Analysis of Antimicrobial Use and the Presence of Antimicrobial-Resistant Bacteria on Austrian Dairy Farms—A Pilot Study

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.

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

“…The present study recorded a mean AMU value of 2.504 DDDvet/ cow/year (median 2.580; minimum 0.028 to a maximum of 6.910 DDD vet /cow/year). A previous study from Austria, using a comparable (39). By comparison, in 2007, a study conducted in the United States found that conventional dairy herds had an mean AMU of 5.43 DDD/cow/year (40).…”

“…Additionally, 22.5% of samples obtained from weaned calves were positive for ESBL/AmpC-producing E. coli. A previous study conducted in Austria in 2017 analyzed voided fecal samples from cowsheds, calf pens and youngstock housing areas, and found that 26% of dairy farms had ESBL/AmpC-producing E. coli present (39).…”

Current Insights Regarding the Role of Farm Animals in the Spread of Antimicrobial Resistance from a One Health Perspective

“…Several studies explored the selective effect of the level of AMU and the selection for AMR bacteria in farm animals. However, their results were not conclusive in most cases [60]. Indeed, no studies could demonstrate a significant selective effect on the intestinal population of E. coli following the use of colistin in pigs, whether used at therapeutic or at higher doses [61][62][63].…”

“…Indeed, no studies could demonstrate a significant selective effect on the intestinal population of E. coli following the use of colistin in pigs, whether used at therapeutic or at higher doses [61][62][63]. This was also not found for cephalosporin resistance mediated by extended-spectrum beta-lactamase (ESBL)-producing (ESBLs) E. coli strains of dairy herd origin [60,64].…”

Antibiotics in Dairy Production: Where Is the Problem?

“…Surprisingly, the relationship between the use of antibiotics in livestock and the presence of ARB in food has only been established indirectly and remains a contentious subject for study, which does not yield conclusive results [115,116]. This may be due, in part, to the lack of adequate models to study this relationship and because there is a poor understanding of the complex processes that lead to the emergence and spread of AR [115].…”