Multidrug Efflux System-mediated resistance in Staphylococcus aureus under a One Health approach

The aim of the study was to track the spread of antimicrobial resistance among the different sectors of One Health through the detection of Multidrug-Efflux-System in multidrug-resistant Staphylococcus aureus isolates. Multidrug-resistant (MDR) and methicillin-resistant (MRSA) S. aureus isolates were selected: 25 of human, one of animal and eight of food origin. The efflux system genes norA, norB, norC, LmrS, tet38 and msrA were screened by PCR. The activity of the efflux systems was determined by the minimum inhibitory concentration (MIC) of tetracycline and ciprofloxacin in the presence and absence of CCCP and in the quantification of ethidium bromide efflux. Furthermore, biofilm formation was determined in the presence and absence of the CCCP. The molecular epidemiology of the isolates was traced with the aid of PFGE. The gene norC was the most prevalent, detected in all isolates and msrA was the least prevalent, detected in only two isolates from humans. There was no difference in the MICs of tetracycline and ciprofloxacin in the presence of CCCP, but 55.9% of isolates showed ethidium bromide efflux. The presence of CCCP decreased the biofilm formation. Regarding the molecular epidemiology, in three clusters was a mixture of the isolates from different origins. Therefore, S. aureus MDR with active multidrug efflux systems are circulating between One Health domains and it is necessary to consider strategies to decrease this circulation in order to prevent the dissemination of resistance mediated by MES.