This document provides an introduction to the topics that will be covered in a microbiology course, including definitions, history, and branches of microbiology. It discusses the normal microbial flora of the human body and their ecological relationships. Key topics include the germ theory of disease, Koch's postulates, the miasma theory, and host-pathogen interactions. The course will cover bacteria classification and structure, growth, pathogenicity, sterilization methods, staining techniques, and examining various clinical specimens.

1. Introduction to
Microbiology
BUGA RUDOLF
MakSPH

2. Teaching Objectives in introduction
• Define microbiology
• Give the scope of microbiology
• Explain importance of microbiology to man
• To give an overview of the history of Microbiology
• To list and give properties of pathogenic organisms

3. Topics in microbiology will include
– Introduction to microbiology
– Normal Flora of the human body
– Classification of bacteria
– Anatomy of a bacterial cell
– Bacterial genetics
– Bacterial growth
– Bacterial pathogenicity and virulence
– Sterilization and disinfection
– Staining

4. Topics
cont..
– Culture media
– Inoculation of culture media
– Incubation of bacteria
– Tests for identification of bacteria
– Sensitivity testing/antimicrobial sensitivity testing
– Processing of specimens
– Systematic bacteriology

5. Topics
cont..
• Public health bacteriology
• Examination of:
– Food and beverages
– Water and sewerage
– Milk
– Air

6. References
• Baker F. J. & Silverton R. E. (2001). Introduction to
Medical Laboratory Technology. 7th Ed. London.
Butterworths.
• Cheesbrough M. (2006). District Laboratory
Practice in Tropical Countries Part 2. 2nd Ed.
Cambridge: Cambridge University press
• AMREF (2003).Communicable diseases, a Manual
for Primary Health Care workers –
• 4. AMREF (2003). Practical Laboratory Manual
for Health Centres in Eastern Africa

7. References
• Madigan et al. Brock’s Biology of
Microorganisms : 9th, 10th eds.
• Prescott et al., Microbiology, 3rd, 4th eds.
• Black, Microbiology, 4th ed.
• Other Microbiology texts

8. Introduction
• “Microbiology’ - the study of microorganisms
• organisms too small to be seen with the naked eye
Except when in large groups (colonies)
• Effects of large numbers often visible
– Chemical reactions in soil horizons
– Toxin and gas production in incompletely sterilised food
cans
– Disease in animals and plants

10. Microbial World
• Viruses
• Bacteria,mycoplasma,
rickettsia, clamydia
• Fungi (Yeasts and
Molds)
• Protozoa
• Microscopic Algae
• Immune system
• Measures of disease

13. Branches of Microbiology
• Bacteriology: study of bacteria
• Protozoology: study of protozoa
• Algology: study of Microscopic Algae
• Epidemiology: study of Measures of disease
• Mycology: study of fungi

14. Branches of Microbiology….
• Immunology: study of immunity
–Edward Jenner, UK: developed vaccination
(1798)
–Metchnikoff, RU: discovered phagocytes
(1884)
–Paul Ehrlich, DE: theory of immunity (1890)
• Virology: study of viruses
–Beijerinck, NE: discovered intracellular
reproduction of TMV; coined the term
“virus” (1899)

15. Branches of Microbiology..
• Parasitology: study of protozoa and parasitic worms
• Chemotherapy
– Treatment of disease by using chemical means
– Antibiotics produced naturally
– Synthetic drugs
– Paul Ehrlich (1878) – used arsenic compounds to fight
disease – ‘magic bullet’

16. Branches of Microbiology…
• Chemotherapy
– Alexander Fleming, Scotland (1928) discovered
penicillin
– Selman Waksman, Ukraine (1944) discovered
streptomycin
• Problems
– Toxicity of drugs => Selective toxicity
– Resistance of bacteria to drugs

17. Branches of Microbiology…
• Recombinant DNA Technology
– Recombinant DNA
– Genetic engineering/biotechnology
– Microbial genetics – mechanism by which
microbes inherit genes
– Molecular biology – structure and function
(expression) of genes
– Molecular epidemiology/diagnostics

