Redefining cross-resistance, co-resistance and co-selection: beyond confusion?

The similarity of current definitions of 'cross-resistance' and 'co-resistance' continues to cause confusion both in the scientific community as well as in understanding policies and in particular when looking at resistance from a risk assessment perspective. Further, lack of harmonized definitions of these terms in the regulatory space is challenging for interpretation. The purpose of this article is to: (i) provide an overview of the ambiguity in existing terminology related to cross-resistance, co-resistance and co-selection; (ii) emphasize the challenges created by the use of poor terminology in research and scientific literature; and (iii) propose a clear set of harmonized definitions that could be put into use through international regulatory agencies and institutions, such as the World Health Organization, Food and Drug Administration, European Medicines Agency, Center for Disease Control, Committee for Veterinary Medicinal Products, World Organization for Animal Health/Office International des Epizooties and the Food and Agriculture Organization of the United Nations.