Global spread of ionophore resistance genes highlights AMR risk
A recent study published in mSphere reveals that the narA and narB genes, responsible for resistance to the polyether ionophores narasin, salinomycin, and maduramicin, are globally distributed and found in a broad range of bacterial species from various hosts, including humans. These genes, which form the narAB operon, were identified in over 2,400 isolates from 51 countries across multiple continents, underscoring their widespread presence.
Originally used in animal production to control coccidiosis and promote growth, ionophores are not employed in human medicine. However, the study highlights a concerning pattern: narAB genes frequently co-occur with other antimicrobial resistance (AMR) determinants, including those conferring resistance to clinically important antibiotics such as vancomycin, erythromycin, and tetracycline. This genetic linkage suggests a mechanism of co-selection, where ionophore use may inadvertently select for broader AMR profiles.
The detection of narAB in bacterial isolates from poultry, cattle, swine, and humans demonstrates a wide host range and raises the possibility of horizontal gene transfer between animal and human-associated bacteria. These findings challenge the long-standing assumption that ionophore use in agriculture is risk-free from a public health perspective.
In conclusion, while ionophores are not directly used in human therapy, their role in selecting for resistance genes linked to human-relevant antibiotics cannot be ignored. The global dissemination of narAB and its association with other AMR genes highlight the potential indirect contribution of ionophore use to the growing threat of antimicrobial resistance in human medicine.