18. Branches of Microbiology…
• Biotechnology
– GMOs/GEMs for industrial, pharmaceutical and
agricultural applications
– Improvements of agriculture (plants and animals)
– Gene therapy: inserting a missing gene or replacing a
defective one in human cells

19. Benefits
• Maintain balance of environment (microbial
ecology)
• Basis of food chain
• Nitrogen fixation
• Photosynthesis
• Digestion
• Synthesis of vitamins
• Manufacture of food and drink

20. Benefits
• Genetic engineering
• Synthesis of chemical products
• Recycling sewage
• Bioremediation: use microbes to remove
toxins (oil spills)
• Use of microbes to control crop pests
• Normal microbiota

21. Harmful Effects
• Cause disease
• Basis for bioterrorism
• Destruction of materials
• Food spoilage

22. Historical perspective
Pioneers of Microbiology
• Robert Hooke, UK (1665) proposed the Cell
Theory, observed cork with crude microscope
coined theory
``All living things are composed of cells``
• Edward Jenner 1796 carried successful
vaccination for smallpox
• Spontaneous generation ``Some forms of life
could arise spontaneously from non-living
matter``
• Francesco Redi (1668) Redi’s experiments to
disapprove spontaneous generation

23. Pioneers of Microbiology
• Antoni van Leeuwenhoek, DE (1673) first to
observe live microorganisms (animalcules)
• Schleiden and Schwann, Formulated Cell
Theory: ``cells are the fundamental units of
life and carry out all the basic functions of
living things``
• Pasteur, FR and Tyndall, UK (1861) finally
disproved S.G.

24. Pioneers of Microbiology
• Louis Pasteur (1822-1895), Chemist
– Fermentation (1857)
– Pasteurization: heat liquid enough to kill
spoilage bacteria (1864)
– Rabies vaccine development
– Proposed the germ theory of disease
– Proposed aseptic techniques (prevent
contamination by unwanted microbes)
– Director of Pasteur Institute, Paris (1894)

25. Pioneers of Microbiology
• Joseph Lister, UK (1867) used phenol (carbolic
acid) to disinfect wounds. First aseptic
technique in surgery
• Robert Koch, DE (1876) Postulated the ``Germ
theory`` Identified microbes that caused
anthrax (1876), tuberculosis (1882) and
cholera (1883) Developed microbiological
media & streak plates for pure culture (1881)

26. The germ theory
• The germ theory of disease ``some diseases
are caused by microorganisms These small
organisms, too small to see without
magnification, invade humans, animals, and
other living hosts. Their growth and
reproduction within their hosts can cause a
disease``.

27. The germ theory cont..
• "Germ" may refer to a virus, bacterium, protest,
fungus, or prion. Microorganisms that cause
disease are called pathogens, and the diseases
they cause are called infectious diseases.
• Even when a pathogen is the principal cause of a
disease, environmental and hereditary factors
often influence the severity of the disease, and
whether a particular host individual becomes
infected when exposed to the pathogen.

28. Koch’s Postulates
• The specific causative agent must be found in every case of
the disease.
• The disease organism must be isolated from the lesions of
the infected case and maintained in pure culture.
• The pure culture, inoculated into a susceptible or
experimental animal, should produce the symptoms of the
disease.
• The same bacterium should be re-isolated in pure culture
from the intentionally infected animal.

29. Shortcomings of kochs postulates
• Koch's postulates may not hold if:
– The particular bacteria cannot be "grown in pure
culture" in the laboratory. E.g. leprosy bacterium
– There is no animal model of infection with that
particular bacteria.
– A harmless bacteria may cause disease if:
• It has acquired extra virulence factors making it pathogenic.
• It gains access to deep tissues via trauma, surgery, an IV line
• It infects an immuno-compromised patient.
• Not all people infected by a bacteria may develop disease-
subclinical infection is usually more common than clinically
obvious infection."

30. Miasma theory
• The miasma theory of disease transmission held
that diseases such as cholera, chlamydia or the
Black Death were caused by a miasma ancient
Greek: "pollution"), a noxious form of "bad air".
The theory held that the origin of these epidemic
diseases was a miasma, emanating from rotting
organic matter.
• Miasma was considered to be a poisonous vapor
or mist filled with particles from decomposed
matter (miasmata) that caused illnesses.

