In vitro activity of a commercial otological solution containing a novel antimicrobial peptide on 30 clinical isolates of Pseudomonas aeruginosa from canine otitis

In dogs, Pseudomonas aeruginosa (PA) infections fre- quently present as an acute suppurative otitis, with sev- ere inflammation, ulceration, discomfort and pain. This can be a therapeutic challenge that needs new effective treatment. The aim of this study was to evaluate the in vitro antimicrobial activity of a commercial otologi- cal solution (Peptivet oto solution: ICF, Cremona, Italy) containing 0.02% chlorhexidine digluconate (CLX), 0.4% Tris/0.1% EDTA and 0.5 ug/mL of the antimicrobial peptide AMP2041 on PA from canine oti- tis. Minimal bactericidal concentrations (MBCs) were evaluated by broth microdilution. Standardized bacte- rial suspensions were incubated with different concen- trations of the test solution at pH8 and 37 °C for 30 min and then spread plated for colony forming unit (CFU) counts. The dynamics of bacterial killing were evaluated with time-kill curves obtained with undiluted product and at MBC for each strain by aliquoting and plating 20 uL of the bacterial suspension for CFU counts at fixed intervals (30 sec, 1, 5, 10, 15 min, 24 and 48 h). The MBC was 1:32 for 1/30 strains and 1:64 for 29/30 strains. The geometric average was 1:62.54, equivalent to a concentration of 0.0003% CLX/ 0.0064% Tris/0.0016% EDTA/0.008 ug/mL AMP2041. The time-kill assays with the undiluted product showed complete bactericidal effect within 5 min for all isolates, while at MBC this effect was reached within 10 min for 28/30 isolates. Complete bactericidal activity was observed after 48 h for all strains. The product evalu- ated in this study shows fast, complete and long-lasting antimicrobial activity against a panel of 30 PA clinical isolates from dogs with otitis