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P A R T 2
Chemotherapeutic agents
BACTERIA AND RESISTANCE TO
ANTIBIOTICS
Bacteria have survived for hundreds of years because
they can adapt to their environment. They do this by
altering their cell wall or enzyme systems to become
resistant to (i.e. protect themselves from) unfavourable
conditions or situations. Many species of bacteria have
developed resistance to certain antibiotics. For example,
bacteria that were once very sensitive to penicillin have
developed an enzyme called penicillinase, which effec-
tively inactivates many of the penicillin-type drugs. New
drugs have had to be developed to effectively treat infec-
tions involving these once-controlled bacteria. It is very
important to use these drugs only when the identity and
sensitivity of the offending bacterium have been estab-
lished. Indiscriminate use of these new drugs can lead
to the development of more resistant strains for which
there is no effective antibiotic (see later discussion of
new antibiotics for additional information on linezolid).
The longer an antibiotic has been in use, the greater
is the chance that the bacteria will develop into a resist-
ant strain. Efforts to control the emergence of resistant
strains involve intensive educational programs that
advocate the use of antibiotics only when necessary and
effective and not for the treatment of viral infections
such as the common cold (Box 9.3).
In addition, the use of antibiotics may result in the
development of superinfections or overgrowth of resistant
pathogens, such as bacteria, fungi or yeasts, because
antibiotics (particularly broad-spectrum agents) destroy
bacteria in the flora that normally work to keep these
opportunistic invaders in check. When “normal” bacteria
are destroyed or greatly reduced in number, there is
nothing to prevent the invaders from occupying the host.
In most cases the superinfection is an irritating adverse
effect (e.g. vaginal yeast infection, candidiasis, diarrhoea),
but in some cases, the superinfection can be more severe
than the infection that was originally being treated. Treat-
ment of the superinfection leads to new adverse effects
and the potential for different superinfections. A vicious
cycle of treatment and resistance is the result.
KEY POINTS
■■
The goal of antibiotic therapy is to reduce the
population of invading bacteria to a size that the
human immune response can deal with.
■■
Bacteria can be classified as gram-positive (frequently
found in respiratory infections) or gram-negative
(frequently found in GI and GU infections). They can
also be classified as anaerobic (not needing oxygen)
or aerobic (dependent on oxygen).
■■
Culture and sensitivity testing ensures that the correct
antibiotic is chosen for each infection, a practice
that may help to decrease the number of emerging
resistant-strain bacteria.
KEY POINTS
Using antibiotics properly
In 2003, the US Food and Drug Administration (FDA) and
Centers for Disease Control and Prevention (CDC) joined
efforts to educate the public and healthcare providers
about the dangers of inappropriate use of antibiotics.
The evidence-based practice guidelines combine data
from many studies to outline the most efficacious use
of antibiotics.To review some of the studies, review the
references listed in the Bibliography. Nurses and midwives
should include some of the following points about the
risks and dangers of antibiotic abuse in each person’s
education plan:
• Explain clearly that a particular antibiotic is effective
against only certain bacteria and that a culture needs to
be taken to identify the bacteria.
• Explain that bacteria can develop resistant strains that
will not be affected by antibiotics in the future, so use
of antibiotics now may make them less effective in
situations in which they are really necessary.
• Ensure that people understand the importance of taking
the full course of medication as prescribed, even if they
feel better. Stopping an antibiotic midway through a
regimen often leads to the development of resistant
bacteria. Using all of the medication will also prevent
people saving unused medication to self-treat future
infections or to share with other family members.
• Tell people that allergies may develop with repeated
exposures to certain antibiotics. In addition, explain
to people that saving antibiotics to take later, when
they think they need them again, may lead to earlier
development of an allergy, which will negate important
tests that could identify the bacteria making them sick.
• Offer other medications, such as antihistamines,
decongestants, or even chicken soup, to people who
request antibiotics; this may satisfy their need for
something to take. Explaining that viral infections do not
respond to antibiotics usually offers little consolation to
people who are suffering from a cold or the flu.
The publicity that many emergent, resistant strains of
bacteria have received in recent years may help to get the
message across to people about the need to take the full
course of an antibiotic and to use antibiotics only when
they are appropriate.
The evidence
BOX 9.3