31. Miasma theory cont..
• The miasmatic position was that diseases were the product of
environmental factors such as
– contaminated water
– foul air
– and poor hygienic conditions.
– Such infection was not passed between individuals but
would affect individuals within the locale that gave rise to
such vapors.
– It was identifiable by its foul smell.
• Predominant theory of disease transmission before the germ
theory of disease took hold in the 19th century.

33. Microbial Flora of the Human
Body

34. Normal Microbial Flora
• 1. Resident Flora
– Microbes that are always present
• 2. Transient Flora
– Microbes that live in or on your body for a period
of time (hours, days, weeks, months) then move on
or die off

35. Symbiotic Relationship
• 1. Mutualistic
– Both organisms benefit – “mutually benefical”
• 2. Commensalistic
– One organism benefits, the other is neither helped
nor harmed
• 3. Opportunistic
– Under normal conditions, microbe does not cause
disease, but if conditions become conducive , it
can cause disease

36. Mutualistic
• Escherichia coli
– Synthesizes Vitamin K & B complex Vitamins
– In return, we provide a warm, moist nutrient rich
environment for E. coli

37. Commensalistic
• We have no Commensalistic relationships with
Bacteria
• If Bacteria are in or on our body, they are either
helping us (Microbial Antagonism) or harming
us.

38. Opportunistic
• Escherichia coli - normally in our digestive
tract where it causes no problems, but if it
gets into the urinary tract it can become
pathogenic.
• Staphylococcus aureus – commonly found in
the upper respiratory tract, but if it gets into a
wound or a burn it can become pathogenic

39. Host-pathogen
Interactions

40. Ecological relationships
Microbial Interactions
Host-Parasite Interactions
Environment

41. PATHOGEN ENVIRONMENT
HOST
DISEASE
TRIAD
OTHER MICROBES
Microbial Interactions

42. Ecological relationships
Symbiosis: Neutral, antagonistic or synergistic
relationship between two dissimilar organisms
(Symbiotes, symbionts) living in close association with
each other;
Mutualism: mutually beneficial relationship between
two species
Commensalism: relationship between two species in
which one is benefited and the other is not affected,
neither negatively nor positively
Parasitism: relationship between two species in which
one benefits (parasite) from the other (host); usually
involves detriment to the host

43. Basic ecological definitions
Flora; microbiota (Microbiology Definition):
Microorganisms present in or characteristic of a special
location (Flora generically refers to plants; Fauna
generically refers to animals)
Indigenous (resident) Microbiota: Microbial flora
typically occupying a particular niche; given diversity of
environmental conditions, organisms tend to segregate
Transient flora: Microbial flora only temporarily
occupying a given niche
Niche (ecological niche): The place of an organism within
its community (ecosystem); unique position occupied by a
particular species, perceived in terms of actual physical
space occupied & function performed within ecosystem

44. Natural microbial habitats
Soil
Water
Air
Animals and Animal Products
Plant and Plant Products

45. Microbial flora of the normal human
body (normal flora)
1. Skin
2. Respiratory tract
Nose and Nasopharynx; Mouth and Oropharynx
3. Eye (Conjunctivae) and Outer ear
4. Intestinal tract
Stomach and Small Intestine; Large Intestine;
Intestinal Tract of Newborn
Antibiotic Alteration of Flora
Significance of Intestinal Flora
5. Genitourinary tract
External Genitalia & Anterior Urethra
Vagina

46. Normally sterile sites in the human
body
Colonization of one of these sites generally involves a defect
or breach in the natural defenses that creates a portal of entry
Brain; Central nervous system
Blood; Tissues; Organ systems
Sinuses; Inner and Middle Ear
Lower Respiratory Tract: Larynx; Trachea;
Bronchioles (bronchi); Lungs; Alveoli
Kidneys; Ureters; Urinary Bladder; Posterior Urethra
Uterus; Endometrium (Inner mucous membrane of
uterus ); Fallopian Tubes; Cervix and Endocervix

