This document provides an introduction to medical microbiology. It defines key terms related to bacteriology, virology, parasitology, mycology, and immunology. The history of microbiology is discussed, focusing on pioneers like Van Leeuwenhoek, Pasteur, Koch, Ehrlich, Lister, and Fleming. The relationship between microbes and hosts is explained, including normal flora, pathogens, opportunistic pathogens, and virulence. The transmission of infection is summarized, covering portals of entry/exit and means of transmission. The process of pathogenesis is outlined.

1. INTRODUCTION OF MEDICAL
MICROBIOLOGY
PRESENTED BY
MEGHA SHRIDHAR

2. INDEX
• DEFINITION
• HISTORY
• HOST-MICROBE
RELATIONSHIP

6. BACTERIOLOGY
Bacteriology is the branch and
specialty of biology that studies the
morphology, ecology, genetics and
biochemistry of bacteria.

7. VIROLOGY
Virology is the study of viruses and including their
taxonomy, disease-producing properties,
cultivation and genetics.

8. PARASITOLOGY
Parasitology is the study of parasites, their
hosts, and the relationship between them.

9. MYCOLOGY
Mycology is the branch of biology concerned
with the study of fungi.

10. IMMUNOLOGY
Immunology is the study of the immune
system. The immune system protects us
from infection through various lines of
defence.

11. RECOMBINANT DNA
TECHNOLOGY
Recombinant DNA technology refers to the
joining together of DNA molecules from two
different species that are inserted into a host
organism to produce new genetic
combinations.

12. HISTORY

14. ANTONY VAN LEEWANHOEK
(1632-1723)

15. LOUIS PASTEUR
(1822-1895)
(FATHER OF MICROBIOLOGY)
• Discovered Spontaneous
generation theory of
microbes.
• Originated the process of
pasteurization &
Fermentation;
• Developed vaccines
against anthrax against
Smallpox and rabies.

16. SPONTANEOUS GERM THEORY

17. ROBERT KOCH
(1843-1910)
(FATHER OF BACTERIOLOGY)
• Experimental approach to
prove Germ Theory of Disease,
which is known as Koch's
Postulates.
• He identified the specific
causative agents of anthrax,
tuberculosis and cholera.
• He introduced methods for
isolation of bacteria in pure
culture.

18. KOCH POSTULATES

19. PAUL EHRLICH
(1854-1914)
(FATHER OF CHEMOTHERAPY)
His laboratory discovered arsphenamine
(Salvarsan), the first effective medicinal
treatment for syphilis, thereby initiating
and also naming the concept of
chemotherapy. Ehrlich popularized the
concept of a magic bullet.
He invented the Staining technique for
Gram staining bacteria.
The methods he developed for staining
tissue made it possible to distinguish
between different types of blood cells,.

20. JOSEPH LISTER
(1827-1912)
FATHER OF ANTISEPTIC SURGERY
He successfully introduced
carbolic acid (now known as
phenol) to sterilize surgical
instruments and to clean wounds.
it became the first widely used
antiseptic in surgery.

21. ALEXANDER FLEMING
(1881-1995)
Discovery of penicillin

22. HOST-MICROBE
RELATIONSHIP

23. RELATIONSHIP
• Microbes are found everywhere. On a daily basis we
ingest, inhale, and transport thousands of organisms
(i.e., bacterial, viral, protozoa or parasitic).
• Most have no ill effects due to protective mechanisms
in our body (i.e., coughing, urinating, sneezing, and
defecating).
• Humans and animals have “friendly” organisms
throughout their bodies that survive as normal flora
and colonize a host but do not cause disease.
• However, if these organisms begin to cause any
damage to a host by invading tissues and/or producing
• toxins, they then become pathogens.

24. MICROBES & TYPES
Microbes: These are tiny living things that are found all
around us and are too small to be seen by the naked eye.
They live in water, soil, and in the air. The human body is
home to millions of these microbes too, also called
microorganisms. It is 2 types according to relationship.
a) Saprophytes: A plant, fungus, or microorganism that
lives on dead or decaying organic matter, found in soil
and water.
b) Parasites: An organism that lives on or in an organism of
another species, known as the host, from the body of
which it obtains nutriment.

25. RELATED TERMS
a) COMMENSALS: Living in a relationship in which one
organism derives food or other benefits from another
organism without hurting or helping it. Example:
Staphylococcus epidermidis on skin, Escherichia coli in
gastrointestinal tract.
b) PATHOGENS: A bacteria, virus, or other microorganism that
can cause disease in a host.
c) Mutualism: In mutualism, both the microorganism and the
body work together. An example of this relationship would be
cows and the bacteria in their rumen.
d) Opportunistic pathogens: Produces disease when host
immune system is low.
e) Pathogenicity: Ability of microbes to produce disease.
f) Virulence: Degree of pathogenicity of microbes.

26. INFECTION & ITS TYPES
Infection: The invasion and multiplication of microorganisms such
as bacteria, viruses, and parasites that are not normally present
within the body.
Types are as follow:
a) Primary infection: harmful effect by parasite in the body of
host.
b) Reinfection: Subsequent infection by same parasite again.
c) Secondary infection: When the body resistance is lowered by a
pre-exiting infectious disease, a new parasite affects.
d) Cross infection: When a patient already from a disease
acquires a disease acquire new infection from another from
another host.
e) Nosocomial Infection: Cross infection acquired in hospitals in
called hospital-acquired or nosocomial infection.

