In vitro antibacterial and antibiofilm effects of mupirocin spray against Staphylococcus pseudintermedius.

Mupirocin is an effective antibiotic for infectious skin diseases. However, mupirocin is formulated as an ointment and is difficult to apply in canine systemic pyoderma. Therefore, many clinicians reformulate mupirocin off-label ointment into a spray. This study aimed to evaluate the antibacterial and antibiofilm effects of different concentrations of mupirocin spray (2%, 1%, and 0.5%) on Staphylococcus pseudintermedius over 21 days. Mupirocin spray was prepared by mixing mupirocin ointment and distilled water. The antibacterial effects were evaluated by measuring the optical density using broth microdilution assay and by live/dead staining. The antibiofilm activity of mupirocin spray was measured using a crystal violet staining method. All concentrations of mupirocin spray inhibited the growth of S. pseudintermedius. Mupirocin spray also inhibited biofilm formation of each isolate, although the degree of inhibition was influenced by the mupirocin concentration. The antibacterial and antibiofilm effects of mupirocin spray were maintained for 21 days. The 2% and 1% mupirocin sprays exhibited significantly better antibacterial and antibiofilm efficacy than the 0.5% mupirocin spray. Thus, 1-2% mupirocin spray may be effective for clinical use. Mupirocin spray is convenient and effective for the treatment of canine systemic pyoderma caused by S. pseudintermedius infection.