The document discusses how bacteria can cause disease in humans by entering a host, reproducing within the host, and damaging host tissues. It then provides details on the various ways bacteria can be transmitted between hosts, including through droplets, contaminated food/water, and vectors. The document also examines how bacteria reproduce rapidly in favorable conditions and calculates the potential growth within a school day. Finally, it discusses several pathogenic protozoa like Entamoeba histolytica and Giardia lamblia that can be transmitted through contaminated water and cause diseases like dysentery.

1. Learning Goals:
To understand the means by which bacterial disease
spreads.
To a understand variety of diseases caused by bacteria.
To examine a variety of protists.

2. 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.

3. 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 so.

4. 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: Work out how many bacteria could be
made in a school day.

5. Bacteria effects on tissues
Flesh eating bacteria
Tumours caused by exotoxins
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 they grow.
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.

6. 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).
Bacterial endotoxins can lead to diabetes
Meningococcemia uses up the bodies clotting
factor resulting in mass haemorrhaging
Endotoxins resist the body’s defence system
better than exotoxins.

7. Treatment of bacterial diseases
• Chemotherapy is the term used when a disease is treated
with chemicals.
• 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
antibiotics.
• Some drugs are narrow-spectrum and act against a limited
variety or microorganisms.
• Other drugs are broad-spectrum and act against many
different kinds of pathogens.

8. • 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.

9. 2. Protoctista
• Protoctistans/protozoans are unicellular
eukaryotic organisms.
• Most species are harmless.
• Many species are very useful and live in close
association with other organisms in a
mutualistic relationship.
• They range in length from 0.1 to 2mm and vary
greatly in shape.

10. Examples of pathogenic protozoa include:
a. Entamoeba histolytica
• This affects ±50 million people worldwide.
• It is found in drinking water.
• In the colon the organisms actually bore
their way into the bowel wall, and cause
ulcerations, severe bloody diarrhoea called
dysentery, and abdominal pain.
• Some of the amoeba can inter the blood
stream where they can spread to other
tissues, such as the liver, lungs and brain.

11. b. Trichomonas vaginalis
This is a single cell flagellum
parasite that lives in the female
vagina and the male urethra.
This STD is often asymptomatic but usually
causes vaginitis or urethritis.
It can live for up to 24 hours outside of a host
in water, semen or urine.

12. c. Trypanosoma gambiense
More than 66 million people in 36
countries of sub-Saharan Africa suffer
from human African trypanosomiasis (HAT).
There are two forms of African sleeping
sickness, caused by two different sub-species.
Both are transmitted to humans through the
bite of a tsetse fly.
When untreated, HAT ultimately ends in death.

13. d. Giardia lamblia
This is found in contaminated water supplies.
Contamination occurs from human faeces, poor
hygiene or water-borne transmission.
It causes low-grade intestinal problems in
humans, and is difficult to eliminate from the
body.