About Antimicrobial Resistance: A Brief Overview
Antibiotics and similar drugs, together called antimicrobial agents, have been used for the last 70
years to treat patients who have infectious diseases. Since the 1940s, these drugs have greatly reduced
illness and death from infectious diseases. Antibiotic use has been beneficial and, when prescribed
and taken correctly, their value in patient care is enormous. However, these drugs have been used so
widely and for so long that the infectious organisms the antibiotics are designed to kill have adapted
to them, making the drugs less effective. Many fungi, viruses, and parasites have done the same. Some
microorganisms may develop resistance to a single antimicrobial agent (or related class of agent),
while others develop resistance to several antimicrobial agents or classes. These organisms are often
referred to as multidrug-resistant or MDR strains. In some cases, the microorganisms have become so
resistant that no available antibiotics are effective against them.
Drug Resistance Is Everywhere
Antimicrobial drug resistance occurs everywhere in the world and is not limited to industrialized
nations. Hospitals and other healthcare settings are battling drug-resistant organisms that spread
inside these institutions. Drug-resistant infections also spread in the community at large. Examples
include drug-resistant pneumonias, sexually transmitted diseases (STDs), and skin and soft tissue
infections.
The Effects of Antimicrobial Drug Resistance Are Far -Reaching
People infected with drug-resistant organisms are more likely to have longer and more expensive
hospital stays, and may be more likely to die as a result of the infection. When the drug of choice for
treating their infection doesn’t work, they require treatment with second- or third-choice drugs that
may be less effective, more toxic, and more expensive. This means that patients with an antimicrobialresistant infection may suffer more and pay more for treatment.
Trends in Drug Resistance
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Reports of methicillin-resistant Staphylococcus aureus (MRSA)—a potentially dangerous type
of staph bacteria that is resistant to certain antibiotics and may cause skin and other
infections—in persons with no links to healthcare systems have been observed with increasing
frequency in the United States and elsewhere around the globe.
Multi-drug resistant Klebsiella species and Escherichia coli have been isolated in hospitals
throughout the United States.
Antibiotic-resistant Streptococcus pneumoniae infections have significantly declined, but
remain a concern in some populations.
Antimicrobial resistance is emerging among some fungi, particularly those fungi that cause
infections in transplant patients with weakened immune systems.
Antimicrobial resistance has also been noted with some of the drugs used to treat human
immunodeficiency virus (HIV) infections and influenza.
The development of antimicrobial resistance to the drugs used to treat malaria infections has
been a continuing problem in many parts of the world for decades. Antimicrobial resistance
has developed to a variety of other parasites that cause infection.
Causes of Antimicrobial Resistance
Microbes, such as bacteria, viruses, fungi, and parasites, are living organisms that evolve over time.
Their primary function is to reproduce, thrive, and spread quickly and efficiently. Therefore, microbes
adapt to their environments and change in ways that ensure their survival. If something stops their
ability to grow, such as an antimicrobial, genetic changes can occur that enable the microbe to survive.
There are several ways this happens.
Natural (Biological) Causes
Selective Pressure
In the presence of an antimicrobial, microbes are
either killed or, if they carry resistance genes,
survive. These survivors will replicate, and their
progeny will quickly become the dominant type
throughout the microbial population.
Gene Transfer
Mutation
Most microbes reproduce by dividing every few hours,
allowing them to evolve rapidly and adapt quickly to
new environmental conditions. During replication,
mutations arise and some of these mutations may help
an individual microbe survive exposure to an
antimicrobial.
Microbes also may get genes from each
other, including genes that make the
microbe drug resistant. These genes
are typically found on rings of DNA,
called plasmids. A bacterium that has
acquired an antibiotic resistance gene
on a plasmid may transfer this plasmid
to other bacteria, conferring the
antibiotic resistance trait to them.
Societal Pressures
The use of antimicrobials, even when used appropriately,
creates a selective pressure for resistant organisms.
However, there are additional societal pressures that act
to accelerate the increase of antimicrobial resistance.
Inappropriate Use
Selection of resistant microorganisms is exacerbated by
inappropriate use of antimicrobials. Sometimes
healthcare providers will prescribe antimicrobials
inappropriately, wishing to placate an insistent patient
who has a viral infection or an as-yet undiagnosed
condition.
Hospital Use
Critically ill patients are more susceptible to infections
and, thus, often require the aid of antimicrobials.
However, the heavier use of antimicrobials in these
patients can worsen the problem by selecting for
antimicrobial-resistant microorganisms. The extensive
use of antimicrobials and close contact among sick
patients creates a fertile environment for the spread of
antimicrobial-resistant germs.
Agricultural Use
Scientists also believe that the practice of adding
antibiotics to agricultural feed for livestock promotes drug
resistance. More than half of the antibiotics produced in
the United States are used for agricultural purposes.