This document provides an overview of medical microbiology. It begins with definitions of microbiology and its branches. Microorganisms can be found nearly everywhere and most contribute to human well-being, though some cause disease. The document then discusses the history of microbiology and contributions of scientists like Pasteur and Koch. It also covers host-pathogen relationships, types of microorganisms, and important concepts in microbiology.

1. Edna Adan University
• Chapter one
• Medical Microbiology
Barkhad Ahmed Abdilahi
(MLT.Mph)

2. Outline …
Definition and brief history of microbiology
Terminologies in microbiology
Classification of microorganism
The infection process

3. Introduction
 The world micro means very small, anything so small that it must be
viewed with a magnifying glass, the microscope
 Bios means living organisms and logos means study of
 Therefore, microbiology is the study of very small living organisms
(microscopic size).
 The term was introduced by the French chemist Louis Pasteur.
 The microbes of medical importance include protozoa, fungi, bacteria
and viruses

4.  Micro organisms can be found nearly every where
 Normal inhabitants of the earth and with few exceptions; they
contribute to the well fare of humans.

5. Where do microorganisms found
 . The indigenous micro flora that live on and within our bodies actually
inhibit the growth of pathogens by:-
 Occupying the space
 Using the food supply , and
 Secreting materials(waste products, toxins, antibiotics) that may
prevent or reduce the growth of pathogens.
 Other non-pathogens make it possible to produce yogurt, cheese,
raised bread, beer wine and many other foods and drinks.

6. Branches of Microbiology
 Bacteriology- which deals with study of Bacteria
 Mycology- which deals with study of Fungus
 Parastology- which deals with study of Protozoology &
Helminthological
 Virology- which deals with study of Viruses

7. General Microbiology
:-the study and classification of micro
organisms and how they function is known as
general microbiology. It includes all areas of
microbiology.

8. Medical Microbiology: - involves the study of
Pathogens and
 Epidemiology, transmission of
pathogens, disease prevention
measures, aseptic techniques, and
treatment of infectious diseases,
immunology and the production of
vaccines to protect against
infectious disease diseases.

9. Industrial Microbiology.
Food and beverage industries,
pharmaceutical industries relies on
microorganism therefore
Industrial microbiologists monitor and
maintain the essential micro organisms for
these commercial enterprises.

10. Distribution of microorganisms
 Microorganisms can be found nearly everywhere as normal
inhabitants of the earth.such as
A. Air
B. Soil
C. Water
D. Animals
E. Human body

11. .cont….
 Actually only a small percentage of microbes are pathogenic,
few are able to cause disease.
 The others are considered beneficial or harmless, or they cause
disease only if they accidentally invade the wrong place at the
right time such as when the host immunity is low. These
microbes are considered opportunistic.
 Most of this Microorganisms that live on the human body with
out causing disease and apparent physiological response are
called normal flora.

12. Microorganisms and Human Beings
 Beneficial activities: Most microbes are of benefit to human
beings, some are necessary(E.coli enhances digestion and
vitamin k synthesis)
 Harmful activities: A portion of microbes cause diseases and
are poisonous to human, and these are really that concern us in
the study of Medical Microbiology, etc.

13. The Importance of Microbiology
A. Environment
B. Medicine
C. Food
D. Industry
E. .Research

14. The Importance of Microbiology
 Humans & many other animals depend on the microbes in their
intestines (microflora) for:
 The digestion & the synthesis of some vitamins that their
bodies require
 some B vitamins = metabolism
 vitamin K = blood clotting

15. The Importance of Microbiology
Environment: microbes
used to treat sewage and clean up
pollution
 Bioremediation (BIOLOGICAL
Microorganisms to solve
environmental problem, such as
contaminated soil or ground
water .

16. Some microorganisms are used in commercial & industrial
application
Industry: Chemicals ---organic acids ,enzymes & alcohol
(ethanol, acetone, etc.)
Food: cheese, yogurt, bread, pickles & vinegar
Drugs --- antibiotics (penicillin)

17. Modern Biotechnology & Recombinant DNA technology
Biotechnology : practical application of
microbiology to produce some common foods &
chemicals
•Recombinant DNA technology: have been
used to produce a number of natural proteins
vaccines & enzymes
•Gene therapy: inserting missing gene or
replacing defective one in human cells, harmless
virus to carry gene

18. The History and Scope of Microbiology
today we understand that microorganisms are found
almost everywhere
before the invasion of the microscope microbes were
unknown to scientist
thousands of people died in devastating
epidemics,(rapid spread of infectious disease large
number of people) the causes of which were not
understood
entire families died because vaccination & antibiotics
were not available to fight infections

