INTRODUCTION TO MICROBIOLOGY
Dr Nazia Khan
Assistant professor
College of medicine
Majmaah university
LEARNING OBJECTIVES
AFTER STUDYING THIS CHAPTER, YOU SHOULD BE ABLE TO:
A.
Explain fundamentals of microbiology and its medical importance
B.
Give brief history of evolution of microbiology with special
contribution of Robert Koch and Louis Pasteur
C.
Describe branches of microbiology
D.
Describe basic characteristics of bacteria, viruses, parasites and
fungi with examples of common diseases
INTRODUCTION

The Science of Microbiology: Introduction

Microbiology is the study of microorganisms(microbes) ,a large and diverse group of
microscopic organisms that exist as single cells or cell clusters; it also includes
viruses, which are microscopic but not cellular .

They are responsible for cycling the chemical elements essential for life, including
carbon, nitrogen, sulfur, hydrogen, and oxygen; more photosynthesis is carried out
by microorganisms than by green plants .

It has been estimated that 5 x1030 microbial cells exist on earth .

Humans also have an intimate relationship with microorganisms; more than 90% of
the cells in our bodies are microbes

The various categories of microbes include viruses, bacteria, archaea, protozoa,
and certain types of algae and fungi.
1.
TERMINOLOGIES
Mutualism, one that benefits all of
the contributing parties
2.
Symbiosis: a continuing association
of different organisms
3.
Parasitism: If the exchange operates
primarily to the benefit of one party,
the association is described as
parasitism, aGLOBAL
relationship
a WHO 2013
BURDENin
OFwhich
DISEASEShost provides the primary benefit to
the parasite
4.
Disease-causing microorganisms are
technically known as pathogens
(also referred to as infectious
agents)
5.
The vast majority of known microbes
are nonpathogens— microbes that
do not cause disease.
GLOBAL BURDEN OF DISEASES- WHO 2013
WHY STUDY MICROBIOLOGY
1.
We have, living on and in our bodies approximately
10 times as many microbes as the total number of
cells
Collectively, these microbes are known as our
indigenous microflora (or indigenous microbiota)
and, for the most part, they are of benefit to us
2.
Some of the microbes that colonize (inhabit) our
bodies are known as opportunistic pathogens (or
opportunists).
3.
Microbes are essential for life on this planet. For
example, some microbes produce oxygen by the
process known as photosynthesis
4.
Many microbes are involved in the decomposition of
dead organisms and the waste products of living
organisms. Collectively, they are referred to as
decomposers or saprophytes.

By definition, a saprophyte is an organism that lives
on dead or decaying organic matter.

Saprophytes aid in fertilization by returning inorganic
nutrients to the soil.
5.
Algae and bacteria serve as food for tiny animals
6.
Some microbes live in the intestinal tracts of animals,
where they aid in the digestion of food
7. Some bacteria and fungi produce antibiotics that
8. Microbes are essential in the field of genetic engineering. such as insulin,
various types of growth hormones, interferons, and materials for use as
vaccine
9. For many years, microbes have been used as “cell models.”
10. They cause diseases
•
Infectious diseases are leading cause of death in the world and the third
leading cause of death in the United States (after heart disease and
cancer)
PIONEERS IN THE SCIENCEOF MICROBIOLOGY
. Bacteria and protozoa were the first microbes to be

observed by humans. It then took about 200 years before
a connection was established between microbes and
infectious diseases.

Among the most significant events in the early history of
microbiology were
i.
the development of microscopes,
ii.
bacterial staining procedures,
iii.
Techniques that enabled microorganisms to be cultured
(grown) in the laboratory, and steps that could be taken
to prove that specific microbes were responsible for
causing specific infectious diseases.
During the past 400 years, many individuals contributed to
our present understanding of microbes.
Anton van Leeuwenhoek (1632–1723)
•Anton van Leeuwenhoek was the first
person to see live bacteria and
protozoa,
•“Father of Microbiology,” the “Father
of Bacteriology,” and the “Father of
Protozoology”.
•Leeuwenhoek was not a trained
scientist.he was a fabric merchant, a
surveyor, a wine assayer, and a minor
city official in Holland.
•As a hobby, he ground tiny glass lenses,
which he mounted in small metal
frames, thus creating what today are
known as single-lens microscopes or
simple microscopes.
• During his lifetime, he made more
than 500 of these microscopes
Louis Pasteur (1822–1895)
•French chemist,
•Below are some of his most significant
contributions:
1. While attempting to discover why wine
becomes contaminated with undesirable
substances, Pasteur discovered what occurs
during alcoholic fermentation
2. The theory of spontaneous generation.
3. He discovered forms of life that could exist
in the absence of oxygen. He introduced
the terms “aerobes”(organisms that require
oxygen) and “anaerobes” (organisms that
do not require oxygen).
4. He developed the process called
Pasteurization to kill microbes
Contn……
5.
He discovered the infectious agents that caused the
silkworm diseases that were crippling the silk industry in
France. He also discovered how to prevent such diseases.
6.
Pasteur made significant contributions to the germ
theory of disease—the theory that specific microbes
cause specific infectious diseases.
7.
Pasteur championed changes in hospital practices to
minimize the spread of disease by pathogens.
8.
Pasteur developed vaccines to prevent chicken cholera,
anthrax, and swine erysipelas (a skin disease).
9.
Pasteur developed a vaccine to prevent rabies in dogs
and successfully used the vaccine to treat human rabies.
ROBERT KOCH(1843–1910)

