Is the Use of Monensin Another Trojan Horse for the Spread of Antimicrobial Resistance?

Antimicrobial resistance (AMR) is a complex and somewhat unpredictable phenomenon. Historically, the utilization of avoparcin in intensive farming during the latter part of the previous century led to the development of resistance to vancomycin, a crucial antibiotic in human medicine with life-saving properties. Currently, in the European Union, there is a growing reliance on the ionophore antibiotic monensin (MON), which acts both as a coccidiostat in poultry farming and as a preventative measure against ketosis in lactating cows. Although many researchers claim that MON does not induce cross-resistance to antibiotics of clinical relevance in human medicine, some conflicting reports exist. The numerous applications of MON in livestock farming and the consequent dissemination of the compound and its metabolites in the environment require further investigation to definitively ascertain whether MON represents a potential vector for the propagation of AMR. It is imperative to emphasize that antibiotics cannot substitute sound animal husbandry practices or tailored dietary regimens in line with the different production cycles of livestock. Consequently, a rigorous evaluation is indispensable to assess whether the economic benefits associated with MON usage justify its employment, also considering its local and global environmental ramifications and the potential risk of instigating AMR with increased costs for its control.