9 Resistance in animal pathogens

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Report highlights 2024:

Resistance in animal pathogens

Surveillance of antimicrobial resistance in 2024 focused on pathogenic bacteria from acute mastitis in dairy cows and from various organs in pigs and included results obtained through antimicrobial susceptibility testing.

Most pathogenic bacteria from acute mastitis in dairy cows displayed low frequencies of phenotypic resistance. A relatively high proportion of Streptococcus uberis isolates displayed resistance to penicillin, which is noteworthy because beta-lactamase sensitive penicillins are the most commonly used drugs for treatment of adult cattle in Denmark. However, there is currently no clinical breakpoint available for penicillin in S. uberis and most of the isolates had a MIC value of 0.25mg/L, which is just above the tentative ECOFF of 0.12 mg/L. Thus, it remains unclear whether penicillin is active against these borderline resistant S. uberis isolates.

Most pathogenic bacteria isolated from pigs in 2024 displayed similar frequencies of phenotypic resistance as in 2023 (1-year period) and 2019 (5-year period). However, six pathogen-drug combinations were associated with significantly increased resistance, whereas three were associated with significantly decreased resistance. The increased frequency of neomycin resistance in haemolytic Escherichia coli is worrisome because it is one of only a few drugs recommended in Denmark as first choice for treating E. coli-associated post-weaning diarrhoea. The increased frequency of gentamicin resistance in haemolytic E. coli is also worrisome because it is considered critically important for human medicine by the World Health Organization. It should also be noted that haemolytic E. coli displayed increased resis-tance to 3rd generation cephalosporins (cefpodoxime), from 4.7% in 2023 to 8.2% in 2024, although this change was nonsignificant.