This article gives a brief overview of the different types of microbes
that can cause infections, and a brief overview of the use of
antibiotics.
What are microbes?
Doctors classify microbes
or 'germs' into different groups. Four common groups of microbes that
cause illness are described below.
Bacteria
There are many different types of
bacteria. Some are helpful and protective to humans. Some flourish
naturally in our bodies - particularly in the bowel and vagina - and
help to protect the body. However, infection with some bacteria can
cause serious illnesses such as meningitis, pneumonia, tuberculosis,
etc. A bacterial infection may be treated with a course of antibiotics.
Viruses
These are smaller and different to
bacteria. Many different types exist. Most of the common 'minor'
illnesses are caused by viruses. For example, colds, coughs, 'flu, sore
throats, chicken pox, and some other rashes. It is a standing joke that
doctors often diagnose 'a virus', but in fact most common infections
are due to a viral infection.
For many viral infections there
are no effective anti-viral drugs (unlike antibiotics for bacteria).
Fortunately, the immune system in the body usually fights off most
viral infections within a few days. Taking 'symptomatic' treatments for
fever or catarrh such as paracetamol is all that needs to be done.
However,
some viruses are not fought off and can be very serious. The HIV virus
is a good example. There are some anti-viral drugs that are used for
certain infections - such as antiretroviral drugs used to treat HIV.
Another example is aciclovir and related drugs which are used to treat
certain herpes virus infections. As a rule, anti-viral drugs do not
clear the virus from the body. They usually work by stopping the virus
from multiplying and so 'control' the virus and the infection that it
causes.
Fungi
Many types of fungi exist and cause
problems in humans, animals and plants. Fungal infections commonly
affect the skin and nails in humans. They cause ringworm, athlete's
foot, other localised skin rashes, and infections in and around nails.
Modern creams usually work well to clear a local fungal rash quickly.
However, nail infections can be rather stubborn and may need long term
treatment of anti-fungal medicines taken by mouth.
Yeasts
The most common yeast infection is
thrush. This is due to a yeast called Candida which thrives in moist
airless, warm areas of the body. It causes infections in the vagina,
some cases of nappy rash in babies, and sometimes infects other areas
of the body. Treatment usually works well with anti-yeast creams and
medicines.
Antibiotics
Antibiotics are no 'cure all'
for infections. Antibiotics will only clear infections caused by
bacteria. They do not work when an infection is caused by viruses,
fungi or yeasts. As mentioned, most common infections are caused by
viruses when an antibiotic will not be of use. Even if you have a
bacterial infection, the immune system can clear most bacterial
infections. For example, antibiotics usually do little to speed up
recovery of bronchitis, or most ear, nose, and throat infections that
are caused by bacteria.
However, you do need antibiotics if
you have certain serious infections caused by bacteria such as
meningitis or pneumonia. In these situations, antibiotics are often
life-saving. When you are ill, doctors are skilled at checking you over
to rule out serious illness, and to advise if an antibiotic is needed.
How do antibiotics work?
Some work by
killing the bacteria. This is often done by interfering with the
structure of the cell wall of the bacteria. Some work by stopping the
bacteria from multiplying.
Some possible problems with antibiotics
Antibiotics
are not without problems. This is why it is not usually good practice
to take antibiotics 'just in case' an infection is bacterial, but to
only take them when they are really needed. For example:
- Antibiotics can cause side effects such as allergies,
diarrhoea, rashes and nausea. Side effects are quite common. Most side
effects are not serious, but some people have died from a severe
allergic reaction to an antibiotic.
- Antibiotics can kill off normal 'defence' bacteria which live in the bowel and vagina. This may then allow thrush to develop.
- Overuse of antibiotics has led to some bacteria mutating and
becoming resistant to some antibiotics which may then not work when
really needed. For example, MRSA is a bacterium that has become
resistant to many different antibiotics and is difficult to treat.
- Some antibiotics may interact with other medicines that you might
take. This may cause reactions, or reduce the effectiveness of one or
other of the treatments. One well known example is that certain
antibiotics can reduce the effectiveness of 'the pill' (the oral
contraceptive pill). So, when you are prescribed an antibiotic you
should tell a doctor if you are on 'the pill' or if you take other
medicines.
- Food and drink affect the absorption of some antibiotics - so follow the instructions on how to take a course of antibiotics.
In summary
Doctors are skilled in
diagnosing which conditions are in need of antibiotics. So do not be
surprised if a doctor does not recommend an antibiotic for conditions
caused by viruses or non-bacterial infections, or even for a mild
bacterial infection.
Occasionally, a virus infection or minor
bacterial infection develops into a more serious 'secondary' bacterial
infection. See a doctor to review the situation if an illness appears
to change, becomes worse, does not go after a few days, or if you are
worried about any new symptom that develops.
References
© EMIS and PiP 2008 Updated: 22 Jan 2008
