Ellen
Silbergeld, Eng ’72 (PhD), recalls that she did not want to
go to the seminar. She was a professor of epidemiology at
the University of Maryland School of Medicine in 1999 when
her department’s chairman needed an audience for the
seminar’s presenter, a candidate for a faculty position.
Silbergeld recalls the chairman saying, “Please, just sit
in the room. You can come to lunch.” So she sat in the
room, and something caught her attention. The seminar was
on hospital-acquired infections, but the presenter
mentioned in passing that some drug-resistant infections
came from food. That seemed odd. Silbergeld knew you could
pick up

Salmonella from, say, tainted chicken salad.
But how would that

Salmonella have become resistant
to antibiotics? She turned to a colleague and asked.
Because, he said, factory chicken farms routinely feed
antibiotics to their flocks, to accelerate growth, and the
drugs generate resistance.

Ten years later, Silbergeld, now a professor of
environmental health sciences at the Bloomberg School of Public
Health
, is one of several researchers at Johns Hopkins
and around the world assembling evidence that the
industrial farming of chickens, pigs, and cattle is
cultivating more than poultry and livestock — it’s
cultivating bacteria that medicine is losing the ability to
fight. Antimicrobial drugs, including antibiotics like
penicillin, ciprofloxacin, and methicillin, kill pathogenic
bacteria. But they simultaneously drive the resistance that
is bacteria’s defense, especially when administered in low,
subtherapeutic doses. Scientists estimate that 50 percent
to 80 percent of all antimicrobials in the United States
are not used by doctors to treat sick people or animals but
are added to farm animal feed, mostly in such
subtherapeutic dosages. Public health researchers like
Silbergeld are convinced that this nontherapeutic use of
antimicrobials is building dangerous genetic reservoirs of
resistance. If they are right, industrial agriculture is
fostering and dispersing drug-resistant bacteria that
impair medicine’s ability to protect the public from
them.

The United States Department of Agriculture (USDA)
estimates that livestock and poultry produce 335 million
tons of manure per year, which is one way resistant
pathogens get out of animals and into the environment.
That’s 40 times as much fecal waste as humans produce
annually. Farms use it for fertilizer and collect it in
sheds and manure lagoons, but those containment measures do
not prevent infectious microbes from getting into the air,
soil, and water. They can be transported off the farms by
the animals themselves, houseflies, farm trucks, and farm
workers, and by spreading manure on other fields. Out in
the environment, they form a sort of bank of genetic
material that enables the spread of resistance.