Assessment of chlorhexidine activity against Staphylococcus pseudintermedius from skin and soft-tissue infections in companion animals.

C Morais, Carolina Ferreira, Paula Zacharias, P. Abrantes, Constança Pomba, SS Costa, I Couto

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Abstract

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.
Original languageEnglish
Publication statusPublished - 18 Apr 2023
Event33rd European Congress of Clinical Microbiology and Infectious Diseases - Copenhagen, Denmark
Duration: 15 Apr 202318 Apr 2023

Conference

Conference33rd European Congress of Clinical Microbiology and Infectious Diseases
Abbreviated title33rd ECCMID
Country/TerritoryDenmark
CityCopenhagen
Period15/04/2318/04/23

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