Download What are antibiotics for?

SNC4M
Pathogens and Disease Unit
An introduction to disinfectants, antiseptics and antibiotics
Disinfectants and antiseptics do the same thing – they kill bacteria very rapidly on contact. A
distinction between the two types of agent is made because disinfectants generally kill bacteria on
surfaces, floors and non-living objects whereas antiseptics are used to kill bacteria on the skin of
people or animals. Neither should be confused with antibiotics, drugs that are given to people or
animals to kill bacteria inside the body.
Disinfectants
A wide range of different substances are used as disinfectants, including alcohols (also used as
antiseptics), aldehydes, such as ortho-phthalaldehyde, bleaches based on chlorine compounds,
hydrogen peroxide and also iodine (also another traditional antiseptic) and potassium permanganate
solution. Phenolic compounds also have anti-bacterial activity and are often used in disinfectants
bought for use in the home, and in disinfectant hand-washes and soaps.
Different disinfectants work in different ways. Hydrogen peroxide, which reacts to produce free
oxygen radicals and bleaches that are based on chlorine compounds are very powerful oxidising
agents. They oxidise the complex molecules present on the surface of bacteria, causing their cell
walls and cell membranes to disrupt. The proteins on the surface become irreversibly damaged and
start to stick together forming clumps. This happens very quickly – a strong solution of sodium
hypochlorite solution that is used to disinfect a toilet, for example, kills bacteria within seconds. The
bacterial cell cannot respond to the damage quickly enough and the whole cell simply splits open and
dies.
Recent research has shown that bacteria do have some capacity to resist an attack by bleach. Contact
with hypochlorous acid was found to switch on a gene in some bacteria that is part of the pathway
that bugs use to cope with heat stress and bleach-like substances that cells of the immune system
produce to fight off infection. If the concentration of bleach solution is low, bacteria with genes that
resist this sort of cellular attack might be able to survive cleaning.
Antiseptics
Antiseptics are placed on the skin, usually in an area where the skin has been damaged, such as a cut
or a graze. They are also used to clean the skin before intentional cuts are made in surgical
operations. Those that kill bacteria outright are described as bactericidal. Other antiseptics,
described as bacteriostatic, stop bacteria from growing or dividing, but do not kill them.
Common antiseptics used during the last 150 years or so include alcohol, boric acid, hydrogen
peroxide, iodine, carbolic acid and other phenol compounds, chlorohexadine, sodium chloride, sodium
hypochlorite and calcium hypochlorite. The latter is also known as chlorinated lime and was used by
Ignaz Semmelweis in the 1840s when he tried to prevent puerperal fever spreading in a maternity
ward in Vienna.
SNC4M
Pathogens and Disease Unit
The widespread use of antiseptics did not really begin until the 1870s, due mainly to the work and
publications of the English surgeon Joseph Lister. The link between bacteria and disease was made
around that time and Lister pioneered the use of antiseptics before, during and after surgery, which
was also a new technique at the time.
Modern Use
Disinfectants and antiseptics are now used extensively in hospitals and other medical treatment
centres, where they help to maintain a clean environment that can prevent the spread of bacteria
from person to person. Disinfectants and antiseptics used properly are still able to kill bacterial
strains that have become resistant to antibiotic treatment.
In the last 20 years, the use of disinfectants such as anti-bacterial sprays has increased in the home
but this may not necessarily be a good thing. The vast majority of bacteria in our home environment
are friendly bacteria and do not cause disease. Using anti-bacterial products all over the home is
probably unnecessary. Cleaning danger areas such as toilets, drains and rubbish bins with a suitable
disinfectant or bleach solution is very likely to be sufficient.
Antibiotics Introduction
The word antibiotic comes from the Greek anti meaning 'against' and bios meaning 'life' (a bacterium
is a life form).' Antibiotics are also known as antibacterials, and they are drugs used to treat
infections caused by bacteria. Bacteria are tiny organisms that can sometimes cause illness to humans
and animals. The singular word for bacteria is bacterium.
Such illnesses as tuberculosis, salmonella, syphilis and some forms of meningitis are caused by
bacteria. Some bacteria are not harmful, while others are good for us.
Before bacteria can multiply and cause symptoms our immune system can usually destroy them. We
have special white blood cells that attack harmful bacteria. Even if symptoms do occur, our immune
system can usually cope and fight off the infection. There are occasions, however, when it is all too
much and our bodies need some help - from antibiotics.
The first antibiotic was penicillin. Such penicillin-related antibiotics as ampicillin, amoxicillin and
benzylpenicilllin are widely used today to treat a variety of infections - these antibiotics have been
around for a long time. There are several different types of modern antibiotics and they are only
available with a doctor's prescription in industrialized countries.
SNC4M
Pathogens and Disease Unit
How do antibiotics work?
Although there are a number of different types of antibiotic they all work in one of two ways:
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A bactericidal antibiotic kills the bacteria. Penicillin is a bactericidal. A bactericidal usually
either interferes with the formation of the bacterium's cell wall or its cell contents.
A bacteriostatic stops bacteria from multiplying.
What are antibiotics for?
An antibiotic is given for the treatment of an infection caused by bacteria. Antibiotics target
microorganisms such as bacteria, fungi and parasites. However, they are not effective against viruses
because viruses are not microorganisms. If you have an infection it is important to know whether it is
caused by bacteria or a virus. Most upper respiratory tract infections, such as the common cold and
sore throats are generally caused by viruses - antibiotics do not work against these viruses.
If antibiotics are overused or used incorrectly there is a chance that the bacteria will become
resistant - the antibiotic becomes less effective against that type of bacterium.
A broad-spectrum antibiotic can be used to treat a wide range of infections. A narrow-spectrum
antibiotic is only effective against a few types of bacteria. There are antibiotics that attack aerobic
bacteria, while others work against anaerobic bacteria. Aerobic bacteria need oxygen, while anaerobic
bacteria don't. Antibiotics are among the most frequently prescribed medications in modern medicine.
Antibiotics cure disease by killing or injuring bacteria. The first antibiotic was penicillin, discovered
accidentally from a mold culture. Today, over 100 different antibiotics are available to doctors to
cure minor discomforts as well as life-threatening infections.
Although antibiotics are useful in a wide variety of infections, it is important to realize that
antibiotics only treat bacterial infections. Antibiotics are useless against viral infections (for
example, the common cold) and fungal infections (such as ringworm). Your doctor can best determine
if an antibiotic is right for your condition.