This document provides an introduction to medical microbiology for second year public health students. It defines key microbiology terms and outlines the history and development of the field. The document discusses the classification and morphology of microorganisms and provides information on bacterial structures and functions. It also summarizes the important contributions of scientists such as Pasteur, Koch, and others to establishing microbiology as a science.

1. MEDICAL MICROBIOLOGY
FOR 2nd YEAR
PUBLIC HEALTH STUDENTS
1

2. INTRODUCTION
TO MEDICAL MICROBIOLOGY
2

3. Learning objectives
At the end of this chapter students will be able to:
 Define what mean Microbiology and Medical Microbiology
 Scope of Microbiology
 Importance of Microorganisms
 Brief Historical background of Microbiology
 Taxonomy & classification of microorganisms
 Bacterial size, shape and arrangements
 Bacterial structures and function
 Bacterial nutrition
 Bacterial growth and generation time
 Mutation and bacterial gene transfer Mechanisms
3

4. Introduction
 Microbiology: deals with living organisms that are individually too small to be seen with
the naked eye.
 It considers the microscopic forms of life collectively referred to as microbes
 It deals also about their reproduction, physiology, and participation in the
process of nature, helpful and harmful relationship with other living things,
and significance in science and industry.
4

5.  Categories of microbe studied in microbiology
i. Acellular microbes (called nonliving infectious particles)
include prions and viruses.
ii. Cellular microbes (also called living microorganisms).
5

6. 1. Bacteria: Unicellular, prokaryotic organisms with no nuclear
membrane, mitochondria, Golgi bodies, or endoplasmic reticulum.
2. Fungi: Eukaryotic organisms that contain a well-defined nucleus,
mitochondria, Golgi bodies, and endoplasmic reticulum
3. Virus: Are the smallest infectious particles, ranging in diameter from
18 to 600 nm (mostly <200 nm)
4. Protozoa: Are the smallest parasites 1-2 µm in diameter (the size
of many bacteria)
 Microbes can be classified in four general groups:
6

7.  What is medical microbiology??
 Medical microbiology:
• Is the study of causative agents of infectious diseases of
humans and their reactions to such infections.
• In other words it deals with medical importance microorganisms
and there pathogenesis, laboratory diagnosis, specific treatment
and control of infections.
7

8. Sub divisions of microbiology
• Bacteriology–which deals with bacteria
• Virology–studies about viruses and prions
• Mycology–which deals with fungi
• Immunology–studies mechanisms of body protection against
pathogenic microorganisms
• Phycology–Which deals with Algae
• Protozoology–which deals with Protozoa
8

9. Scope of microbiology
 Microbiology is highly versatile science that involve in :-
• Medical Microbiology- human disease & warfare
• Veterinary Microbiology- Animal disease & probiotics
• Public Health Microbiology- in foods, water and beverages
• Industrial Microbiology-involve in production, bioremediation
• Pharmaceutical Microbiology-antibiotics production and testing
• Agriculture Microbiology-natural fertilizers, decomposing
• Plant Microbiology-plant disease and elemental cycle
9

10. Distribution of microorganisms in nature
 Microorganisms: can be found nearly everywhere as normal inhabitants
of the earth (biosphere).
 They exist in soil, water, air, food, on clothing, on the body etc.
 They survive in most unlikely environment like cold air, in hot springs
at temperatures of 900C.
 Inhabit the surface of living human and animal bodies and grow
abundantly in the mouth and intestinal tract.
10

11.  Only a small percentage of microbes are pathogenic, few are able to
cause disease.
 The others are considered beneficial or harmless, they cause disease
only if they got opportunity like accidentally invade or when the host
immunity is low “they are considered opportunistic”.
 Those microorganisms that live on the human body without causing
disease are called normal flora.
11

12. Microbes are Essential for Life on Earth:
a. Production of foods: wine, beer, soft drinks through fermentation
b. Photosynthesis: Algae and some bacteria capture energy from sunlight and
convert it to food
c. Decomposers: Many microbes break down dead and decaying matter and
recycle nutrients
d. Nitrogen Fixation: Some bacteria can take nitrogen from air and
incorporate it into soil.
e. Digestion: Normal flora in digestive tract are essential for digestion and
vitamin synthesis (Vitamin K and B)
f. Drug production: Penicillin and cephalosporin drugs
g. Genetic engineering: Creating genetically modified pesticide, protein, and
vaccine
h. Bioremediation: microbes used for clean up toxic pollutants through
break down of chemicals that would be harmful to other organisms
i. In medical research: Microbes are well suited for biological and medical
research.
12

