- LONDON - A clear link between the use of antibiotics in animal feed
and the emergence of "superbugs" in hospitals has been established
for the first time.
- Doctors have repeatedly warned of the
danger, but proving it has been more difficult. The emergence of antibiotic-resistant
strains of common bacteria is often blamed on excessive use of antibiotics
in medicine, rather than in animal feedstuffs.
- Now gene tests on bacteria in the gut
of people, pigs and chickens have shown that resistance to one particular
antibiotic has moved from animals to humans. The new studies, carried out
by Henrik Wegener of the Danish Veterinary Laboratory, suggest that a common
type of bacterium found in the intestine developed resistance to vancomycin,
a widely used antibiotic, when a similar drug was used in animal feed.
- Antibiotics are given in animal feed
because they typically increase the growth rate by 5 per cent. Dr. Wegener
now believes that they should be banned as growth promoters.
- Enterococci - bacteria in the gut - became
resistant to vancomycin in 1986, and the resistant forms spread throughout
Europe and the U.S. They are not usually dangerous except in patients with
poor immune systems, so these new strains have not caused as much alarm
as vancomycin-resistant Staphylococcis aureus, known as "superstaph,"
which has since begun to appear.
- Dr. Wegener showed that the resistance
moved from animals to humans by isolating the gene responsible for vancomycin
resistance in enterococci from people, pigs and chickens. He found that
the gene - apart from disarming vancomycin - contained a mutation.
- Bacteria in poultry from several countries
all carried one type of mutation, pigs carried another. Humans carried
- This means, says Dr. Wegener, that humans
must have got the resistance from animals. If the traffic had been in the
other direction, animals would show both variants.
- Avoparcin, the antibiotic used in animal
feeds, was banned in 1997, but animals are now being given another antibiotic,
virginiamycin, which is very similar to the new drug, Synercid, used to
replace vancomycin in human beings. Studies have already shown that some
enterococci in farm animals are resistant to Synercid. "The story
about avoparcin and vancomycin is rewriting itself," Dr Wegener told
- Roche Products, the company which makes
avoparcin, remains unconvinced. "These are interesting data, but I'm
not sure you can categorically state from them that it is one-way traffic
of resistance," said Dr. Tony Mudd, of Roche.