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Assessment of chlorhexidine activity against Staphylococcus pseudintermedius from skin and soft-tissue infections in companion animals.
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Background Staphylococcus aureus and Staphylococcus pseudintermedius are responsible for skin and soft-tissue infections (SSTIs) in companion animals and are increasingly associated with antimicrobial resistance (AMR). Chlorhexidine (CHX) is one of the most used and recommended antisseptic in the treatment of SSTIs in these animals. This study analyzed the effectiveness, at different conditions, of CHX against S. aureus and S. pseudintermedius causing SSTIs in companion animals. Methods CHX time-kill assays were performed according to the European Standard EN 1040[1] for reference strains S. aureus ATCC25923 and S. pseudintermedius DSM21284T and four clinical isolates with AMR traits (methicillin-resistant and multidrug-resistant) and clonal lineages [ST22/ST105 (S. aureus), ST71/ST118 (S. pseudintermedius)] representative of a wide collection. Assays were conducted at 38.5˚C (dog skin temperature), using increasing CHX levels, from sub-inhibitory (1/2 MIC) to the in-use concentration. The CHX killing effect was evaluated at several time points, from 1 min up to 24h, that included the general recommended exposure time for antiseptics (5/10 min). Results CHX showed effectiveness absence of bacterial growth for all strains at the recommended inuse concentration and times of exposure (5/10 min). However, at these time points, suboptimal concentrations resulted in lower efficacy (reduction up to ≈4 log CFU/mL). This lower efficacy was more evident in clinical strains, which could withstand concentrations up to 50xMIC. Moreover, at 24h of exposure growth was still observable for both S. aureus clinical strains at concentrations up to 10xMIC and for S. pseudintermedius clinical strains at ½ MIC and MIC. Overall, S. pseudintermedius is more susceptible to CHX action than S. aureus. Conclusions This undergoing study suggests that the CHX effect is immediate when used at the recommended use conditions (concentration and exposure time). However, at lower concentrations, biocide efficacy may be compromised, particularly against S. aureus. This indicates that the inappropriate use of biocides, such as incomplete removal of the product from the animal skin, could potentially select strains with lower susceptibility to biocides and antibiotics that share the same resistance mechanisms and thus promote AMR dissemination in these relevant veterinary pathogens. Project BIOSAFE funded by FEDER through - COMPETE and Fundação para a Ciência e a Tecnologia (FCT, Portugal), Grant LISBOA-01-0145-FEDER-030713, PTDC/CALEST/ 30713/2017. Further support by FCT to GHTM (UID/04413/2020). Grants UI/BD/151061/2021 and 2021.05063.BD awarded by FCT to CM and CF, respectively.
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General Pharmacology, Toxicology and Pharmaceutics Drug Discovery General Veterinary Infectious Diseases Microbiology (medical) SDG 3 - Good Health and Well-being SDG 9 - Industry, Innovation, and Infrastructure