The presence of drug-resistant pathogenic bacteria on
uncooked poultry products varies by commercial brand and is
likely related to antibiotic use in production, according
to researchers at the
Johns Hopkins Bloomberg School of Public Health.
Their study is the first to directly compare bacterial
contamination of poultry products sold in U.S. supermarkets
from food producers who use antibiotics and from those who
claim they do not. The study focused on antibiotic
resistance, specifically fluoroquinolone-resistance in
Campylobacter, a pathogen responsible for 2.4 million cases
of food-borne illness per year in the United States,
according to the Centers for Disease Control and
Prevention. The study is published online in the journal
Environmental Health Perspectives.
"Our use of medically important classes of antibiotics
in food-animal production creates a significant public
health concern," said the study's lead author, Lance Price,
a doctoral candidate and fellow at the school's
Center for a
Livable Future. "Companies that use antibiotics foster
the development of drug-resistant bacteria which can spread
to the human population. Claims have been made that using
antibiotics increases food safety by reducing pathogens on
the meat. Interestingly, in addition to the results
regarding fluoroquinolone-resistant Campylobacter, we also
found that brands that do not use any antibiotics during
production were no more likely to contain Campylobacter
than those that do. In fact, the only brand with a
significantly lower rate of Campylobacter contamination was
actually an antibiotic-free brand."
Price said that previous epidemiological studies have
indicated that fresh poultry products are a major source of
Campylobacter infections in humans. Exposure can occur from
undercooked products or through cross-contamination during
food preparation, when raw poultry is handled in the
kitchen. The danger of infection is heightened when this
pathogen is resistant to antibiotics. Not only can the
bacteria itself cause illnesses such as diarrhea in humans,
but fluoroquinolones are some of the most important drugs
used to treat a variety of infections, including those
caused by Campylobacter. The widespread presence of this
drug-resistant form of the bacteria makes the antibiotic
less effective in human medicine. Especially vulnerable are
the very young, the elderly and people whose immune systems
are compromised.
In 2000, the Food and Drug Administration proposed to
withdraw approval of fluoroquinolone drugs for use in
poultry production. That effort has since been stalled by
legal objections from Bayer, one of the pharmaceutical
companies manufacturing the drug. In the meantime, two
major U.S. poultry producers, Tyson Food and Perdue Farms,
announced separately in 2002 that they would immediately
stop using fluoroquinolones to treat their flocks.
One year after the Tyson and Perdue announcements,
Price and his team began a survey of Campylobacter isolates
on uncooked chicken products from Tyson and Perdue and from
two other producers, Eberly and Bell & Evans, who claim
their production methods are completely antibiotic-free.
Using both standard isolation methods and new methods
modified to enhance detection of fluoroquinolone-resistant
Campylobacter, they compared retail products purchased at
grocery stores in Baltimore. A high percentage of the
products from the two conventional brands were contaminated
with fluoroquinolone-resistant Campylobacter (96 percent
from Tyson and 43 percent from Perdue) while significantly
lower proportions of 'antibiotic-free' products were
contaminated with fluoroquinolone-resistant Campylobacter
(5 percent from Eberly and 13 percent from Bell &
Evans).
"These results suggest that fluoroquinolone-resistance
may persist in the food supply for a substantial period of
time even after antibiotic use is discontinued," Price
said. "Assuming that what we are observing are lingering
resistant strains rather than the result of continued drug
use, then one has to conclude that fluoroquinolone use in
poultry production presents a long-term threat to
people."
The study, co-authored by E. Johnson, R. Vailes and E.
Silbergeld, was supported by the Johns Hopkins Center for a
Livable Future and by the Heinz Family Foundation.