13.  Microbes are responsible for two categories of
diseases:
1. Infectious diseases pathogens
2. Microbial intoxications (poising)
13

14. Historical Development of Microbiology
– Hippocrates, father of medicine, observed that ill health resulted due to
changes in air, winds, water, climate, food, nature of soil and habits of
people.
– Fracastorius (1500 G.C.): Proposed that the agents of communicable
diseases are living germs.
 However, microorganisms was seen for the 1st time under the
microscope in 1764.
– Anton van Leeuwenhoek observed “animalcules” in a drop of water.
• He was the first who properly described the different shapes of
bacteria.
14

15.  Following the discovery of Antony Van Leeuwenhoek “father of
Microbiology”, observed “animalcules”
 Question were raised - where did they originate?
 On the bases of this observation, two major theories were formulated.
1. Theory of Abiogenesis
2. Theory of Biogenesis
15

16.  Theory of Abiogenesis deals with the theory of spontaneous generation;
stating that living things originated “spontaneously” from non-living
things.
 (e.g. maggots from meat or mushrooms from rotting woods)
 Aristotle (384-322): The founder of a theory spontaneous generation.
 He observed spontaneous existence of fishes from dried ponds,
when the pond was filled with rain.
16

17.  Biogenesis “Life comes from life”: States that life comes from
pre-existing life
 Francesco Redi (1626-1697): He is the scientist who
first tried to set an experiment to disprove spontaneous
generation.
• He put the meat in a bottle and covered it with a gauze.
Observation
1) Unsealed – maggots on meat
2) Sealed – no maggots on meat
3) Gauze – few maggots on gauze, none on meat
As a result, scientists began to doubt Aristotle’s theory
17

18. John Needham (1749)
 Performed experiments similar to Redi’s
 Puts broth in flasks, some were sealed with corks, and some were
not.
 All flasks became cloudy, result different from Redi’s experiment.
 He suggested that life originate spontaneously from non-living
matters
• Introduced the first culture medium for microbial growth.
• Utilized infusion broth prepared by boiling meat, grain, etc.
18

19. Lazzaro Spallanzani (1776)
 Repeated Needham’s experiments to disproof spontaneous generation in
microscopic life.
 Boiled broth after placing in flasks.
 Sealed flasks by plugging with solid stopper.
 Results more consistent with Redi’s.
 Not accepted by spontaneous generation supporters, because they said
that “heating may have destroyed, degraded “vital force” and air was not
allowed to enter”.
19

20.  Louis pasture (1822- 1895) was the scientist who disproved the
theory of abiogenesis once and for all.
 Performed experiment to disprove Theory of spontaneous
generation.
 He designed a large curved flask/swan-necked (pasture goose
neck flask) and placed a sterile infusion broths.
 Flasks remained sterile unless tilted or neck broken.
20

21. • In ‘A’ air freely moved through the tube, but dust particles were
trapped in the curved portion of the flask. And no microbial growth was
observed.
.
21

22. • Therefore, Pasteur proved that microorganisms entered to the broth with
the air and micro organisms did not evolve spontaneously.
22

23. Major contribution of Louis Pasteur
• Microbial theory of fermentation: is a way of getting energy without
using oxygen (anaerobic).
• Principles and practices of sterilization and pasteurization.
 Pasteurization: routinely used on milk to eliminate pathogens as bovine
tuberculosis and brucellosis.
• Development of vaccines against anthrax and rabies
• Discovery of Streptococci
23

24. The golden age of Microbiology (1857- 20th century)
• Begun with the work of Louis Pasteur (“why wine turned sour?”)
Experiments:
• Grape juice without yeast no fermentation
• Grape juice + yeast fermentation only
• Grape juice + Yeast + Bacteria fermentation & sour
• Pasture suggested heating the grape juice will destroy all evidence of life
and used to preserve its freshness of juice, which is known as
pasteurization.
24

