Abstract
The assumed link between high levels of antimicrobial use on farms and selection for antimicrobial-resistant (AMR) bacteria on that farm remains difficult to prove. In the pilot study presented here, we analysed total antimicrobial use on 50 dairy farms in Austria and also collected environmental samples to ascertain whether specific AMR bacteria were present. Antimicrobial use (AMU) analysis was based on electronic veterinary treatment records over a one-year period. Faecal samples for the assessment of extended-spectrum beta-lactamase (ESBL)-producing E. coli were collected from cowsheds, calf pens, and youngstock housing areas, as well as dust samples from barns, to isolate methicillin-resistant Staphylococcus aureus (MRSA). Bacteriological cultures were carried out on selective agar. Farms were split into groups of 25 of the highest antimicrobial users and 25 of the lowest users. Overall, samples from 13/50 (26.0%) farms were found to be positive for the presence of ESBL-producing E. coli. Of these, eight farms were in the low user group and five were in the high user group. Only one farm was confirmed to harbour MRSA. Statistical analyses demonstrated that there was no significant difference in this study population between high or low antimicrobial use with respect to the presence of ESBL-producing E. coli on farms (p = 0.33). In conclusion, the presence of specific AMR bacteria on farms in this study population was not found to have a statistically proven relationship with their level of antimicrobial use.
Highlights
The excessive use of antimicrobials and the increasing level of antimicrobialresistant bacterial infections in both humans and animals are continuing to cause concern among veterinarians, medics, and the general public [1]
138 voided faecal samples were collected from 50 farms (25 classified as “high” antimicrobial users and 25 as “low” users)
The results presented here did not show a relationship between the presence of extended-spectrum beta-lactamase (ESBL)-producing E. coli and the use of third and fourth generation cephalosporins, contrasting with a Dutch study which found the use of these highest priority critically important antimicrobials (HPCIAs) led to an 8.05-fold increase in the odds of testing positive for ESBL/AmpC-producing E. coli [9]
Summary
The excessive use of antimicrobials and the increasing level of antimicrobialresistant bacterial infections in both humans and animals are continuing to cause concern among veterinarians, medics, and the general public [1]. Total Antimicrobial Use in Defined Daily Dose (DDDvet/Cow/Year). Intramammary treatments were calculated slightly differently, as the European Medicines Agency classes each udder tube as 1 DDDvet, regardless of milligrams of active substance or standardised cow live weight (for details, see [21,44]). DDDvet values have not been assigned by the EMA for dry cow therapy (DCT) intramammary tubes, only Defined Course Doses (DCDvet). For this reason, DCT was excluded from the majority of the AMU analyses included here. As dry cow therapy is an important part of the antimicrobial use statistics of dairy farms, a comparison of the corrected DCDvet/cow/year was carried out between those farms testing positive for the presence of ESBL-producing E. coli and those testing negative. The DCD/cow/year value was corrected by the replacement rate and calving interval for each of the farms included here, as described elsewhere [53]
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