Pigs and other farm animals are harbouring major reservoirs of
antibiotic-resistant bacteria, according to research presented today
(Wednesday, 08 September 2004) at the Society for General
Microbiology's 155th Meeting in Trinity College Dublin, by researchers
from the University of Leeds.
The scientists were concerned
about the effects that decades of use of antibiotics to treat
infections, prevent diseases, or promote growth, have had on the spread
of antibiotic resistance genes in common farm bacteria.
"The European Commission banned some growth promoting antibiotics in
1999, and all growth promoters will be banned by 2006," says Melanie
Thompson of the School of Biochemistry and Microbiology at Leeds
University. "But the use of these antibiotics in animal husbandry for
many years to treat illness, prevent infections and increase the growth
rate and food efficiency of the animals has exerted a Darwin-style
selective pressure on the different types of bacteria which survive in
farm animals. For years we have been actively selecting for bacteria
which possess genes capable of antibiotic resistance."
countries the effect of a ban on growth-promoting antibiotics has been
an increase in their use as veterinary medicines, meaning that their
overall use hardly alters. The antibiotics used for animals are either
structurally very similar or identical to ones used in human medicine.
If resistant bacteria from farm animals pass through the food chain to
infect people, some commonly used antibiotics for human medicine could
become ineffective, and people could suffer infections which would not
respond to conventional therapies.
Bacteria originally from food
animals can reach people through poor hygiene, improper food handling
and inadequate cooking. The scientists looked at the types of bacteria
and the antibiotic resistance they already possess at a commercial pig
farm to assess the probability of resistant bacteria being present in
food intended for human consumption.
"We found that some of
the bacteria taken from pig faeces could easily transfer resistance
genes to laboratory bacteria," says Melanie Thompson. "This was not
surprising, but it is worrying, since if bacteria can transfer genes in
a laboratory, they are likely to be able to do it in other enclosed
places, such as inside the human gut."
The research team is
now looking at different samples taken from different groups of pigs
ranging in age from their farrowing to their finishing to see how the
bacteria which contaminate them change. The groups will also be exposed
to different farming practices to find out if this alters the types of
bacteria they are carrying.
The scientists have so far looked at
40 different samples of bacteria from pigs and discovered resistance
genes to tetracyclines, ciprofloxacin, and ampicillin, although so far
no resistance has been found to extended-spectrum cephalosporins.
Society for General Microbiology. August 2004.