47. Factors controlling growth of
microorganisms
1. Nutrient availability: the accessibility of a necessary
resource, substance or compound providing nourishment
to maintain life, i.e. capable of conversion to energy and
structural building blocks
Versatile organisms: Use any organic compounds as
of C and enrgy (sugars, acids. Alcohols e.t.c.)
Fastidious: an organism that has complex nutritional
or cultural requirements, making isolation and culture
more difficult
Major essential elements:
C, O, H, N, S, P, K, Mg, Ca, Fe, Na, Cl
Minor essential elements:

48. 2. Physico/environmental
parameters:
• Water activity/ osmotic pressure (aw)
• Water activity (aw) represents the available water
• Osmotic pressure (p): expressed in atmospheres; reflects
the concentration of solute in an aqueous solution

49. Physico/environmental
parameters cont..
–Oxygen: metabolic oxygen
requirements;
• Obligate aerobe (require free
oxygen)
• Facultative (both aerobic/anaerobic)
• Anaerobic (absence of oxygen)
• Microaerophilic (trace oxygen&
increased carbondioxide)

50. Physico/environmental
parameters cont..
–pH: power of hydrogen; a
measurement of the amount of
hydrogen ion in solution; the
logarithm of the reciprocal of the
hydrogen ion concentration in an
aqueous solution used to express
its acidity or alkalinity (0-14)

51. Physico/environmental
parameters cont..
– Temperature:
• Psycrophile (psychrophilic): cold
temperatures; Optimal growth at 15o to
20oC
• Mesophile (mesophilic): moderate
temperatures; Optimal growth at 20o to
45oC
• Thermophile (thermophilic): elevated
temperatures; Optimal growth at 50o to
70oC

52. Factors controlling growth of
organisms (cont.):
3. Competition: the simultaneous
demand by two or more organisms or
species for a necessary, common resource
or physical space that is in limited or
potentially limited supply, resulting in a
struggle for survival
4. Host immune system: the
cells and tissues involved in recognizing and
attacking foreign substances in the body

54. Acquiring infectious agents
Portal of entry/exit
Ingestion
Inhalation
Direct penetration
Trauma or Surgical Procedure
Needlestick
Arthropod Bite
Sexual Transmission
Transplacental

55. Colonization: the successful occupation of a new habitat
by a species not normally found in this niche
Adherence (attachment): close association of
bacterial cells and host cells generally characterized by
receptors on target sites
Adhesin: structure or macromolecule located on the
surface of a cell or extracellularly that facilitates
adherence of a cell to a surface or to another cell; site
of attachment is often a specific receptor and host cell
receptors are often sugar moieties (lectin), but the
adherence may also be nonspecific
Acquiring infectious agents (cont.)

56. Acquiring infectious agents (cont.)
Invasion: the entry and spread throughout the cells and/or
tissues of the host; specific recognition of receptor sites on
target cells enhances pathogenic advantage
Invasins (invasive factors): structures or
macromolecules that facilitate invasion by a pathogenic
microorganism
Multiplication: the ability of a microorganism to reproduce
during an infection; influenced by underlying disease,
immunologic status, antibiotic treatment, nutrient availability

57. Transmission of disease
Entrance, colonization, penetration: Dependent upon
Age, Sex, Nutrition, Immunologic State and General Health of
Host, and Bacterial Virulence Factors
Vector: a carrier, especially the animal that transfers an
infectious agent from one host to another, usually an
Arthropod
Carrier (Carrier State): symptomless individual who is
host to a pathogenic microorganim with the potential to pass
the pathogen to others
Nosocomial infections: an infection acquired in a
hospital setting that was not present in the host prior to
admission, generally occurring within 72 hours of admission

58. NOSOCOMIAL INFECTIONS in
ACUTE CARE INSTITUTIONS
Infection
Site
Percentage of All
Nosocomial
Infections
Most Common Agents
Urinary
Tract
40%
Escherichia coli, Enterococcus,
Proteus, Klebsiella,
Pseudomonas aeruginosa
Surgical
Wound
20% Staphylococcus aureus,
Staphylococcus epidermidis, E. coli
Pulmonary 10% Klebsiella, Pseudomonas,
E. coli, S. aureus
Primary
Bacteremia
5% - 10% S. aureus, S. epidermidis,
Gram-negative rods
Others 20% - 25% S. aureus, E. coli

