Is there an association between the use of antimicrobials in pigs and resistance levels in commensal E.coli after a period of major reduction in use?

Worldwide there is growing concern about the increase of antimicrobial resistance. Antimicrobial resistance (AMR) could be considered as the result of (over)usage of antimicrobials (AMs) in human beings and animals. In order to reduce further increase of AMR the government of the Netherlands together with the livestock sectors and vets developed an action plan to reduce the use of AMs, in the assumption that reduction is associated with reduction in resistance. The plan was focused on the reduction of AMs. Transparency in the use of AM's, creating awareness of the risks of AM use, improvement of the health status on pigfarms, and goals set by the government were part of this action plan. After a period of major reduction in the use of AMs, the question can be asked if there is an association between the use of AMs in pigs and resistance levels in commensal E.coli?

Materials and Methods: Data of the use of AMs were obtained from the Agricultural Economic Institute (2004 to 2012) and from data published by the Netherlands Veterinary Medicines Authority (SDa, 2011 -2014). Data of AMR were obtained from the Central Veterinary Institute as published in MARAN. Data of usage were given as defined daily dosage per animal per year (DDDAY), the data of the CVI were presented in percentages based on MIC’s interpreted using epidemiological cut-off values. Ten antibiotics were tested. Logistic regression analysis for grouped data (number of resistant isolates over the total tested) was used to obtain OR for E.coli isolated be resistant to each antimicrobial agent per 1 unit increase in total DDDA/Y or homologous use.

AM use increased from 2004 till 2009 and decreased thereafter with 53.6% (11 DDDA/Y) whereas the percentage of total AMR slowly increased till 2009 and decreased afterwards with 21.6%. Moreover restriction of the use of 3rd/4rd generation cephalosporins and fluorochinolons resulted in 86% and 100% reduction of cefatoxime and ciprafloxic resistance respectively. Total AMuse was positively related to resistance. One unit increase in DDDA/Y was associated to a ~8% increased odds of total and most AMs and up to 30-40% increased probability of ciprofolxacin ans nalidixic acid resistance.

The Dutch policy to set goals for the reduction in use, together with the measures taken by vets and farmers and the establishment of an independent authority (SDa) to analyze the data of the use of AMS at farm level, increased the awareness of vets and farmers of AMR and resulted in a major reduction in the use of AMs. The decrease in the use of AMs is associated with the decrease in AMR. Reduction in use has been proven an efficient way to reduce antimicrobial resistance in farm animals

Disclosure of Interest: None Declared.