Antibiotic use as a livestock growth promoter
increases the risk of human antibiotic resistance,
a Marshfield Clinic researcher and his colleagues
have found.
Results of the nearly $1.4 million three-year
study, funded by the Centers for Disease Control
and Prevention, Atlanta, Georgia, are in the
November 1 issue of The Journal of Infectious
Diseases.
Edward Belongia, M.D., Marshfield Clinic
Research Foundation, Marshfield, Wis., and
his colleagues examined poultry exposure as
a risk factor for antibiotic resistance in
Enterococcus faecium, a gut bacterium that
is increasingly the cause of infections in
hospitals. The investigation team focused
on use of a growth-promoting antibiotic, called
virginiamycin, in poultry.
Virginiamycin is closely related to quinupristin-dalfopristin,
an antibiotic licensed to treat patients with
serious, antibiotic-resistant infections.
The drug is prescribed under the brand name
Synercid. According to Belongia, "There is
a relative lack of data on the impact of antibiotic
use in livestock and its relationship to antibiotic
resistance in humans, but there is a fair
amount of indirect evidence suggesting that
antibiotic use could pose a risk to human
health."
"We've known for a long time that resistant
bacteria can be found on retail poultry products,
but our study is one of the first to show
an association between human carriage of antibiotic
resistance genes and eating poultry or handling
raw poultry.
"These results indicate that virginiamycin
use in poultry leads to transfer of antibiotic
resistance genes to human gut bacteria through
the food supply and they provide additional
evidence that use of growth promoters in animals
may have long-term consequences for human
health. The Food and Drug Administration (FDA)
can use this information to improve its risk
assessment procedures."
The importance of this issue was illustrated
by a recent FDA Veterinary Medicine Advisory
Committee meeting about an application to
license a broad spectrum antibiotic, called
cefquinome, for use in cattle. Belongia spoke
at the hearings, representing the Infectious
Diseases Society of America.
"There was a great deal of concern that this
antibiotic could promote resistance to cephalosporin
drugs that are essential for many patients
with serious or life-threatening infections,"
Belongia said, "and at the end of the day
the FDA committee recommended against the
drug. Our study focused on a different drug
in a different type of animal, but this is
a timely example of the controversy regarding
the appropriate use of antibiotics in food-producing
animals.
"We need to have drugs to treat sick animals,"
he added, "but we should not be using antibiotics
to promote growth."
Working with Belongia, as principal investigator,
were members of the Marshfield Enterococcal
Study Group - Amy L. Kieke, Ph.D., Mark A.
Borchardt, Ph.D., Burney A. Kieke, Susan K.
Spencer and Mary F. Vandermause; and Minnesota
Department of Health, St. Paul, Minnesota
- Kirk E. Smith and Selina L. Jawahir. Amy
Kieke was the first author on the published
paper. Borchardt directed laboratory activities
to detect antibiotic resistance and resistance
genes. Belongia and colleagues posed the question:
Does exposing poultry to virginiamycin lead
to Synercid-resistant E. faecium in humans?
They isolated E. faecium in stool samples
from 105 newly-hospitalized patients and 65
healthy vegetarians, as well as in 77 samples
of conventional retail poultry and 23 antibiotic-free
poultry meat samples.
After exposure to virginiamycin, E. faecium
from conventional poultry and from patients
who consumed poultry became resistant to Synercid
more often than E. faecium from vegetarians
or from antibiotic-free poultry. Some of the
resistance was attributed to a specific gene
and both the gene and resistance were associated
with touching raw poultry meat and frequent
poultry consumption.
Laboratory tests showed the bacteria isolated
from patients and vegetarians had no pre-existing
resistance to Synercid. Resistance was rare
among antibiotic-free poultry but a majority
of bacterial isolates from conventional poultry
samples were resistant.
