Antibiotic Resistance (cont.)
The History of Antimicrobial (Drug) Resistance
Introduction
Microbes are living organisms that reproduce, thrive, and spread
quickly and efficiently increasing their numbers. Microbes include bacteria
(Staphylococcus aureus), viruses (colds and influenza, which causes the "flu"),
fungi (e.g., Candida albicans, which causes some
yeast infections), and
parasites (e.g., Plasmodium falciparum, which causes malaria).
Antimicrobial is a general term given to medicines that kill or slow the
growth of microbes.
Antimicrobial drug resistance is the ability of a microbe to grow in the
presence of a chemical that would normally kill it or limit its growth.
History
In 1928 while working with Staphylococcus bacteria, Scottish scientist
Alexander Fleming noticed that a type of
mold growing by
accident on a laboratory plate was protected from, and even repelled, the
bacteria. The active substance, which Fleming called
penicillin, was literally an antibiotic
- it
killed living organisms.
Thus began the age of using natural and, later, synthetic drugs to treat
people with bacterial infections. Though not widely popular until the 1940s,
antibiotics and other antimicrobials (medicines that kill or slow growth of a
microbe) have saved countless lives and blunted serious complications of many
feared diseases and infections. The success of antimicrobials against
disease-causing microbes is among modern medicine's great achievements.
The Problem
After more than 50 years of widespread use, evolution of disease-causing
microbes has resulted in many antimicrobials losing their effectiveness.
As microbes evolve, they adapt to their environment. If
something stops them from growing and spreading-such as an antimicrobial-they
evolve new mechanisms to resist the antimicrobials by changing their genetic
structure. Changing the genetic structure ensures that the offspring of the resistant microbes are also
resistant.
Antimicrobial resistance makes it harder to eliminate infections from the
body. As a result of a microbe's ability to survive in spite of antimicrobials,
some infectious diseases are now more difficult to treat than they were just a
few decades ago. In fact, antimicrobials have helped people so effectively that
humans are hurting the protective value of medicines through overuse and misuse.
More prudent use of antimicrobials will help to slow the development of
resistance.
Causes of antimicrobial drug 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
environment and change in ways that ensure their survival. If something stops
their ability to spread, such as an antimicrobial, genetic changes can occur
that enable the microbe to survive. There are several ways this happens.
Natural [Biological] Causes
Mutation
Microbes reproduce by dividing every few hours, allowing
them to evolve rapidly and adapt quickly to new environmental conditions. With
each replication, mutations arise, and some of these mutations may help an individual
microbe survive exposure to an antimicrobial.
Picture of Mutation Causes of Drug Resistance
Gene Transfer
Microbes may also acquire genes from each other, including genes that make
the microbe drug resistant.
Picture of Gene Transfer Facilitates Drug Resistance
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.
Societal Pressures
The use of antibiotics, 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 physicians will prescribe inappropriate antimicrobials
wishing to placate an insistent patient who has a viral infection or an as-yet
undiagnosed condition.
Inadequate Diagnostics
More often, physicians must use incomplete or imperfect information to
diagnose an infection and thus prescribe an antimicrobial just-in-case or
prescribe a broad-spectrum antimicrobial when a specific antibiotic might be
better. These situations contribute to selective pressure and accelerate
antimicrobial resistance.
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 promotes drug resistance. More than half of the antibiotics
produced in the United States are used for agricultural purposes. However, there
is still much debate about whether drug-resistant microbes in animals pose a
significant public health burden.
Next: Diagnosis of antimicrobial drug resistance »
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