To be able to differentiate between different
types of diseases.
To understand important aspects of bacteria.
To be able to classify bacteria based on shape.
Causes of disease can be grouped into 2 main
1. Congenital diseases: inherited and passed down
from parent to offspring.
Verne Troyer has Achondroplasia
2. Acquired diseases –contracted at some stage
over a lifetime
- can be subdivided into 2 types:
a. Lifestyle diseases - caused by an unhealthy
lifestyle e.g. heart disease; type 2 diabetes.
b. Infectious disease – disease caused by a
• One of the main causes of disease in an
organism is the presence of another organism
in or on it. Such an invading organism is called
• The organism that they ‘feed’ on is called the
• If a parasite causes a disease state (i.e. if it
makes the host sick in any way) it is said to be
• Pathology is the branch of science involved in
the study of disease and diseased tissue.
Pathogens may be a microorganism such as
bacteria, viruses, fungi or prion; or may be a
multicellular organism such as worms.
Most pathogens, and their associated
infectious disease, can be transmitted from
person to person (i.e. are contagious).
Many infectious diseases result in death.
Classification of diseases
• Traumatic illnesses are injuries,
• Inflammatory diseases cause fever and
Hand with gout
• Neoplastic conditions involve tumours or
• Malignant cancers are those that spread
active cancer cells throughout the body,
Tumour on the palate
• Benign cancers are those where cancer cells form
tumours at one site.
• Acute relates to a short, sudden episode of
• Chronic relates to a continuing occurrence of the
Infectious diseases - Pathogens
Bacteria are unicellular, prokaryotic organisms.
Bacteria are found everywhere and only a few
Most bacteria are saprophytes – they obtain their
nutrients from dead and decaying organisms.
In humans, bacteria live in the intestine and help
break down food.
Bacteria sample from the human tongue
• Bacteria vary greatly in size and morphology (shape).
• Bacteria are generally between 1/1000 and 1/20 of a mm in length.
(baccilus, spirochaete, coccus,
Baccilus Anthrax is
the bacteria involved
in the infection
commonly known as
anthrax. It affects
the function of the
lungs, the digestive
system and the skin of
Borellia bergdorferi is
a spirochete bacteria
responsible for Lyme
disease. Although the
first symptom of a
rash seems minor, the
disease can result in
damage to the heart,
nerves, brain, and
Ticks are the vector
of spread for this
Escherichia coli is a
baccilis normally found
in the intestines of
mammals. Some strains
are responsible for
causing food poisoning,
and the reason for
mass recall of some
is a coccus bacteria
inflammation of the
of the brain.
Yersinia pestis is a
bacteria which was
responsible for Black
Death which was
responsible for loss of
at least 1/3rd of the
population of Europe
between 1347 and
Classifying bacteria on oxygen requirement
• Bacteria that need oxygen for their survival are called
• Bacteria that do not require oxygen for survival are
called anaerobic bacteria.
• Facultative anaerobes can survive wether in oxygen
• Obligate anaerobes grow and reproduce only in the
absence of oxygen.
Examples and the
disease they cause
Grow in presence of
– external ear infection
Grow wether oxygen is
present or not
Streptococcus pyogenes –
Grow only in absence of
Clostridium botulinum –
C. tetani – tetanus
C. perfringens - gangrene
Gram Positive and Gram Negative bacteria:
• Bacteria are grouped as ‘Gram Positive’ bacteria and ‘Gram
Negative’ bacteria, which is based on the results of Gram
Staining Method, in which an agent is used to bind to the cell
wall of the bacteria.
Gram-positive bacteria take up the violet colour of the stain,
Gram-negative bacteria stain pink.
• Some bacteria have a special polysaccharide called teichoic
acid in their cell walls, and are susceptible to penicillin and
The chemical components of the cell wall of Grampositive and gram-negative bacterium
• The outer layer of lipid compounds in gram-negative bacteria
enables the bacteria to resist drugs.
• It also makes phagocytosis of the bacteria very difficult.
• Other drugs are effective against these types of bacteria.
Classification based on nutritional patterns
This is one of the most important classification types as it takes
into account the most important aspect of bacteria growth and
• Some bacteria are photosynthetic (autotrophs) use light as
their energy source.
• Only some of these bacteria are able to use CO2 as their carbon
• Chemosynthetic organisms obtain their energy from oxidation
• Some of these can only oxidise organic compounds for their
carbon source. Others can oxidise inorganic substances such
as ammonia, sulfides and iron compounds. Other
heterotrophic bacteria obtain carbon and/or sugar from the
the living cells or organism they are in).
copy fig 7.8 p.193
Classification based on Phyla:
• Based on the morphology, DNA sequencing,
conditions required and biochemistry, scientists have
classified bacteria into phyla.
• Each phylum further corresponds to number of
species and genera of bacteria.
• The bacteria classification includes classification
based on the habitat of the bacteria.
How do bacteria cause disease?
• Bacteria can cause disease in humans if:
1. They can enter a person who acts as a host
2. They can reproduce in the host
3. They act adversely on the tissue of the host.
Task: List several ways in which bacteria can be
transmitted to a person.
Transmission to a host
• Transmission of bacteria (and other pathogens) occurs by:
a) From one person to another through droplets if an infected
person coughs, sneezes or comes into body contact
b) Contaminated water and food
c) Carried from one host to another by a vector (an animal
host such as a mosquito, rat or fly)
A carrier of a disease is someone who has the disease, be
shows no symptoms, so passes it on to others unaware of doing
Reproduction of bacteria
• In order to reproduce, bacteria need an environment
with adequate nutrients and water, and an
appropriate temperature and pH.
• When conditions are favourable, bacteria reproduce
very quickly, about every 20 minutes or so.
Task: Q2 p.220
Bacteria effects on tissues
Bacteria can damage the host in several ways:
1. By producing enzymes that break down or digest tissues.
2. By producing poisonous toxins.
a) Exotoxins are released into the surroundings by bacteria as
Exotoxins are some of the most lethal substances
known, and can (i) inhibit protein synthesis;
(ii) Damage cell membranes or disrupt transport of materials
across cell membranes; or
(iii) Interfere with normal nerve function.
Toxins retains their destructive powers after the bacteria dies.
b) Endotoxins are derived from the lipopolysaccharide
layer in the cell wall of Gram-negative bacteria and are
released after the cell lyses (breaks open).
Endotoxins resist the body’s defence system better
Task: copy table 7.2 p.198
Treatment of bacterial diseases
• Chemotherapy is the term used when a disease is treated with
• Many chemicals are produced, or have been extracted from bacteria
and fungi to fight disease-causing agents.
• Naturally occurring compounds which kill bacteria are called
• Some drugs are narrow-spectrum and act against a limited variety or
• Other drugs are broad-spectrum and act against many different
kinds of pathogens.
• Broad-spectrum antibiotics are useful when the doctor is not
sure which bacterium is causing an infection.
• Sensitivity tests are carried out to determine which drug is
most effective against the infecting bacteria.
• A drug should be selectively toxic – it should kill the infecting
cells without destroying the host cells.
• Some drugs have adverse effects (side effects) on a host.
Task: Copy table 7.3 p.200