Unfortunately, Denmark’s comprehensive reform of antibiotic use in
agriculture doesn’t necessarily mean Danes are safe from
antibiotic-resistant pathogens carried in animals or meat. That’s
illustrated by recent work40 by Yvonne Agersø tracking the emergence of
bacteria that carry a gene for the production of extended spectrum
β-lactamase (ESBL) enzymes, which confer resistance to both penicillins and
cephalosporins.
Cephalosporins have been widely used as growth promoters in chickens in some
parts of the world, but were never used on Danish poultry. Yet recent data
show a dramatic rise in the incidence of ESBL-producing Escherichia coli
bacteria in chicken meat sold in Denmark. In 2012 testing showed that 61% of
samples of imported chicken were contaminated with ESBL-producing E. coli,
but the same kinds of microbes also were identified in 36% of samples from
poultry raised in Denmark, even though the chickens had never received
cephalosporins.41
Agersø and her colleagues tracked the resistant microbes back through
generations of birds.40
The grandparents of the contaminated Danish chickens had been imported from
Scotland, where they were treated with cephalosporins very early in life,
and resistant bacteria passed from one generation to the next. A Swedish
team recently reported similar findings for chickens in that country.42 The findings point up the
need for international standards restricting the agricultural use of
antibiotics.