Antimicrobial resistance and its relationship with antimicrobial use on Austrian dairy farms

Thomas Werner; Annemarie Käsbohrer; Barbara Wasner; Sandra Köberl-Jelovcan; Sebastian G Vetter; Christa Egger-Danner; Klemens Fuchs; Walter Obritzhauser; Clair L Firth

doi:10.3389/fvets.2023.1225826

Antimicrobial resistance and its relationship with antimicrobial use on Austrian dairy farms

Front Vet Sci. 2023 Jul 21:10:1225826. doi: 10.3389/fvets.2023.1225826. eCollection 2023.

Authors

Affiliations

¹ Unit of Veterinary Public Health and Epidemiology, Institute of Food Safety, Food Technology and Veterinary Public Health, University of Veterinary Medicine, Vienna, Austria.
² Department for Biological Safety, German Federal Institute for Risk Assessment, Berlin, Germany.
³ Upper Austrian Animal Health Organization Laboratory, Clinical Microbiology, Upper Austrian Animal Health Organization, Ried im Innkreis, Austria.
⁴ Institute for Medical Microbiology and Hygiene, Centre for Foodborne Infectious Diseases, Division of Public Health, Austrian Agency for Health and Food Safety (AGES), Graz, Austria.
⁵ ZuchtData EDV-Dienstleistungen GmbH, Vienna, Austria.
⁶ Data, Statistics and Risk Assessment, Austrian Agency for Health and Food Safety (AGES), Graz, Austria.
⁷ Veterinary Practice, Parschlug, Austria.

Abstract

The aim of this study was to investigate the prevalence of ESBL/AmpC-producing E. coli and the resistance pattern of commensal E. coli, as well as the link between the use of antibiotics (AMU) and the occurrence of resistance in E. coli on Austrian dairy farms. AMU data from 51 farms were collected over a one-year period in 2020. Fecal samples were collected from cows, pre-weaned and weaned calves in 2020 and 2022. Samples were then analyzed using non-selective and selective agar plates, E. coli isolates were confirmed by MALDI-TOF analysis. Broth microdilution was used for antimicrobial susceptibility testing. The AMU of each farm was quantified as the number of Defined Daily Doses (nDDD_vet) and Defined Course Doses (nDCD_vet) per cow and year. Cephalosporins (mean 1.049; median 0.732 DDD_vet/cow/year) and penicillins (mean 0.667; median 0.383 DDD_vet/cow/year) were the most frequently used antibiotics on these farms, followed by tetracyclines (mean 0.275; median 0.084 DDD_vet/cow/year). In 2020, 26.8% of the E. coli isolated were resistant to at least one antibiotic class and 17.7% of the isolates were classified as multidrug resistant (≥3 antibiotic classes). Out of 198 E. coli isolates, 7.6% were identified as extended-spectrum/AmpC beta-lactamase (ESBL/AmpC) producing E. coli. In 2022, 33.7% of E. coli isolates showed resistance to at least one antibiotic and 20.0% of isolates displayed multidrug resistance. Furthermore, 29.5% of the samples carried ESBL/AmpC-producing E. coli. In 2020 and 2022, the most frequently determined antibiotic resistances among commensal E. coli isolates were to tetracyclines, sulfonamides and penicillins. In addition, pre-weaned calves had the highest resistance rates in both years. Statistical analyses showed a significant association between low and high use AMU classifications for penicillins (in nDDD_vet/cow/year) and their respective resistance among commensal E. coli isolates in 2020 (p = 0.044), as well as for sulfonamide/trimethoprim (p = 0.010) and tetracyclines (p = 0.042). A trend was also noted between the total amount of antibiotics used on farm in 2020 (by nDDD_vet/cow/year) and multidrug resistances in commensal E. coli isolated on farm that year (p = 0.067). In conclusion, the relationship between AMU and antimicrobial resistance (AMR) on dairy farms continues to be complex and difficult to quantify.

Keywords: ESBL; Escherichia coli; antibiotics; antimicrobial resistance; calves; cattle.