Abstract
The treatment of diarrhea in the postweaning period is a common reason for the use of antimicrobials in pig production, and Escherichia coli is the single most important causative agent for this condition. Colistin has recently been classified as a critically important antimicrobial for human health, as it is a last-resort drug against certain multi-drug-resistant Gram-negative bacteria. Therefore, the use of colistin has been significantly reduced in some countries, including Denmark. Despite this, the drug is still commonly used to treat diarrhea in pigs in many countries, and there is a need to understand the risks associated with this practice. We performed a prospective cohort study to investigate the effect of colistin treatment on the changes in the average minimum inhibitory concentration (MIC) in commensal E. coli in a pig herd where no colistin-resistant bacteria were detectable before treatment. One group of pigs was batch treated with colistin after the clinical observation of diarrhea, one group was batch treated with colistin approximately 10 days before the expected onset of diarrhea, and a control group was not treated with colistin but provided with nonantimicrobial antidiarrheal feed supplement. Treatment with colistin in the dose and time combinations used did not result in a significant increase in the average colistin MIC values in E. coli. Moreover, no E. coli strains showed a MIC above the breakpoint of >2 mg/L against colistin. Co-selection of resistance to other antimicrobials was not observed.
Highlights
Antimicrobial resistance (AMR) is considered a threat to human health
In G1, the animals received the colistin treatment when the farmer evaluated that number of diarrheal droppings exceeded a pre-fixed level
As colistin resistance in E. coli is rare in Danish pigs, it was interesting to see whether the presumptive colistin-resistant E. coli isolated (n = 105) from these two groups were truly resistant
Summary
Antimicrobial resistance (AMR) is considered a threat to human health. At least 700,000 people die annually from infection caused by AMR bacteria, and if appropriate actions are not taken, it has been estimated that by the year 2050, this number may reach up to 10 million, and the cost will be up to USD 100 trillion annually [1]. AMR causes an increased cost of treatment and threatens the wellbeing of animals. Colistin has been used extensively for the treatment of diarrhea caused by E. coli in weaner pigs, and for several decades, it has been a frequent choice of drug for this indication in pigs [7,8]. Colistin is still commonly used for the treatment of diarrhea in pigs, and it is important to know how this affects resistance development
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