27. Continued..
f) Iatrogenic infection: Iatrogenic infection was defined
as an infection after medical or surgical management.
g) Sub-clinical infection: Infection which do not show
any sign and symptom. Example: Diabetes
h) Latent infection: Some parasite remain hidden or
latent in host tissue, when host immune system is
lowered causes clinical disease.

28. HOW RELATIONSHIP
WORKS?

29. NORMAL FLORA
Normal flora are the microorganisms that live on another living
organism (human or animal) or inanimate object without
causing disease.
The body contains two types of normal flora:
1) Resident flora (survive for extended periods)
2) Transient flora (temporary).
Normal flora help to provide defenses against invading
pathogens:
a) By covering adherence sites,
b) Producing compounds toxic to other organisms,
c) Preventing pathogens from consuming nutrients.

30. Host Defense
A microorganism will not be able to invade unless it
overcomes an animal’s or individual’s host defenses.
Specific host defenses may include:
• Skin and mucosal secretions
• Non-specific local responses (e.g., pH)
• Non-specific inflammatory responses
• Specific immune responses (e.g., lymphocytes)
The ability for a pathogen to overcome host defenses
can be accomplished by two distinct components: a
primary pathogen (causes disease in a healthy host) or
opportunistic pathogen (causes disease if host is immuno-
compromised).

33. Pathogen Defenses
Pathogens contain virulence factors that
promote disease formation and provide the
opportunity for a microbe to infect and cause
disease.
The greater the virulence, the more likely disease
will occur. Such factors include:
• Ability of a pathogen to adhere to a host
• Ability of a pathogen to colonize (overcome) a
host
• Ability of a pathogen to evade host defenses

34. TRANSMISSION OF INFECTION

35. Portal of entry
In order to begin infection and eventually
cause disease, pathogens must find a
transmission route.
Transmission of an infectious agent can occur
in many ways:
Through exposed skin (e.g., a cut, abrasion,
puncture, or wound)
mucous membranes (e.g., gastrointestinal
tract, respiratory tract, or urogenital tract)

37. Means of transmission:
1. Blood borne: through sexual transmission, injury or inoculation
or blood splashes.
2. Airborne: through inhalation of small particles that remain
suspended in the air for long periods of time .
3. Droplet: also through inhalation. Spread is through close
contact with infected persons who may be sneezing, coughing,
talking.
4. Contact: through direct or indirect contact. Direct is the transfer
of organisms by contact with contaminated hands. Indirect is the
transfer or organisms through fomites
5. Common vehicle: through food, water, drugs, blood or other
solutions
6. Vector borne: usually through arthropods such as mosquitoes
and ticks but cockroaches, ants and flies can also transmit
infection.

39. Reservoir
Where microorganisms can be found. Within
healthcare settings this may include:
1. The environment e.g. dust, bedding,
equipment, furniture, sinks or washbowls,
bedpans, surfaces)
2. Humans, including patients, staff and visitors,
especially from hands.

40. Pathogenesis
Pathogenesis can also occur by pathogens invading
and breaching the body’s barrier in order to
multiply. These organisms have mechanisms that
will not allow macrophages (the body’s defense
against pathogens) to destroy them.
a) Adherence: Attaching itself to the host’s tissues.
This attachment is called adherence and is a
necessary step in pathogenicity. Microbes
contain ligands, which are projections that
attach host receptors or surface proteins.

41. b) Invasion: Microbes begin to invade the host and
produce a bacteremia (i.e., presence of bacteria in
the bloodstream) or viremia (presence of a virus in
the bloodstream).
c) Colonization: Colonization is the multiplication of
pathogenic organisms where toxins are produced
and the normal flora are overcome.
During this stage, pathogens compete with normal
flora for space and nutrients.
Pathogens usually colonize host tissues that are in
contact with the external environment.
During colonization, the host begins to show signs
of septicemia (i.e., blood infection where bacteria
are reproducing).

42. d) Cause Damage: Damage can occur through direct or
indirect pathways. Direct methods produce toxins,
which are poisonous substances that produce toxemia
within a host.
Three types of toxins are produced to cause damage:
• Exotoxins: Proteins secreted by pathogens that
cause damage to the host (botulinum toxin, tetanus
toxin, hemolysin (ruptures red blood cells).
• Endotoxins: Toxic substances that are released when
a cell is killed (Lipolysaccharides).
• Exoenzymes: Enzymes that function outside the host
cells or tissues. These include coagulase (forms a
fibrin clot that “hides” the microbe from
phagocytosis), hyaluronidase (breaks connective
tissues down), or fibrinase (breaks down blood clots
to allow pathogens to continue spreading).

44. Portal of exit
These are required for microorganisms to be transmitted from human
sources.
Portals of exit within healthcare settings include:
• urinary catheters,
• wound sites,
• open skin lesions,
• skin, and mucous membranes.
• Semen
• Urine
• Stool
• Sneeze
• Cough
• Saliva
• sputum