Decrease in colistin resistance among young bovine and pig productions in France: relationship with colistin usage...

Colistin is a last-line antibiotic used to treat multiresistant human infections. The emergence of resistance in animal productions led to recommendations to reduce the veterinary use of colistin over the last decade. A long-term evaluation of policies on colistin usage is now deemed necessary.

This study aims to identify the stewardship measures regarding colistin usage in pig and bovine productions in France and characterize their long-term effects on colistin use and resistance.

Measures contributing to colistin stewardship were inventoried from regulators, stakeholders and professionals. Data were collected from antimicrobial usage monitoring systems (i.e. national sales and on-farm usage) and two resistance surveillance programmes (one dedicated to clinical isolates and the other to commensal ones). Two time series-one of animal exposure to colistin and the other showing corresponding Escherichia coli resistance-and their relationships were analysed for the 2008-23 period.

Numerous different stewardship measures were progressively implemented in France during the study period. Colistin exposure significantly decreased in both bovine and pig productions, reaching a plateau in recent years. Colistin resistance concomitantly and markedly decreased, both time series being significantly associated.

The long-term data available in France on colistin use and colistin resistance enabled analysis of the long-term impact of stewardship measures on the exposure of pigs and cattle, together with bacterial resistance to colistin. Both have significantly decreased towards a plateau, reflecting the effectiveness of the measures adopted to preserve colistin's usefulness in animal and human health.