Co-resistance: an opportunity for the bacteria and resistance genes

Co-resistance involves transfer of several genes into the same bacteria and/or the acquisition of mutations in different genetic loci affecting different antimicrobials whereas pleiotropic resistance implies the same genetic event affecting several antimicrobials. There is an increasing prevalence of isolates with co-resistance which are over-represented within the so-called high-risk clones. Compensatory events avoid fitness cost of co-resistance, even in the absence of antimicrobials. Nevertheless, they might be selected by different antimicrobials and a single agent might select co-resistant isolates. This process, named as co-selection, is not avoided with cycling or mixing strategies of antimicrobial use. Co-resistance and co-selection processes increase the opportunity for persistence of the bacteria and resistance genes and should be considered when designing strategies for decreasing antimicrobial resistance.

► Multidrug-resistant bacteria has increased over the past years.
► Co-resistance involves acquisition of mutations in different genetic loci and/or transfer of several resistance genes into the same bacteria.
► Isolates with co-resistance can be selected with different antimicrobials exerting co-selection processes.
► Cycling and mixing practices of antimicrobial use might facilitate co-resistance and co-selection processes.
► Co-resistance and co-selection processes increase the opportunity for persistence of the bacteria and the resistance genes.