Researchers at the
Johns Hopkins Bloomberg School of Public Health have
found evidence that
houseflies collected near broiler poultry operations may
contribute to the dispersion of drug-resistant
bacteria and thus may increase the potential for human
exposure to drug-resistant bacteria.
The findings demonstrate another potential link
between industrial food animal production and
exposures to antibiotic-resistant pathogens. Previous
studies have linked antibiotic use in poultry
production to antibiotic-resistant bacteria in farm
workers, consumer poultry products and the
environment surrounding confined poultry operations, as
well as to releases from poultry transport.
"Flies are well-known vectors of disease and have been
implicated in the spread of various viral
and bacterial infections affecting humans, including
enteric fever, cholera, salmonellosis,
campylobacteriosis and shigellosis," said lead author Jay
Graham, who conducted the study as a
research fellow with the Bloomberg School's
Center for a Livable
Future. "Our study found similarities
in the antibiotic-resistant bacteria in both the flies and
poultry litter we sampled. The evidence is
another example of the risks associated with the inadequate
treatment of animal wastes."
Added Ellen Silbergeld, senior author of the study and
professor in the Bloomberg School's
Department of Environmental Health Sciences, "Although we
did not directly quantify the contribution
of flies to human exposure, our results suggest that flies
in intensive production areas could
efficiently spread resistant organisms over large
distances."
Graham and his colleagues collected flies and samples
of poultry litter from poultry houses
along the Delmarva Peninsula, a coastal region shared by
Maryland, Delaware and Virginia that has one
of the highest densities of broiler chickens per acre in
the United States. The analysis by the
research team isolated antibiotic-resistant enterococci and
staphylococci bacteria from both flies and
litter. The bacteria isolated from flies had very similar
resistance characteristics and resistance
genes to bacteria found in the poultry litter.
Flies have ready access to both stored poultry waste
and to poultry houses. A study by
researchers in Denmark estimated that as many as 30,000
flies could enter a poultry house over the
course of a six-week period.
Additional authors of the study are Lance Price, Sean
Evans and Thaddeaus Graczyk. The study
is published in the April issue of Science of the Total
Environment. The research was funded by a
grant from the Johns Hopkins Center for a Livable
Future.
According to Robert Lawrence, director of the Center
for a Livable Future, confined animal
feeding operations — where thousands of animals are
crowded together and are fed antibiotics for
growth promotion — create the perfect environment for
selection of bacteria that are resistant to
antibiotics. "Antimicrobials are among the most important
developments of the 20th century in
managing infectious diseases in people. We can't afford to
squander them by using them as growth
promoters in industrial food animal production," Lawrence
said. "The increase in antibiotic-resistant
bacteria is a major threat to the health of the public, and
policy-makers should quickly phase out and
ban the use of antimicrobials for nontherapeutic use in
food animal production."
GO TO