19. The History and Scope of Microbiology
we can get an idea of how our current concepts of Microbiology
developed by looking at a few of the historic milestones in
Microbiology that have changed our lives

20. History of Microbiology
 Experience phase
 Experimental phase
 Modern phase

21. HISTORICAL BACKGROUND
Man kind has always been affected by diseases which
were originally believed to be visitations by the gods and
meant to punish evil doers
Hippocrates, father of medicine, was Greek physician
was observed that ill health resulted due to changes in
air, winds, water, climate, food, nature of soil and habits
of people.
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22.  Fracastorius (1500 G.C.) proposed that the
agents of communicable disease were living
germs, that couldbe transmitted by direct
contact with humans and animals, and indirectly
by objects ; but no proof because of lacking
experimental evidence.
 Antony Van Leeuwenhoek (1632-1723 G.C.),
father of Microbiology, observed
“animalcules”(an old term of microscopic
animal or protozoan. using his simple
microscope with one lens.
He was the first who properly described the 22

23. Theory of A biogenesis
living things originated from non-living things.
Aristotle (384-322 BC): The founder of a theory
spontaneous generation. He observed spontaneous
existence of fishes from dried ponds, when the pond
was filled with rain.
Francesco Redi (1626-1697): He is the scientist who
first tried to set an experiment to disprove spontaneous
generation.

24. Theory of Biogenesis
States that life comes from pre-existing life.
Louis Pasteur (1822-1895 GC) was the
scientist who disproved the theory of
abiogenesis.

25. Other major contribution of Louis Pasteur.
 Microbial theory of fermentation (break down of
substance by bacteria yeast or other MOS
 Principles and practices of sterilization and
pasteurization (process of heating milk and food to kill
pathogenic bacteria)
 Development of vaccines against anthrax and rabies
 Discovery of streptococci.
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26. The Germ Theory of diseases
• Pasture has also developed the germ theory of diseases, which
states that “a specific disease is caused by a specific type of
microorganism”.
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27. • Robert Koch, in 1876 established an
experimental procedure to prove the germ theory
of disease, which states that specific disease is
caused by specific pathogen. The scientific
procedure is known as Koch’s Postulate.
R.Koch proof that for a specific disease there is a
specific microorganism responsible e.
Tuberculosis -------- M.tb
Cholera---------------------------------V.cholera
Thyphoid ------------------------------- S.thyphi

28. Koch’s Postulate: - proof germ theory of
disease
 A Micro-organism can be accepted as a causative agent of an
infectious disease only if the following conditions are
satisfied.
1. The microorganism should be found in every case of the
disease and under conditions, which explain the pathological
changes and chemical features.
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29. 2. It should be possible to isolate the causative agent in
pure culture from the lesion
3. When such pure culture is inoculated in to appropriate
lab animal, the lesion of the disease should be reproduced.
4. It should be possible to re-isolate the bacterium in pure
culture from the lesion produced in the experimental
animal.

30. Exceptions to Koch’s postulate
• Many healthy people carry pathogens but do not exhibit symptoms
of the disease.
• Some microbes are very difficult or impossible to grow in vitro (in
the laboratory) in artificial media. Eg. Treponema pallidum.
• Many pathogens are species specific. Eg. Brucella abortus cause
abortion in animals but not in humans.
• Certain diseases develop only when an opportunistic pathogen
invades imuno-compromised host.
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31. Major achievements of Robert Koch
1. Discovery and use of solid medium in
bacteriology
2. Discovery of causative agents of
tuberculosis and cholera
3. Koch’s postulate
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32. Epidemic: disease exist in excess of what we expect
Endemic: disease exist in small number with in a
population at all times
Pandemic: a world wide out break of an infectious
disease.
Incubation period: the interval between contact with the
microbeand pain . and the development of symptoms and
sign of infection
Infection: entry of a harmful microbe in to the body and
its multiplication in the tissues
Inflammation: a response to infection or other injury
characterized by swelling , heat , redness

33. Reservoir (of infection) : the permanent source of
infection; e.g foxes are reservoirs of rabies in western
Europe
Colonization: a microbe that establishes itself in a
particular environment such as a body surface with out
producing disease is said to ‘colonize “the site. Capable
of causing invasion and disease if virulent or if the host is
immunocompromized

34. Carrier: an individual who persistently excretes a
microbe or who has a body surface colonized by a
microbe, but who is not obviously ill of this infection.
Opportunistic organism : one capable of causing
infection when the immune system of the host is impaired

35. Normal Flora :These are a normal inhabitant that are
acquired early in life and reside in the human intestinal
track, skin, internal organ, body fluid.
Communicable versus non communicable.
A disease is communicable (contagious) if it is spread
from one individual to another Eg. MTB
A disease is non communicable when it cannot be
spread from one individual to another e.g. DM,
hypertension

36. Transmission………….
Vertical transmission of a disease refers to the spread of the
illness from mother to child either in utero or during the birth
process. Eg. Trepanoma palladium and Nessiria gonoria
respectively
Horizontal transmission refers to the disease spread from
one person to another by some means.
Transplacental transmission refers to the dissemination of a
microbe through the ovaries and hence the eggs.

