactericidal concentration of two canine β-defensins and a cathelicidin against antibiotic-sensitive and antibiotic-resistant bacteria and yeasts using a broth microdilution method.
METHODS: The micro-organisms tested were ATCC strains of meticillin-sensitive and meticillin-resistant Staphylococcus aureus (MSSA and MRSA, respectively), meticillin-sensitive Staphylococcus pseudintermedius (MSSP), Escherichia coli, Pseudomonas aeruginosa, Candida albicans and Malassezia pachydermatis. Field strains of meticillin-resistant S, pseudintermedius (MRSP, n = 1) and MSSP (n = 11) were also tested. Mann-Whitney U-test and Friedman test were used for statistical analysis.
RESULTS: The MSSP and MRSP were more susceptible to canine AMPs than MSSA and MRSA. Malassezia pachydermatis was more sensitive than C. albicans to canine AMPs. The β-defensin cBD103 was most effective against Staphylococci and P. aeruginosa, while the cathelicidin cCath was the most effective AMP against E. coli. Additionally, cBD103 was the most effective AMP for both yeasts studied, with M. pachydermatis being more susceptible than C. albicans. All AMPs tested exhibited killing within 2 h of exposure.
CONCLUSIONS AND CLINICAL IMPORTANCE: We demonstrated that natural canine AMPs are effective against canine-specific pathogens, are equally effective against meticillin-resistant or -susceptible strains, and are more effective against M. pachydermatis than against C. albicans organisms.