This document discusses microorganisms that cause disease in humans. It identifies the main types of pathogens as viruses, bacteria, protozoa, and fungi. Viruses hijack host cells to replicate and are usually self-limiting, while bacteria come in various shapes and sizes and antibiotics are often used to treat bacterial infections. Protozoa and fungi can also cause diseases like amoebic dysentery and ringworm, respectively, and are treated with special medicines. The development of drug resistance in pathogens is a growing health concern caused by overuse of antibiotics. Identifying the causative organism is important for effective treatment and preventing resistance.

1. Microbiology Concepts
IHS Unit 3

2. Goals
• Identify and discuss organisms that cause
disease in humans.

3. Pathogens
• An organism that causes disease in humans is
called a pathogen.
– A pathogen that causes a specific disease is the
agent.

4. Types of Pathogens
• Most communicable (infectious) diseases in
humans are caused by either viruses or
bacteria.
• Some diseases are caused by protozoa or
fungi.
• The specific traits of a given organism
determine what type of disease is caused and
how it passes from person to person.

5. Bacteria
• Single celled microorganisms
that are the most numerous
type of organism on the planet.
– Only a small percentage of
bacteria cause disease in
humans. Most are harmless or
even helpful.
– Variations in size, cell wall,
chemicals produced, etc. effect
the types of disease caused.
– Antibiotics are effective in
treating infections that are not
self limiting.

6. Viruses
• Viruses are strange organisms that
are not even truly living.
– They do not look like other life on our
planet, leading to some biologists
calling them “aliens.”
– In order to “live” and replicate
themselves, they hijack other cells and
use there organelles to make viral DNA.
– Then, they kill that cell and release the
new viruses.
– Viruses are usually self limiting, and
can be treated by dealing with
symptoms or antiviral medication.
– Antibiotics are NOT effective.

7. Protozoa
• Literally means
“primitive animal”
– Single celled organisms
that behave sort of like
animals.
– Cause disease such as
amoebic disentery and
malaria.
– Technically a parasite.
– Special antiprotozoal
medicine is used to
treat.

8. Fungi
• These are organisms
such as molds and
yeast.
– Reproduces via spores
(spores are often an
agent of disease.
– Some fungi even help
us by producing
antibiotics.
– Fungi are treated with
antifungal medicines.

9. Resistance
• If an organism is resistant, it means that it
does not respond to the normal treatments
used for it.
– This is dangerous, because it often means that
patients have to take stronger medications with
more side effects or that there is no way to treat
the disease.
– Resistance is caused by both overuse of antibiotics
in healthcare and the use in agriculture.

10. Importance in Healthcare
• Health care providers and Laboratory
specialists have the task of figuring out what
type of organism causes disease.
– This is the only way we can have specific and
effective treatment.
– Choosing the wrong treatment can allow the
disease to get worse, and also contributes to the
growing problem of antibiotic resistant organisms.