Efflux as a resistance mechanism in the veterinary pathogen Staphylococcus pseudintermedius

Marta Leal, C Morais, Bárbara Ramos, P. Abrantes, Constança Pomba, SS Costa, Constança Pomba

Research output: Contribution to conferencePosterpeer-review


Background: Staphylococcus pseudintermedius is the main bacterial cause of skin and soft tissue (SSTI) infections in companion animals, particularly dogs. The emergence of methicillin-resistant strains (MRSP), many times associated with a multidrug resistance phenotype is a public health concern.

Objective: To evaluate efflux, a resistance mechanism still poorly characterized in S. pseudintermedius, as a contributor to biocide and fluoroquinolone resistance.

Methods: Susceptibility to the efflux pump substrates ethidium bromide (EtBr), tetraphenylphosphonium bromide (TPP) and ciprofloxacin (CIP) was evaluated by MIC determination for 155 SSTI-related S. pseudintermedius isolated from companion animals. EtBr and TPP MIC distributions were analyzed and used to estimate cut-off (COWT) values. The effect of the efflux inhibitors (EIs) thioridazine and verapamil on MICs was assessed. Real-time fluorometric EtBr accumulation assays were performed with/without glucose and/or EIs.

Results: Applying the estimated COWT value for TPP revealed the presence of a non-wild type population towards TPP with increased efflux. Characterization of this efflux activity showed that it is strain-specific and glucose-dependent. Resistance to fluoroquinolones was mainly linked to target gene mutations, yet a contribution of efflux to ciprofloxacin resistance levels could not be ruled out.

Conclusion: This study describes the relevance of efflux-mediated resistance in S. pseudintermedius, particularly to biocides, and provides the methodological basis for further studies on efflux activity in this important veterinary pathogen.

Funding: Project BIOSAFE funded by FEDER/FCT (Portugal), Grant LISBOA-01-0145- FEDER-030713, PTDC/CAL-EST/30713/2017. Further support by FCT to GHTM (UID/04413/2020) and (CM) UI/BD/151061/2021.
Original languageEnglish
Publication statusPublished - 21 Apr 2023
Event6º Congresso Nacional de Medicina Tropical - IHMT, Lisboa, Portugal
Duration: 20 Apr 202321 Apr 2023


Conference6º Congresso Nacional de Medicina Tropical
Abbreviated title6º CNMT
Internet address


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