2.2.3 Monitoring indicator bacteria from healthy animals

Now let’s look at monitoring indicator bacteria from healthy animals, whose presence is monitored because it can give an indication of the magnitude of the AMR problem.

E. coli and Enterococcus spp. can serve as indicators of resistance in an animal population because they:

• are present as commensals in the gut microbiota of healthy animals and humans
• can acquire AMR both via mutations in chromosomal genes and horizontal transfer of ARGs
• have the potential to cause infections in both animals and humans, and to transfer AMR to pathogenic bacteria of the same or other species.

Monitoring the prevalence of acquired resistance in such commensal bacteria can indicate the magnitude of selective pressure from the use of antimicrobials in an animal population.

For example, monitoring resistance in indicator bacteria such as E.coli has been conducted in Denmark since 2010 in broiler chickens, cattle and pigs. Figure 7 shows that the occurrence of ampicillin, sulfonamide, tetracycline and trimethoprim resistance was significantly higher in E. coli from pigs compared with isolates from cattle and broilers. In contrast, resistance to ciprofloxacin in isolates from broilers (red in the figure) was higher than in isolates from cattle and pigs, and it continues a slow but increasing trend. All antimicrobials in the figure are also used in human health.

This information has been used to assess the zoonotic risk linked to transfer of resistance to critically important antimicrobials from animals to humans. You can read more about the interpretation and usefulness of data in Section 7.2.2 of the DANMAP report [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] (Korsgaard et al., 2020). This information is routinely compared to reports from other EU member states to understand the trends.

Maximise

Figure 7 Resistance (%) among Escherichia coli isolates from broilers (top left), cattle (top right) and pigs (below) in Denmark – all the isolates were obtained from the caeca at the abattoirs. The number of isolates appear in parenthesis.

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There is a variety of resistance in broilers between 0 and 30%. Resistance among all isolates in cattle is less than around 10%. Resistance in cattle varies: some isolates are between 20 and 40%, while others are around 5% or lower.

Figure 7 Resistance (%) among Escherichia coli isolates from broilers (top left), cattle (top right) and pigs (below) in Denmark – all ...