As the recent U.S. outbreak of E. coli infections
caused by contaminated spinach demonstrates,
the safety of the food we eat cannot be taken
for granted. Two studies in the Nov. 1 issue
of The Journal of Infectious Diseases, now
available online, further illustrate the point,
one adding a new bacterial culprit to the
mix and the other showing that use of antibiotics
as growth promoters in livestock increases
the risk of antibiotic resistance in humans.
In one study, investigators led by Katri
Jalava, DVM, of the Finnish National Public
Health Institute, and J. Pekka Nuorti, MD,
DSc, of the National Centers for Disease Control
and Prevention, traced an outbreak of Yersinia
pseudotuberculosis infection among children
in a Finnish town to carrots grown on a single
farm. An epidemiologic investigation linked
illness to eating raw carrots. Laboratory
tests confirmed that the bacteria in infected
children's stool samples were indistinguishable
from the bacteria isolated from the farm.
The authors noted that this marked the first
time that the bacterium had been recovered
from an epidemiologically implicated source
of food-borne illness. They pointed out that
it is well known as a pathogen in wild mammals,
and that the farm stored the carrots in a
barn in open containers for months. "A combination
of direct contact with wildlife feces during
storage and cross-contamination during washing
and peeling," they concluded, "are the most
likely contributing factors." To prevent such
outbreaks, "regulations addressing the production,
storage and shipping conditions for fresh
produce are needed."
In the other study, Edward A. Belongia, MD,
and colleagues at the Marshfield Clinic Research
Foundation, Marshfield, Wis., and elsewhere
examined poultry exposure as a risk factor
for antibiotic resistance by Enterococcus
faecium, a gut bacterium that is an increasing
cause of hospital infections. A drug combination
called quinupristin-dalfopristin, also known
as Synercid, is used to treat serious E. faecium
infections that are resistant to the first-choice
antibiotic. Synercid is related to virginiamycin,
an antibiotic that has long been used as a
growth promoter in U.S. livestock but is now
banned in Europe. The question Dr. Belongia
and colleagues asked was, does exposing poultry
to virginiamycin lead to Synercid-resistant
E. faecium in humans?
The group isolated E. faecium in stool samples
from 105 newly hospitalized patients and 65
healthy vegetarians, and in 77 samples of
conventional retail poultry and 23 antibiotic-free
poultry meat samples.
Laboratory tests showed that 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. 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.
In an editorial commenting on the studies,
Niels Frimodt-Møller, MD, DMSc, and Annette
M. Hammerum, PhD, MSc, of the Danish National
Center for Antimicrobials and Infection Control,
observed that the findings are "examples of
how industrialization of food production …carries
and even amplifies risk for unaware consumers."
To reduce or remove the risk of food contamination
as documented by the Finnish team, they noted,
requires multiple measures at multiple levels,
such as growing and storing carrots away from
animals and encouraging hygienic practices
for harvesters and harvesting machinery. To
reduce or remove the risk of resistant gut
bacteria, however, the editorial authors say
the answer is easy: "Ban antibiotic growth
promoters!"