25. • Electron microscope invented – could see viruses for the first time!
 Beginning of modern virology
• Antibiotics discovered- birth of chemotherapy in 1910
– Paul Ehrlich 1st antibacterial agent against spirochetes
– Alexander Fleming penicillin in 1928.
• Genes beginning to be studied
 Birth of genetic engineering
• Another major discoveries of microbiology during golden age
25

26. – Vaccination and the establishment of immunology
• In 1796, Edward Jenner was the first to “vaccinate” people
against smallpox.
– Aseptic Technique –great idea
• Joseph Lister (1827 - 1912) is surgeon who explained sepsis
and discovered antiseptics for the 1st time.
– He is called the father of antiseptic
» He used a chemical disinfectant phenol (carbonic acid)
to prevent surgical wound infections
26

27. The Germ Theory of diseases
 Pasture has developed the germ theory of diseases, which states that “a
specific disease is caused by a specific type of microorganism”.
• Stands from idea of Fracastorius
 Then Robert Koch, in 1876 established an experimental procedure to
prove the germ theory of disease.
 The scientific procedure is known as Koch’s Postulate.
27

28.  A Micro-organism can be accepted as a causative agent of an
infectious disease only if the following conditions are satisfied.
1. The causative agent of the disease must be present
in every diseased animal
2. The organism can be isolated from the diseased
animal and grown in pure culture
3. The pure culture will produce the disease when
inoculated into a susceptible animal
4. The same infectious agent must be re-isolated from
the experimentally infected animal.
Koch’s Postulate:- proof of germ theory of disease
28

29. 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. E.g.. Treponema pallidum.
 Many pathogens are species specific. E.g.. Brucella abortus cause
abortion in animals but not in humans.
 Certain diseases develop only when an opportunistic pathogen
invades immuno-compromised host.
29

30. Major achievements of Robert Koch
1. Discovery and use of solid medium in bacteriology
2. 1875-identified the germ for anthrax.
3. 1882-discovered the germ for tuberculosis (TB)
4. 1883-discovered the germ for cholera.
30

31. 2. Taxonomy and Classification
of Microorganisms
31

32.  Taxonomy and classification of microorganisms
1. Taxonomy: is the science of classification, identification, and
nomenclature.
 Hierarchy of Taxonomy Rank: Kingdome, Phylum, Class, Order, Family,
Genus, and Species
2. Classification: is the orderly arrangement of organisms into
groups with different criteria.
 There is nothing inherent about classification
 Different groups of scientists may classify the same organisms
differently.
32

33. 3. Identification:
– is the practical use of classification criteria to distinguish certain
organisms from others,
4. Nomenclature (naming):
– is the means by which the characteristics of a species are defined
and communicated among microbiologists.
– A species name should mean the same thing to all microbiologists
33

34.  Binomial nomenclature includes:
I. Genus comes before species (e.g., Escherichia coli)
II. Genus name is always capitalized (e.g., Escherichia)
III. Species name is never capitalized (e.g., coli)
IV. Both names are always either italicized or underlined
(e.g. Escherichia coli)
V. The genus name may be used alone, but not the
species name (i.e. saying or writing “Escherichia”
alone is legitimate while saying or writing “coli” is
not)
34

35. Criteria for microorganisms classification:-
• Classification can be phenotypic, genotypic or analytic
1. Phenotypic- Morphology (shape, size, stain reaction, cell structures) and
Biochemical activity (detection of presence or absence of particular enzymes
or metabolic pathways)
2.Genotypic classification- Composition of guanine and cytosine, DNA
hybridization, Nucleic acid sequence analysis, Plasmid analysis, Ribotyping
(analysis of rRNA genes)
3.Analytic classification-Is based upon detection of structural components and
metabolic products such as:- cell wall fatty acids, whole cell lipids, whole
cell proteins and Enzymes.
35

36. Classification criteria for bacteria
1. Morphology
2. Motility
3. Staining
4. Growth
5. Nutritional requirement
6. Bio chemical and metabolic activity
7. Pathogenicity
8. Amino acid sequencing of proteins
9. Genetic composition
36

