[pf] soil bacteria acquiring tetracycline-resistance genes: Univ of IL

· I have never understood why "farmers" have to use antibiotics with
_well_animals_. I know there are economic "justifications" (perhaps faster
growth, certainly an attempt to counter the negative effects of having what
should be free-range animals in "factories"_feed-lots).

· I don't accept that economic reasons are justifications on their own.
Particularly when antibiotic resistance has been predicted for so long. Of
course, antibiotic resistance affects _others_, now and in the future, so
is another "externality" to be ignored.

· This is a report from the University of Illinois at Urbana-Champaign.
     D.

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http://www.newscientist.com/dailynews/news.jsp?id=ns9999640
  is:

Spreading problem
Superbug genes are getting into soil and water - will humans be next? 

Exclusive from New Scientist magazine 

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' 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. 


Broad ecological presence


"This is very important. [The study] is the first of its kind to
demonstrate this kind of broad ecological presence of tetracycline
resistance genes," says Stuart Levy, director of the Center for Adaptation
Genetics and Drug Resistance at Tufts University in Boston.

"And 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."

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 Scientists, a
non-profit organisation based in Cambridge, Massachusetts.


Drinking water


To study the environmental effect of these antibiotics around two swine
farms that use tetracycline as a growth promoter, Aminov's 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' guts. This strongly suggests that the bacteria
from the pigs are transferring their genes to the ones outside, says Aminov.

"People 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," he says. And as groundwater accounts for a substantial part
of the public water supply in the US, the problem could be widespread. 


On the increase


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. 

"What we are seeing here is that if a resistance gene gets out into the
bacterial population in nature, it's 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," she says.

More at: Applied & Environmental Microbiology (vol 67, p 1494)

Correspondence about this story should be directed to: 
letters@newscientist.com 

1900 GMT, 18 April 2001

Anil Ananthaswamy


© Copyright New Scientist, RBI Limited 2001

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