37. Prokaryotes and Eukaryotes
Prokaryotic cells have a simpler structure and in particular
, the nuclear material is free with in the cytoplasm e.g.
bacteria
Eukaryotic cells have their DNA enclosed with in a
nuclear membrane , and a clear nucleus can be seen under
the microscope e.g. protozoa , fungi , blue green algae
Viruses are organism which require other living cells in
order to reproduce

38. Prokaryotic cell structure
Cell wall
Gives rigidity and preserve the shape of the organism
Serve as a means of protection for the organism
Enclose a thin flexible cytoplasmic membrane (plasma
membrane)
Allows diffusion to take place between the cell cytoplasm
and the environment

39.  Are liquid and include the following
The cytoplasm : contains the mechanisms necessary for
maintaining the cell and allowing reproduction
Nuclear material DNA – circular and double stranded ,
not bounded by a nuclear membrane
Ribosome :- numerous granules of RNA which
manufacture ( synthesize ) proteins
Mesosome :- granules which sometimes may be formed
by invagination of the cytoplasm membrane and act as a
respiration center

40. Eukaryotic cells
The cell membrane forms the outer boundary of the
eukaryotic cells except filamentous fungi
The cytoplasm is more complex than in prokaryotes cells
More distinct structures in the cytoplasm called organelles
, with the following specific functions

41. i. Nucleus –bounded by a double membrane and
containing DNA and nucleoli which are involved with
RNA production
ii. Endoplasmic reticulum :- the frame work for transport
of proteins ,lipids, and other materials
iii. Ribosome:- produce protein as in prokaryotes

42. iv. Mitochondria :- for respiration ( energy ) production “
Power house of the cell”
v. Golgi complex:- concerned with secretion of substance
from the cell
vi. Lysosome :- enzyme made in the golgi complex often
contained in small vesicle which can break down
foreign bacteria

43. HOST PARASITE RELATIONSHIP
Definition: It is a beneficial or harmful relationship between the
host and the parasite.
Is characterized by fighting of the organism to invade the
body and the body defending itself by protective measures.
Human host is in contact with many microorganisms called
normal flora or commensals but can cause disease and called
opportunistic pathogens.
Primary pathogens, strict pathogens or virulent bacteria
Non-Pathogenic bacteria, they will never cause disease

44. On the basis of their life habits, microorganism is classified as
 saprophytes or parasites.
Saprophytes : Mode of life of free-living organisms which
obtain their nourishment from soil and water. Saprophytes in general
do not require a living host.
Parasites: organisms living on or in other higher organisms.
types of parasites
ectoparasite : lives on surface of host
endoparasite :lives within host

45. The association may take one of the three forms
. Symbiosis: The ability to live in the tissues of the host with
mutual benefit. Neither of them are harmed.
:2. Commensalism The ability to live on the external or internal
surface of the body with out causing disease.
“Eating at the same table”.
3. parasitism: one ( the host) is harmed and the other(the parasite )
is benefited .

46. 4. Pathogencity:
Pathogenicity: The ability of an organism to cause disease.
The outcome of the host- parasite relationship depends on
a
balance between
 the virulence of the parasite and
 the resistance of the host.
Pathogenic parasites – microbes that have the potential to
cause disease.
Non-Pathogenic – microbes that do not cause disease under
normal circumstances.
Opportunistic parasites – microbes that can cause diseases
when the immune system of the host is suppressed.

47. General Concepts
Host Susceptibility
Resistance : The ability of the host to prevent establishment of infection by
using its defense mechanisms..
Initial resistance is due to nonspecific mechanisms.
Specific immunity develops over time.
Susceptibility :Lack of this resistance and establishment of disease.
Susceptibility to some infections is higher in the very young and the very
old and in immunosuppressed patients.
Bacterial Infectivity
 Bacterial infectivity results from a disturbance in the balance between
bacterial virulence and host resistance.
The "objective" of microbes is to multiply rather than to cause disease; it is
in the best interest of the bacteria not to kill the host.