59. Epidemiology
Epidemic: Disease occuring suddenly in numbers clearly
in access of normal expectancy
Endemic: Disease present or usually prevalent in a
population or geographic area at all times
Pandemic: A widespread epidemic distributed or occuring
widely throughout a region, country, continent, or globally

60. Tuberculosis SARS* Venezuelan Equine Encephalitis
Hepatitis C AIDS Enterohemorrhagic E. Coli
Malaria Lassa Fever S.American Hemorrhagic Fevers
Influenza Hantavirus Pulmonary Syndrome
Lyme Disease West Nile Fever/Encephalitis*
Emerging Infectious Diseases
 New diseases and diseases with increasing incidences
are called emerging infectious diseases (EIDs).
 EIDs can result from the use of antibiotics and
pesticides, climatic changes, travel, the lack of
vaccination, and insufficient case reporting.
 The CDC, NIH, and WHO are responsible for surveillance
and responses to emerging infectious diseases.

61. Pathogenicity vs. Virulence
Pathogenicity: the quality of producing disease or the
ability to produce pathologic changes or disease
Virulence: a measure of pathogenicity; a measurement of
the degree of disease-producing ability of a microorganism as
indicated by the severity of the disease produced; commonly
ascertained by measuring the dosage required to caused a
specific degree of pathogenicity; one general standard is the
LD50 (lethal dose 50%)

62. PATHOGENICITY vs. Virulence
(Definitons)
Dosage: the number of pathogenic microorganisms
entering the host
LD50 = the number of microorganisms required to cause
lethality (death) in 50% of the test host
True pathogen: any microorganism capable of causing
disease; an infecting agent
Opportunistic pathogen: a usually harmless
microorganism that becomes pathogenic under favorable
conditions causing an opportunistic infection

63. INFECTION vs. Disease
Infection: the colonization and/or invasion and
multiplication of pathogenic microrganisms in the host
with or without the manifestation of disease
Disease: an abnormal condition of body function(s)
or structure that is considered to be harmful to the affected
individual (host); any deviation from or interruption of the
normal structure or function of any part, organ, or system
of the body

64. INFECTION vs. Disease
(Definitons)
Benign: a non-life or non-health threating condition
Malignant: a disease tending to become progressively
worse (Morbidity = illness) and potentially result in death
(Mortality = death)
Contagious: capable of being transmitted from one host
to another; communicable; infectious
Infectious dose: number of pathogenic organisms
required to cause disease in a given host

65. Koch's postulates
Four criteria that were established by Robert Koch to
identify the causative agent of a particular disease,
these include:
1. the microorganism (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 same 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

66. Bacterial Virulence Mechanisms
Adherence (Colonization)
Invasion
Degradative enzymes
Exotoxins
Endotoxin
Induction of excess inflammation
Evasion of phagocytic & immune clearance
Byproducts of growth (gas, acid)
Superantigen
Resistance to antibiotics

67. Microbial pathogenicity
Virulence factors
Colonization factors: specific recognition of receptor sites
on target cells enhances pathogenic advantage
1. Capsule: nonspecific attachment
2. Surface receptors/target sites: Receptors on
both bacteria (adhesins) and host (target)
Examples include:
i) fimbriae (formerly known as pili) of Enterobacteriaceae
ii) Chlamydia binds host N-acetyl-D-glucosamine which is a
cell surface lectin (polysaccharide target receptor)
iii) Protein adhesin of Mycoplasma located in specialized
tip structure; adheres to sialic acid-containing cell receptors