German physician
1.
He made many significant contributions to the germ
theory of disease. For example, he proved that the
anthrax bacillus (B. anthracis), was truly the cause of
anthrax. He developed Koch’s Postulates
2.
Koch discovered that B. anthracis produces spores,
capable of resisting adverse conditions.
3.
Koch developed methods of fixing, staining, and
photographing bacteria.
4.
Koch developed methods of cultivating bacteria on
solid media. He obtained pure cultures of bacteria.
He discovered the bacterium (M. tuberculosis) that
causes tuberculosis and the bacterium (Vibrio
cholerae) that causes cholera.
5.
Koch’s work on tuberculin (a protein derived from
M. tuberculosis) ultimately led to the development
of a skin test valuable in diagnosing tuberculosis
1.
The microorganism or other
pathogen must be present in all
cases of the disease
2.
The pathogen can be isolated
from the diseased host
and grown in pure culture
3.
The pathogen from the pure
culture must cause the disease
when inoculated into a healthy,
susceptible laboratory animal
4.
The pathogen must be reisolated from the new host
and shown to be the same as the
originally inoculated pathogen
Exceptions to Koch’s Postulates
Examples of circumstances in which Koch’s Postulates cannot
be fulfilled :
A.
Certain pathogens will not grow on artificial media. Ex:
viruses, rickettsias, chlamydias and the bacteria that
cause leprosy and syphilis.
Microbes having complex and demanding nutritional
requirements are said to be fastidious (meaning fussy).
Although certain fastidious organisms can be grown in the
laboratory others cannot be grown in the laboratory
B.
It is necessary to infect laboratory animals with the
pathogen being studied
many pathogens are species-specific, meaning that they infect
only one species of animal. For example, some pathogens that
infect humans will only infect humans. Thus, it is not always
possible to find a laboratory animal that can be infected with
C.
Some diseases, called synergistic infections, are caused
not by one particular microbe, but by the combined effects
of two or more different microbes. It is very difficult to
reproduce such synergistic infections in the laboratory.
D.
certain pathogens become altered when grown in vitro.
Some become less pathogenic, whereas others become
nonpathogenic. Thus, they will no longer infect animals
after being cultured on artificial media.
E.
not all diseases are caused by microbes
Branches of microbiology

Bacteriology: The study of bacteria

Mycology: The study of fungi

Protozoology: The study of protozoa

Parasitology: The study of parasites

Immunology: The study of the immune system

Virology: The study of viruses

Nematology: The study of the nematodes
GEN CHARACTERISTICS-BACTERIA

Small- Need simple microscope

Prokaryotic

No specific nucleus

One chromosome only

DNA and RNA

No membrane bound organelle

70S ribosome

Replicate by binary fission

Cell membrane without sterol (except
Mycoplasma)

Cell wall-Peptidoglycans

e.g. E.coli, Staph aureus
GEN CHARACTERISTICS-VIRUSES

Very Minute- Need electron
microscope

Acellular

No nucleus

Either DNA or RNA

Replicates in host cells only

No ribosome

No functional cell membrane

No cell wall

e.g. Human immuno-deficiency
virus, Varicella zoster virus
GEN CHARACTERISTICS-FUNGI

Small

Eukaryote

Proper nucleus, nuclear memb

More than 1 chromosome

Mitochondria & other cell bound
organelle

80S ribosome

Cell membrane Ergosterol

Complex carbohydrate cell wall
–Chitin, Mannan, Glucans

e.g. Candida albicans,
Aspergillus
PROPERTIES OF MICROORGANISMS
Features
Viruses
Bacteria
Fungi
Parasites
Size
0.02-0.3 µ
0.3-2µ
3-10µ
15-25µ#
Cell Type
Acellular
Prokaryote
Eukaryote
Eukaryote
DNA/ RNA
Either
Both
Both
Both
Nucleic acid
replication
Host cell
Continuous
G & S phase
G & S phase
Replication
Complex
Binary fission
Mitosis/
Meiosis
Mitosis/
Meiosis
Organelle
Uses host
Not membrane
bound
Membrane
bound
Membrane
bound
Ribosomes
None
70S(30S+50S)
80S(40S+60S)
80S(40S+60S)
Cell memb
Env/Non
env
No sterol
#Mycoplasma
Ergosterol
Cholesterol
Cell wall
None
Peptidoglycan
Chitin,
Glucan
None
Self assessment

Which of the following bacteria was not discovered by Robert Koch?
a)
Bacillus anthracis
b)
Mycobacterium tuberculosis
c)
Salmonella typhi
d)
Vibrio cholera

The primary use of Koch's postulates is to
a)
Clearly identify and characterize a particular organism
b)
Isolate organism from diseased individual
c)
Demonstrate that the disease is caused by a microorganism
d)
Develop vaccine for specific disease

Pasteurization is a process of sterilizing milk and it was
discovered by
a.
koch
b.
Louis
c.
Anton
d.
Newton

Write the exceptions of koch’s postulates

Enlist the different branches of microbiology and their definition

Write the general characterstics of viruses

Write two infectious diseases caused by bacteria ,fungi, protozoa
and viruses