37. 3. Bacterial Morphology, Size, Shape and
Arrangements
37

38. o Morphology: - Bacteria vary widely in size, ranging from 0.2
um to 10um long
• There are three basic shapes
1. Spherical or cocci- (singular –coccus)
2. Rods or bacilli- (singular - bacillus)
3. Spirals or spirilla- (Singular - Spirillum)
38

39. • The cells of cocci may be found in various
arrangements depending on the species and the way
they divide
– Micrococcus-Cocci occurring singly
– Diplococci-Pairs of cocci
– Strepto cocci – Cocci in chain
– Staphylococci- Cocci in cluster
– Tetrads – Four cocci as in box
– Octads (sarcina) – Eight cocci
39

40. 40

41. 4. Bacterial structures and function
41

42. Basic features of Bacterial Cell
• General property
– Typical prokaryotic cell
– Contain both DNA and RNA
– Most grow in artificial media
– Replication is by binary fission
– Contain rigid cell wall
42

43. Prokaryotic cells
– Most have haploid (single) and circular chromosomes
– Has no true nucleus and membrane bound organelles
– The nuclear body is called a nucleoid
– Histones are not present to maintain the conformation of the
DNA, and the DNA does not form nucleosomes
– The cell usually divides by binary fission
43

44. • Major characteristics of Eukaryotes &Prokaryotes
44

45. The structure of bacterial cell
• Considered at three levels.
o Cell envelope proper: Cell wall and cell membrane
o Cellular elements enclosed with in the cell envelope:
Mesosomes, ribosome, nuclear apparatus, polyamies and
cytoplasmic granules.
o Cellular element external to the cell envelope:
Flagellum, Pilus, Capsule or slime layer, and spore.
45

46.  Function of cell wall
– Provide rigid support for the cells and protect the fragile
cytoplasmic membrane
– Gives regular shapes for bacteria
– Contain strong activator of immune response
– Crucial for growth and division
– Components are unique to bacteria and used for
classification
46

47.  Function of Cell Membrane
– Regulates the transport of nutrients and waste products into and out
of the cell.
– It is selectively permeable
– Assists DNA replication
– Captures energy in ATP
 Function of Cytoplasm
– Containing a variety organic and inorganic solutes
• Water, enzymes oxygen, waste products, essential nutrients,
proteins, carbohydrates, lipids and a complex mixture of all the
materials required by the cell for its metabolic functions.
47

48.  Function of Mesosomes
– Are attached to chromosomes and are involved in DNA segregation during
cell division
– Involved in to secretion of proteins and active transport
– It is involved in respiratory enzyme-activity.
• Site of oxidative phosphorylation
 Function of Ribosomes
– Are the sites of protein synthesis
– It is composed of ribosomal RNA (rRNA) (70%) and proteins (30%)
– Prokaryotic ribosomes are 70S in size, being composed of Small (30s) and
Large ribosomal (50s) subunits.
– Where S stands sedimentation coefficient of the rRNA
48

49.  Function of plasmids
– Plasmids carry the genes for production of
• Antibiotic resistance
• Resistance to heavy metals
• Resistance to ultraviolet light
 Function of Pili (fimbriae)
– Mediate the adherence of bacteria to epithelial cells
49

50. Types of cell wall
I. Gram positive cell wall of bacteria
– Has multiple layers of Peptidoglycan (PG) cross linked with teichoic acid.
– The PG layer comprises 50 – 90% of the cell wall and 20 – 40% of the cell
wall weight
– Teichoic acids and cell wall- associated protein are the major surface
antigens of the Gram- positive cell wall.
– The large amount of peptidoglycan make Gram- positive bacteria
susceptible to the enzyme lysozyme and penicillin.
– Penicillin specifically inhibits peptidoglycan synthesis
50

51. II. Gram negative Cell wall of bacteria
• Is some what complex with thin peptidoglycan layer
• Has high lipopolysaccharide in the outer membrane
• Has periplasmic space.
 Outer membrane
– Contains receptors (sites) for attachment
– It participates in cell division and used in transport of materials
 Lipopolysaccharides
– Responsible for antigenicity of the outer membrane
• Powerful stimulator of immune response
– Serves as a bacterial endotoxin
 Periplasmic space
– Found between outer membrane and the cell membrane
– Mostly contain enzymes and endotoxin. 51

