Antibacterial Effect of the In Vitro Interaction Between Clotrimazole and Chlorhexidine Against Staphylococcus pseudintermedius With Known Resistance Patterns Isolated From Canine Pyoderma.

BACKGROUND

Staphylococcus pseudintermedius is the main etiological agent of canine pyoderma and exhibits increasing multidrug resistance. Due to the reduced efficacy of antimicrobials, topical combinations of antimicrobial agents-such as chlorhexidine (CHX) and clotrimazole (CLT)-have gained attention as an alternative.

OBJECTIVE

To evaluate the in vitro antibacterial activity and pharmacological interaction of a 2:1 CHX-CLT combination against S. pseudintermedius isolates from canine pyoderma.

MATERIALS AND

METHODS

Sixteen isolates of S. pseudintermedius were obtained from canine pyoderma and identified by PCR detection of the nuc gene. Methicillin resistance was assessed both phenotypically, by oxacillin disk diffusion, and genotypically, through mecA detection. Minimum inhibitory concentrations for CHX, CLT and their 2:1 combination were determined by broth microdilution using resazurin. The fractional inhibitory concentration index was calculated to assess drug interaction.

RESULTS

All isolates carried both nuc and mecA genes, while only 25% were phenotypically resistant to oxacillin. CHX exhibited MIC50 and MIC90 values of 0.781 and 1.562 µg/mL, respectively; CLT showed 6.25 and 12.5 µg/mL. In the 2:1 CHX-CLT combination, MICs were reduced up to 6-fold, with MIC50 and MIC90 values of 0.39-0.781 µg/mL (CHX) and 0.195-0.39 µg/mL (CLT). The interaction was additive in 81.25% of isolates and indifferent in the remainder.

CONCLUSIONS

The CHX-CLT combination demonstrated enhanced in vitro antibacterial activity with predominantly additive interactions against S. pseudintermedius. The results support the rational use of CHX-CLT topical formulations as an effective therapeutic alternative for canine pyoderma in the context of growing antimicrobial resistance.