In vitro comparison of the effectiveness of polihexanide and chlorhexidine against canine isolates of Staphylococcus pseudintermedius, Pseudomonas aeruginosa and Malassezia pachydermatis

Background - Polihexanide (polyhexamethylene biguanide) is an antiseptic substance that plays a prominent role in the treatment of critically colonized or infected acute and chronic wounds in humans. Hypothesis/Objectives - The aim of this study was to assess the in vitro antimicrobial efficacy of polihexanide against canine isolates of Staphylococcus pseudintermedius, Pseudomonas aeruginosa and Malassezia pachydermatis and compare it with 4.5% chlorhexidine digluconate for two different contact times. Methods - Ten isolates of each organism were incubated at 37 degrees C for 3 and 5 min, respectively, with each antiseptic diluted 1:2 to 1:4096 in phosphate-buffered saline. Results - Both products showed excellent antimicrobial activity against all isolates tested. No significant differences in antimicrobial efficacy between antiseptics for all isolates were found. With the exception of one isolate of M. pachydermatis at 3 min exposure time, all isolates were completely killed by a dilution of 1:32 of polihexanide as well as chlorhexidine at both exposure times. Although the mean values of break-point concentrations for both antiseptics increased with the longer exposure time of 5 min, there were no significant differences between the two exposure times. The P. aeruginosa isolates were more susceptible than S. pseudintermedius for both antiseptics, and break-point dilutions were significantly higher compared with break-point dilutions obtained by all other treatments. Conclusions and clinical importance - The results indicate that polihexanide has comparable in vitro antimicrobial efficacy to chlorhexidine and presents a potential alternative agent for skin and wound antisepsis in veterinary medicine.