9 Resistance in animal pathogens

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Report highlights 2023:

Resistance in animal pathogens

Surveillance of antimicrobial resistance in 2023 focused on pathogenic bacteria from pigs and included results obtained through antimicrobial susceptibility testing (AST) and/or whole genome sequencing (WGS) of isolates belonging to Actinobacillus pleuropneumoniae (AST and WGS), Bordetella bronchiseptica (AST and WGS), Clostridium perfringens (WGS), Erysipelothrix rhusiopathiae (WGS), haemolytic and non-haemolytic Escherichia coli (AST and WGS), Glaesserella parasuis (WGS), Klebsiella pneumoniae (AST and WGS), Salmonella enterica (AST and WGS), Staphylococcus hyicus (AST and WGS) and Streptococcus suis (AST and WGS).

Most pathogenic bacteria isolated from pigs in 2023 displayed similar frequencies of phenotypic resistance as in 2022 (1-year period) and 2018 (5-year period). However, nine pathogen-drug combinations were associated with significantly increased resistance, whereas one was associated with a significantly decreased frequency.

The increased frequency of neomycin resistance in haemolytic E. coli (52.3%) is concerning because it is one of only few drugs recommended in Denmark as first choice for treating E. coli-associated post-weaning diarrhea. The rapid increase in neomycin resistance coincided with increased use of neomycin in weaners.

The increased frequency of gentamicin resistance in haemolytic E. coli (35.2%) is also concerning because it is considered critically important for human medicine by the World Health Organization.

WGS-based detection of resistance mechanisms (genes and point mutations) in pathogenic bacteria isolated from pigs in 2023 showed that 22 pathogen-resistance mechanism combinations were associated with significantly increased frequencies when compared to 2022 (1-year period) and 2021 (2-year period), whereas one was associated with a significantly decreased frequency.

Resistance towards carbapenems, 3rd, 4th and 5th generation cephalosporins, oxazolidinones and polymyxins remained at a low level.

The observed concordance between AST results and WGS-based detection of resistance mechanisms was 99.6% for A. pleuropneumoniae, 79.6% for B. bronchiseptica, 94.2% for haemolytic E. coli, 94.3% for non-haemolytic E. coli, 76.0% for K. pneumoniae, 97.3% for S. enterica, 91.5% for S. hyicus and 94.5% for S. suis.