52. • A: gram positive bacterium, B: gram negative bacterium
52

53. III. Acid fast cell wall
– Resemble Gram positive cell wall
– Acid-fast bacteria have a cell wall with a relatively
impermeable containing a waxy lipid called mycolic acid
– Mycolic acids confer resistance to
• Desiccation
• Most antibiotics
• Phagocytosis
• Contributes to pathogenicity
53

54. IV. Bacteria with defective cell walls include:
– Mycoplasma: Highly pleomorphic bacteria naturally lacks
cell wall
– Protoplasts: Derived from Gram-positive bacteria and
totally lacking cell walls
– Spheroplast: Derived from Gram-negative bacteria non-
functional cell wall material
– L-forms: Cell wall-deficient forms of bacteria usually
produced in the laboratory
54

55. 5. Bacterial Nutrition, Growth, Metabolism
and Generation time

56. Nutrition
• For optimal growth and multiplication, bacteria requires
nutrients, such as water, energy, carbon, nitrogen and some
inorganic salts.
• All bacteria need some form of the element Carbon, H, O2, S,
P, and N for growth.
• In most case, bacteria need small amount of salt
concentration to grow.
– Halophytes are bacteria which need high concentration of
salt for their growth.
56

57. 1. Nutrient requirement
• Depending on their nutritional requirement bacteria can be
classified primarily based on the source of carbon
• Autotrophs: - are free-living, non-pathogenic bacteria, most
of which can use carbon dioxide as their carbon source such
as the cyanobacteria.
• Heterotrophs:- are generally parasitic bacteria
– Human pathogenic bacteria are heterotrophs
– The principal source of carbon is carbohydrate
• Degraded either by oxidation in the presence of oxygen or by
fermentation in the absence of oxygen
57

58. 2. Temperature requirement
• Most pathogenic bacteria grow best at an optimum
temperature of 370C.
• Psycrophylic- are those bacteria, which grow in the range of -
5 to 200C
• Mesophilic- which grow at 20-450C and show optimum
growth at 37oC.
– pathogenic bacteria belong to this group.
• Thermophilic – are those organisms which prefer high
temperature (50-800C)
• Hyper thermophilic: those which grow at a temperature of
above 800C
58

59. 3. Oxygen requirement
Bacteria have been divided in to:
• Obligate Anaerobes-these grow only in the environment
devoid of oxygen. e.g. Clostridium
• Facultative aerobes- these can grow under both aerobic
and anaerobic conditions, e.g. enterobacteriacae
• Obligate aerobes- these cannot grow unless oxygen is
present in the medium, e.g. pseudomonas
• Microaerophilic- these organisms can grow under
conditions with low oxygen tension e.g. Clostridium tetani.
59

60. 4. pH requirement
• Most pathogenic bacteria require a pH of 7.2-7.6 for their
optimal growth.
• Neutrophilic:- bacteria grow best at neutral pH (pH=7)
• Acidophilic: Bacterial grow best at acidic pH (pH<7) E.g.
Lactobacilli, fungi and yeast
• Alkalophilic: grow best at Alkaline pH (pH>7)
– E.g. Vibrio cholerae grow at a pH of 8.6
60

61.  Bacterial Metabolism
• Involves all the cellular processes required for the
survival and replication of the organism.
• Refers to all of the chemical reactions occurring
within a cell, including the production of energy,
intermediate products, and end products.
• Most biochemical reactions fall into two categories:
Catabolism and Anabolism.
61

62. o Catabolism: involve the breakdown of bonds of organic
compounds that results in the production of energy and
smaller molecules.
o Anabolism: involves the creation of bonds
– Refers to biosynthetic processes that use energy for the
synthesis of protoplasmic materials needed for growth,
maintenance, and other cellular functions.
– Smaller molecules are bonded together to create large
molecules
62

63.  Bacterial growth
– Bacteria divide by binary fission: when a bacterial cell
reaches a certain size, it divides to form two daughter
cells under optimum conditions.
– The generation time of bacteria ranges from as little as 20
minutes for E. coli to more than 20 hrs for MTB.
The generation time varies not only with the species
but also with the amount of nutrients, the temperature,
the pH, and other environmental factors.
63

