MICROBIOLOGY

Since the beginning people live in a microbial biosphere composed of innumerable micro-organisms of
different types, variants, strains and species.

Organisms that are not harmful are called non-pathogenic organisms and are normally present in or
on certain parts of the body: nose, mouth, skin, intestines etc. The persistent findings of
micro-organisms are also in blood.

On the other hand in a human body there are also usually sterile areas as larynx, trachea, bronchi
and alveoli, where the various defence mechanisms of these organs remove occasional micro-organisms
quickly and efficiently. But these areas may be heavily colonized as well, if diseased. Organisms
that can cause the disease are called pathogens or infectious agents and include bacteria, viruses,
fungi, protozoa and parasitic worms. Bacteria (e.g. cocci, bacilli) are living small organisms
which can be seen only under a microscope and require specific conditions for growth, otherwise
they do not reproduce or they die. They are cultivated on special culture media that can enhance
their growth. Most bacteria do not cause disease, and if they do, they can be damaged by
antibiotics. Some bacteria protect themselves by a covering called a spore. The spore can resist
many antiseptic procedures, such as disinfection, drying and even boiling. For instance, tetanus is
caused by spore-forming organisms. Spores are present in the dirt, in the dust of a room, and are
not destroyed by ordinary laundering, so they can be transferred even by clean sheets and towels.
Viruses cannot be seen under an ordinary microscope, they are injected to a laboratory animal to
develop certain symptoms. They survive only in living tissues so they can be transmitted by direct
contacts (touching, secretion from mouth, nose or urine, sexual contact etc.). There are many
varieties or strains of viruses and their intracellular location within the host. This has made
effective therapy and control more difficult. Examples of viral disease are the common cold,
influenza, measles, mumps, or AIDS. Fungi are multicellular organisms that cause a disease called
mycosis. Thrush, ringworm and histoplasmosis are examples of mycotic diseases. Protozoa are
single-celled organisms that belong to the animal kingdom and can cause such diseases as malaria or
amoebic dysentery and some others.

The most common parasitic worms which can cause an infection are the roundworm, pinworm and
tapeworm. The clinical microbiologist has been charged with the responsibility to the clinician and
to the patient of identifying micro-organisms in a clinical specimen as quickly and accurately as
possible and making a decision which of the micro-organisms isolated from the clinical specimen are
involved in the disease.

The invasion, establishment and growth of a specific pathogenic organism in the tissues are defined
as the infection. It leads to the process called the inflammation. Fever (of a raised body
temperature) is the most common manifestation of the inflammatory response and a signal response in
an infectious disease.

The infectious diseases are those caused by such micro-organisms and capable of being transmitted
to another person by direct or indirect contact. Infection results, if the body’s defence barriers
do not prevent pathogens from entering the body, especially when the immune system is broken.
Infection may be classified in various ways:

1. A local infection is when the pathogens are confined to one area.

2. A general infection is one in which pathogens are spread throughout the body (for example
through blood).

3. An acute infection is manifested by severe symptoms usually connected with high fever.

4. A chronic infection is one that has less severe symptoms and usually lasts over a period of
weeks or months.

Besides, the infection may occur as the secondary one - if it is caused by a different organism
than the one causing the primary infection, for example pneumonia may be a complication of
influenza which was the primary infection but not treated properly.

If the body’s system is in order, it produces substances called antibodies, which are in the blood
and attack things foreign to the body such as micro-organisms. The substances which force the body
to make antibodies are known as antigens (proteins). When the body meets an infective organism, it
produces antibodies against it which protect the person, so that the next time he/she comes across
the same organism, he/she will not be infected by it. The immune system prevents the person from
getting infection.

There are two types of immunisation: active and passive.

Passive immunisation means that a person is injected with antibodies against a disease that are
taken from someone else. It gives immediate protection.

Active immunisation is also called vaccination. It involves injecting a parson with harmless
substances that stimulate the body to produce antibodies against harmful organisms. It takes longer
to work than passive Immunisation but its effects last much longer, too.

There are three types of vaccination:

1. You can use a weakened form of the infective agent, such as with measles and tuberculosis,

2. You can use killed organisms, this is what is done with influenza

3. This type is for bacteria that cause harm by producing poisons. A person is injected by a
weakened form of the poison, such as with tetanus.

Various disorders of the immune system are now very common, especially in children, e.g. allergies.
They are caused by the immune system’s over-reacting to the presence of some type of foreign
substance (e.g. hypersensitivity to the pollen, house dust, some food, drugs or bacteria).

The most typical allergic diseases are:

1.       Erythema - a rash and redness of the skin which is an allergic reaction to some food of
drugs.

2.       Rhinitis - also called hay fever, which is an inflammation of nasal mucus and causes
redness of the eyelid and ’’watery eyes”.

3.       Anaphylaxis - which is a serious allergic reaction that can reach a critical state in some
minutes. It can be a reaction to drugs (penicillin), Insect bites, or vaccines.