快猫短视频

FARMERS should stop using antibiotics as growth promoters, say researchers in
the US. They have uncovered evidence of a new route by which dangerous
antibiotic resistance genes can spread.

There is already strong evidence that feeding animals antibiotics can lead to
the emergence of resistant strains of gut bacteria such as salmonella, which can
then be passed on to people in food or through direct contact with animals. Now
microbiologist Rustam Aminov of the University of Illinois at Urbana-Champaign
and his colleagues have discovered that bacteria in the soil and groundwater
beneath farms seem to be acquiring tetracycline resistance genes from bacteria
originating in pigs鈥� guts.

Once transferred, the resistance genes can persist in the hardier soil and
water-borne bacteria and could be passed on to potentially dangerous bacteria in
the environment, or in humans who drink the water. 鈥淭his is very important. [The
study] is the first of its kind to demonstrate this kind of broad ecological
presence of tetracycline resistance genes,鈥� says Stuart Levy, director of the
Center for Adaptation Genetics and Drug Resistance at Tufts University in
Boston.

鈥淎nd this is just tetracycline. Add all the other drugs that might be there,
and then I think it further supports the notion that we should be prudent in how
we use antibiotics in animals and people.鈥�

While the European Union has banned the use as growth promoters of most
antibiotics that are used in human medicine, farmers in the US still routinely
add antibiotics such as tetracycline, penicillin and streptomycin to livestock
feed to promote animal growth. Nearly 70 per cent of all antibiotics produced in
the US are fed to animals as growth promoters, according to the Union of
Concerned 快猫短视频s, a non-profit organisation based in Cambridge,
Massachusetts.

To study the environmental effect of these antibiotics around two swine farms
that use tetracycline as a growth promoter, Aminov鈥檚 team analysed samples from
farm-waste lagoons and from groundwater reservoirs beneath the lagoons. They
found that bacteria in the soil and groundwater carried tetracycline resistance
genes, or tet genes, that were almost identical to those in bacteria
living in the pigs鈥� guts. This strongly suggests that the bacteria from the pigs
are transferring their genes to the ones outside, says Aminov.

鈥淧eople at both sites are drinking this groundwater without any treatment.
This may be a new way of increasing the local concentration of antibiotic
resistance genes and circulating them between animals, humans and the
environment,鈥� he says. And as groundwater accounts for a substantial part of the
public water supply in the US, the problem could be widespread.

Abigail Salyers, also at the University of Illinois, agrees. She and her
colleagues recently showed that bacteria passing through human intestines
exchange genes with the resident bacteria. They found that 80 per cent of the
strains of a major bacterial species found in the colons of people in the late
1990s carried tetracycline resistance genes, compared with 30 per cent before
1970.

Together, the studies suggest that antibiotic resistance genes are being
transferred from the environment into our bodies, she says. 鈥淲hat we are seeing
here is that if a resistance gene gets out into the bacterial population in
nature, it鈥檚 like letting the genie out of the bottle. So far it looks like
there are very few, if any, limits to how far a resistance gene can spread,鈥� she
says.