7 Resistance in indicator bacteria
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Report Highlights 2023:
Resistance in indicator bacteria
Over the last five-year monitoring period, there have been no statistically significant trends in the prevalence of fully sensitive indicator E. coli from broilers or pigs. However, in the same period, there was a significant decrease in fully sensitive E. coli from cattle.
As in previous years, no colistin, meropenem or tigecycline resistance were detected in indicator E. coli. Amikacin resistance was detected in single isolates from broilers and pigs. Resistance to ciprofloxacin continued to be low in cattle and pigs, and after the increase observed in the previous year, it has decreased by 3% in broilers. Similarly to 2022, in 2023, azithromycin resistance was detected in a small number of isolates from pigs (3%) and additionally in 2% of broiler isolates. Additionally, in cattle, increases between 2% and 7% were observed in the resistance to ampicillin, chloramphenicol, sulfamethoxazole, tetracycline and trimethoprim.
The relative occurrence of multidrug-resistant indicator E. coli compared to the previous year increased in broilers and cattle, however a significant increasing trend over the past five years was only detected for cattle. Combined resistance to ampicillin, sulfamethoxazole, and tetracycline (ASuT) continued to be the most common multidrug-resistance profile among E. coli from cattle and pigs, however the relative occurrence of other profiles has increased in isolates from cattle in the past five years.
Importantly, as in previous years, samples from pigs, cattle and their meat examined for carbapenemase-producing (CP) E. coli (including OXA-48) were found negative.
The occurrence of beta-lactamase-producing E. coli, obtained through selective procedures, continued the decreasing trend observed since 2019 in Danish cattle and pigs, and in imported pork, and was also lower in beef (domestic and imported) in 2023, compared to 2021. Antimicrobial susceptibility testing of ESBL-/AmpC-producing E. coli from imported beef showed, like in previous years, a very high (100%) occurrence in resistance to fourth generation cephalosporins (cefepime). Isolates from pigs and pork (domestic and imported) showed a decrease in occurrence of resistance to cefepime, compared to 2021. A single isolate from imported pork was found resistant to ertapenem, while one isolate from cattle and three isolates from pigs were found resistant to imipenem.
Whole genome sequencing of beta-lactamase-producing E. coli revealed ESBL, AmpC and ESBL+AmpC genotypes. All but one AmpC genotypes encoded upregulated AmpC promotor C-42T mutations, which was also observed in two ESBL+AmpC genotypes, one from pigs and another from cattle. Among the ESBL genotypes, 11 different ESBL genes were detected, with the most frequent being CTX-M-1 and CTX-M-15.
In 2023, 22% of E. faecalis isolated from pigs were fully sensitive. None of the isolates showed resistance to ampicillin, ciprofloxacin, linezolid, teicoplanin, tigecycline or vancomycin. Combined resistance to chloramphenicol, tetracycline and erythromycin was the most common resistance profile. The overall decrease in resistance observed in 2021 did not continue in 2023.