64. Bacterial growth curve
• The growth cycle of bacteria has four major phases.
1.The Lag Phase: is a short duration in which bacteria
adapt themselves to new environment
– This is a period of active macro molecular synthesis like
DNA, RNA, various enzymes and other structural
components
– It is the preparation time for reproduction
– Increase in size
– No increase in cell number occurs
64

65. 2. The log, or exponential phase: the population can double
approximately every 30 minutes
– It has limited duration because of:-
• Exhaustion of nutrients
• Accumulation of toxic metabolic end products
• Rise in cell density, Change in pH and
• Decrease in oxygen tension
– This phase is highly sensitive for antibiotic
65

66. 3. Stationary Phase:
– It is almost a balance between the bacterial
reproduction and bacterial death
– Occur when nutrients depletion or toxic products cause
growth to slow
4. The death/decline phase:
– Due to depletion of nutrients and accumulation of toxic
end products
– The number of bacteria dying is much more than those
dividing
– There is drastic decline in viable cells.
66

67. • Factors that affect bacterial
growth in vitro
• Nutrition
• Temperature
• Oxygen
• PH
• Salinity
• Osmotic pressure
• Light Radiation
67

68. Cultivation of bacteria
• Using artificial media
– Simple and complex media
– Basic and enriched/enrichment media
• Process of cultivation is:
– Culture media preparation
– Inoculation
– Incubation
– Reading and biochemical characterization

72. Continuous-culture
• To maintain a culture in exponential, steady-state (balanced)
growth for long periods is to use a device in which fresh medium
is continuously added but the total volume of culture is held
constant by an overflow tube.
• One such constant-volume device is called a chemosta
– it operates by infusing fresh medium containing a limiting nutrient at a
constant rate, and the growth rate of the cells is set by the flow rate
• A similar constant-volume device is the turbidostat
– it operates by the infusion of fresh medium by a pump controlled
indirectly by the turbidity of the culture
• Most of the places in which bacteria live on and within our
bodies, in health and disease, provide conditions more closely
resembling those of nutrient-limited continuous culture devices
than of enclosed flasks.
• Subculturing to new media

73. Fig. continuous-culture device

74. 6. Bacterial Genetics, Mutation and Gene
Transfer Mechanisms

75. Bacterial genetics
•Most of the genetic information in a bacterial cell is contained
with in chromosome
•Bacterial inherited characteristics are encoded in DNA
(Chromosome or Extra chromosome (Plasmid))
•Chromosome: Bacterial chromosome is circular double
stranded DNA attached to bacterial cell membrane
75

76. •Plasmids: are self replication extra chromosomal DNA
molecules.
•Plasmids are not essential to the life of the cell but
they may have selective advantage:
Virulence plasmids: carry virulence determining
genes
Resistance plasmids (R factor): code for drug
resistance genes
76

77. • DNA replication: The identical
duplication process
• Transcription: Genetic nucleotide
sequence is transcribed into mRNA
• Translation: Transformation of the
nucleotide sequence into the
polypeptide amino acid sequence
• Carried by the mRNA
77
Central dogma

78. 78

79.  Genetic Variation in Bacteria
• Can occur at molecular level or intercellular level
1. Molecular Mechanism
• Bacterial mutation occur when the information in a bacterial chromosome is
altered
• There are two types of mutation
 Spontaneous mutation: takes place in nature with out human
intervention or identifiable causes
 Induced mutation: caused by exposure to chemical or physical agent,
exposure to UV light etc.
79

80. 2. Intercellular Mechanisms of Genetic variability
• Gene transfer: there are three types of gene transfer that alter the DNA
gene content of bacteria
 Transformation, Transduction and Conjugation
• Transformation: occurs when fragment of exogenous DNA is absorbed in
to recipients bacterial cells
• Transduction: transfer of DNA from a donor to a receptor with the help of
transport bacteriophages
• Conjugation: occurs when plasmid DNA is transferred form donor to
recipient bacterium by direct contact via sex pilli
80

81. • Transduction of chromosomal DNA (A) and Plasmid (B)
81

82. • A: connection b/n two bacterial by sex pili; B: formation of specific conjugal
bridge; C: Plasmid mobilization &transfer; D: Synthesis of DNA strand
82

83. 83

84. Any questions?
84