Abstract

Staphylococcus pseudintermedius (SP), including multidrug-resistant SP (MDR-SP), and Malassezia pachydermatis (MP) are major canine cutaneous pathogens. Chlorhexidine-based shampoos, alone or containing azoles, are commonly used in veterinary dermatology; however, comparative data on commercially available products are limited. This study evaluated the in vitro antimicrobial activity of seven chlorhexidine-based shampoos against 30 clinical MDR-SP isolates and 30 clinical MP isolates. Six two-fold dilutions (1:16,000–1:512,000) of KetoChlor®, BioHex®, MAX Chlorhexidine 4%, Douxo S3™ Pyo, TrizCHLOR®4, Malaseb®, and MiconaHex+Triz® were tested using a broth microdilution assay. Minimum inhibitory, bactericidal, and fungicidal concentrations (MIC, MBC, and MFC) were determined. Malaseb® and MiconaHex+Triz® exhibited the lowest MIC and MBC/MFC values, although the observed differences represented a single two-fold dilution step, with MIC values of 1:128,000 against both MDR-SP and MP, and MBC/MFC values of 1:32,000 and 1:128,000, respectively. The remaining shampoos demonstrated bactericidal activity (MIC = 1:32,000/1:64,000; MBC = 1:16,000), while some exhibited MIC and MFC values of 1:64,000 against MP. MIC and MFC endpoints were not reached for a limited number of MP isolates. Overall, all shampoo formulations demonstrated substantial antimicrobial activity across the tested dilution range. Further clinical studies are needed to determine whether these in vitro differences translate into meaningful in vivo efficacy.

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