Cambridge International A Level Biology Revision Guide

Cambridge International AS Level Biology
216
dangerous infections after surgery, which were mostly
controlled by vancomycin – an antibiotic often used as a
last resort for treating infections when everything else has
failed, so as to lessen the chances of the development of
more such resistant organisms. Then, another bacterium
common in hospitals, Enterococcus faecalis, developed
resistance to vancomycin and this resistance passed to
S. aureus.
Recently, antibiotics called carbapens have been
the antibiotics of last resort for use on bacteria with
multiple resistance. In 2009, carbapen-resistant Klebsiella
pneumoniae was found in Greece. By 2010 it was also
found in Cyprus, Hungary and Italy, and in Greece the
proportion of infections of K. pneumoniae that were
carbapen-resistant had risen to over 25%. In 2010, Greece
used more antibiotics per head of population than any
other European country.
QUESTIONS
10.17 a Describe the ways in which bacteria can protect
themselves against the effects of antibiotics.
b Explain how antibiotic resistance may arise in a
bacterial population.
c Distinguish between vertical and horizontal
transmission in bacteria.
10.18 Suggest why an organism resistant to many
antibiotics has evolved in hospitals and is common
in prisons.
Fortunately, a bacterium resistant to a particular
antibiotic may not be resistant to that antibiotic with a
slightly altered chemical structure. Chemists can make
such semi-synthetic antibiotics to extend the range
available. However, many experts believe that we will
not be able to keep up and that soon there will be no
antibiotics left to treat diseases. This is fast becoming the
case with gonorrhoea, a sexually transmitted infection.
Clearly we should try to reduce the number of
circumstances in which bacteria develop resistance to
antibiotics. Some of the ways in which we can do this
include:
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using antibiotics only when appropriate and necessary;
not prescribing them for viral infections
reducing the number of countries in which antibiotics
are sold without a doctor’s prescription
avoiding the use of so-called wide-spectrum antibiotics
and using instead an antibiotic specific to the infection
(known as narrow spectrum)
making sure that patients complete their course of
medication
making sure that patients do not keep unused
antibiotics for self-medication in the future
changing the type of antibiotics prescribed for certain
diseases so that the same antibiotic is not always
prescribed for the same disease
avoiding using antibiotics in farming to prevent, rather
than cure, infections.
Choosing effective antibiotics
Antibiotics should be chosen carefully. Testing antibiotics
against the strain of the bacterium isolated from people
ensures that the most effective antibiotic can be used in
treatment.
As fast as we develop new antibiotics, bacteria seem
to develop resistance to them. It follows from this that
there is a constant search for new antibiotics, especially
ones that work in a completely different way from those
currently in use.
QUESTION
10.19 Suggest how each of the following might decrease
the chances of an antibiotic-resistant strain of
bacteria developing:
a limiting the use of antibiotics to cases where
there is a real need
b regularly changing the type of antibiotic that is
prescribed for a particular disease
c using two or more antibiotics together to treat a
bacterial infection.