See also APOPTOSIS; NEUROTRANSMITTER; ORPHAN
DRUG.
antibiotic resistance The adaptation of bacterial
strains to certain of the ANTIBIOTIC MEDICATIONSdoc-
tors prescribe to treat infections the BACTERIA
cause, rendering the antibiotic ineffective. Such
adaptation is an evolutionary mechanism that
allows the strain of bacteria to survive. Though in
most situations the strain of bacteria remains sen-
sitive to other antibiotics even as it develops resist-
ance to a particular antibiotic, antibiotic resistance
is a very serious concern in modern health care
because the more common strains of bacteria are
developing broad bases of resistance to multiple
antibiotics. A few strains have mutated to resist all
available antibiotics, presenting a worrisome chal-
lenge for fighting the infections they cause.
Bacteria, Infection, and AntibioticsBacteria are single-cell microorganisms that exist
in broad families with numerous strains, or varia-
tions, within the same family. Under supportive
circumstances each individual strain can cause
unique and specific infections. Most bacteria that
cause INFECTIONin people are normally present in
the body and the environment. Ordinarily these
bacteria are harmless or even beneficial to body
functions, such as the bacteria in the gastroin-
testinal tract that aid in digestion. NORMAL FLORA
bacteria become pathogenic when there is a
breach, such as a wound, in the body’s protective
mechanisms, or when something goes awry with
the body’s balance of microorganisms and the
IMMUNE SYSTEM cannot keep bacterial growth in
check.
Antibiotics kill bacteria, either by direct toxicity
to the bacteria or by preventing the bacteria from
reproducing. Antibiotics are effective for treating
only bacterial infections; they cannot treat viral
infections. Chronic conditions such as BRONCHITIS
and OTITISmedia (middle EARinfection) are often
viral, yet are among the top ailments for which
doctors prescribe antibiotics. It is not possible to
determine the cause of an infection by evaluating
the symptoms, though certain characteristics
make it more likely that an infection is bacterial.
Only a laboratory culture of cells from the infec-
tion, in which cells of a bacterial strain may or
may not grow in the lab, can identify the cause of
an infection as bacterial.How Bacteria Acquire Resistance
Bacteria reproduce rapidly, which gives them the
opportunity to change rapidly. Over multiple gen-
erations the bacteria’s DNA—its GENETIC CODE—
mutates to establish adaptations beneficial to the
bacterial strain’s survival. These adaptations
include increased resistance to the antibiotics that
people take to fight the infections the strain
causes. Bacteria generally mutate through one of
three processes:- Spontaneous MUTATIONis when changes occur
within the DNA alter the bacteria’s adaptive
ability across the bacterial strain. Resistance
due to spontaneous mutation, also called evo-
lutionary mutation, develops over multiple
generations of the bacterial strain. - Transformation is when the DNA from resistant
bacteria enter another bacteria that are not yet
resistant. Also called DNA uptake, transforma-
tion expedites the mutation process to allow
bacterial strains to become more rapidly resist-
ant than they would through spontaneous
mutation. - Plasmid transfer is when plasmids (molecules
that contain incomplete fragments of genetic
material) move among different kinds of bacte-
ria. Plasmids impart limited genetic encoding
related primarily to the survivability of a bacte-
rial strain and can result in rapid adaptation to
produce antibiotic resistance. Because antibiotic
resistance has become a key purpose of plasmid
transfer, researchers designate such plasmids as
R plasmids.
Resistance resulting from spontaneous, or evo-
lutionary, mutation is the most common adapta-
tion process and accounts for most of the resistant
strains of GONORRHEAand Staphylococcus aureusinfec-
tions. Transformation, or DNA uptake, is a more
sophisticated, biologically intentional process than
spontaneous mutation. Among the three mutation
processes plasmid transfer is the most efficient and
creates the greatest concern in regard to antibiotic
resistance. Plasmids can transfer among different
strains of bacteria within a bacterial family, sharing150 Drugs