Antibiotics
in the ecosystem
The Environmental
Impact of Antibiotics
... A public awareness campaign
The
Role of Bacteria
Bacteria
are microorganisms that are found on our skin, in our digestive
tract, in the air, in soil, and on almost all the things we
touch every day. Most are harmless (non-pathogenic). Many are
helpful because they occupy ecological niches (both within our
bodies and in the external environment) that could be occupied
by harmful (pathogenic) bacteria. These helpful strains keep
harmful microorganisms in check. They also help our digestion
to function effectively and stimulate the development of a healthy
immune system.
The
Use of Antibiotics
Antibiotics
used to treat infections are an invaluable tool, and their introduction
revolutionized the treatment of infectious disease. However,
in addition to being used to treat human disease, they have
other applications. In the United States roughly half are used
in non-human applications. Large amounts are employed in both
plant and animal farming. In animals, antibiotics are used to
prevent infection as well as to treat disease. Smaller doses
are added to animal feed to promote growth. Antibiotics, chiefly
streptomycin and oxytetracycline, are used to control bacterial
infections of fruits and vegetables. Because of their wide-spread
use, it is not surprising that antibiotics have been found in
liquid waste at animal feedlots, and have spread into many surface
and ground water supplies.
Antibacterial
Resistance and the Environment
The ubiquitous
presence of antibiotics has upset the delicate balance of microorganisms
in the environment. Over millions of years, bacteria have evolved
a number of strategies to coexist peacefully, including the
capacity to produce antibiotics to ward off competitors. Other
organisms have an ability to destroy these substances programmed
into their genetic makeup, and having this capacity, are said
to be antibiotic resistant. Both types have always existed.
However, before the wide-spread use of antibiotics, resistant
strains were a small fraction of the microorganism ecosystem.
Significant change has occurred with the large scale human uses
of antibiotics because these substances kill off antibiotic
susceptible bacteria, and thus create favorable environments
for the overgrowth of resistant strains.
As antibiotics become more widely used, resistant strains of
both harmful and harmless bacteria are replacing antibiotic
susceptible bacteria. Furthermore, resistant bacteria in one
environment may not be confined to that specific environment,
but can be carried thousands of miles away by wind, water, animals,
food, or people. And, most importantly, antibiotic resistant
organisms that develop in animals, fruits, or vegetables can
be passed to humans through the food chain and environment.
All of these factors have had the effect of changing the balance
between antibiotic susceptible and the antibiotic resistant
bacteria in our ecosystem, locally and globally.
Future
Implications of Antibacterial Resistance
Further
compounding the problem is that harmless bacteria with resistance
genes can transfer these genes to pathogenic bacteria that enter
the same environment. The genetic elements that are transferred
often carry factors that impart resistance to more than one
type of antibiotic. When such genetic elements are transferred,
they create "superbugs" that are resistant to many distinct
antibiotics. More and more frequently, we are seeing outbreaks
of dangerous infections caused by such superbugs. Over the past
few decades, the use of antibiotics has enabled us to control
many serious infectious diseases. However, as resistant strains
become more widespread due to natural and inevitable evolutionary
adjustments, antibiotics will cease to be the effective tool
they have been for physicians and patients to control infectious
diseases.
The
Project
In 1998,
APUA received a two-year grant from the Nathan Cummings Foundation
to support a national public awareness campaign. The campaign
is intended to increase public awareness of the need for responsible
use of antibiotics, and to improve the ecological balance of
resistant and susceptible strains of bacteria, both in the human
health care setting and in the overall environment. The objectives
of the project are to describe, quantify, and document the cumulative
selective force of various antibiotic uses in the environment
(plants, animals and humans) on the emergence of antibiotic
resistance; to disseminate this information to the public, the
press, and policy makers in order to lessen the misuse of antibiotics;
and to document links between antibiotic use in a species and/or
geographical areas and the emergence of resistant bacteria in
adjacent or related species or areas.
Antibiotics
kill more than the disease-causing bacteria to which they are
directed. They kill any other susceptible bacteria. Once the
ecosystem is cleared of susceptible bacteria, resistant bacteria
can multiply and dominate the environment due to lack of competition.
The phenomenon can be likened to weeds that have overgrown a
lawn where the grass has been completely destroyed by an overdose
of herbicides (Illustration by Bonnie Marshall, from The
Antibiotic Paradox, 2nd edition by Stuart B. Levy).
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