68. MICROBIAL
PATHOGEN ADHESIN RECEPTOR
Staphylococcus aureus L
Li
ip
po
ot
te
ei
ic
ch
ho
oi
ic
c a
ac
ci
id
d Unknown
Staphylococcus spp. S
Sl
li
im
me
e l
la
ay
ye
er
r Unknown
Group A Streptococcus L
LT
TA
A-
-M
M p
pr
ro
ot
te
ei
in
n c
co
om
mp
pl
le
ex
x F
Fi
ib
br
ro
on
ne
ec
ct
ti
in
n
Streptococcus pneumoniae Protein N-acetylhexosamine-gal
Escherichia coli Type 1 f
fi
im
mb
br
ri
ia
ae
e
CFA 1 fimbriae
P fimbriae
D-M
Ma
an
nn
no
os
se
e
GM g
ga
an
ng
gl
li
io
os
si
id
de
e
P blood grp glycolipid
Other Enterobacteriaceae Type 1 fimbriae D-Mannose
Neisseria gonorrhoeae Fimbriae GD1 ganglioside
Treponema pallidum P1, P2, P3 Fibronectin
Chlamydia spp. Cell surface lectin N-acetylglucosamine
Mycoplasma pneumoniae Protein P1 Sialic acid
Vibrio cholerae Type 4 pili Fucose and mannose

69. VIRULENCE FACTORS (cont.)
Invasive factors (invasins): Enable a pathogenic
microorganism to enter and spread throughout the tissues of
the host body; specific recognition of receptor sites on target
cells enhances pathogenic advantage
Degradative enzymes: A class of protein capable of
catalytic reactions; bacterial and host enzymes both play roles
in the disease process

70. Virulence factors (cont.)
Toxigenicity: the ability of a microorganism to cause
disease as determined by the toxin it produces which partly
determines its virulence
1. Endotoxin: a complex bacterial toxin that is
composed of protein, lipid, and polysaccharide (LPS)
which is released only upon lysis of the cell
2. Exotoxins: a potent toxic substance formed
and secreted by species of certain bacteria

71. BASIC EFFECTS of ENDOTOXIN
FEVER: any elevation of body temperature above normal
LEUKOPENIA/LEUKOCYTOSIS: abnormal reduction in number of leukocytes in
blood, (<5000/mm3) / abnormally large number of leukocytes in blood, as during
hemorrhage, infection, inflammation, or fever (>12,000mm3)
METABOLIC EFFECTS : pathogenic organisms can affect any of the body
systems with disruptions in metabolic processes, e.g.,hypotension, hypoglycemia, etc.
RELEASE OF LYMPHOCYTE FACTORS: agranular leukocyte concentrated in
lymphoid tissue; active in immunological responses, including production of antibodies
CELLULAR DEATH:
SEPTIC SHOCK: associated with overwhelming infection resulting in vascular
system failure with sequestration of large volumes of blood in capillaries and veins;
activation of the complement and kinin systems and the release of histamines,
prostaglandins, and other mediators may be involved
DISSEMINATED INTRAVASCULAR COAGULATION (DIC): disorder
characterized by a reduction in the elements involved in blood coagulation due to
their utilization in widespread blood clotting within the vessels; late stages marked
by profuse hemorrhaging
ORGAN NECROSIS: the sum of morphological changes indicative of cell death
and caused by the progressive degradative action of enzymes

72. EXOTOXINS
TWO-COMPONENT (BIPARTITE) A-B TOXINS
with INTRACELLULAR TARGETS: conform to general
structural model; usually one component is a binding
domain (B subunit) associated with absorption to target cell
surface and transfer of active component across cell
membrane, the second component is an enzymatic or
active domain (A subunit) that enzymatically disrupts cell
function
BACTERIAL CYTOLYSINS (a.k.a. Cytotoxins)
with CELL MEMBRANE TARGETS: hemolysis, tissue
necrosis, may be lethal when administered intravenously

73. EXAMPLES of BIPARTITE A-B TOXINS
with
INTRACELLULAR TARGETS
 Diphtheria toxin - ADP-ribosylation inhibits cell protein synthesis by
catalyzing transfer of ADP- ribose from NAD (nicotinimamide adenine
nucleotide) to EF-2 (elongation factor- 2)
 Pseudomonas aeruginosa toxin - similar action as DT
 Cholera toxin - A-subunit catalyzes ADP-ribosylation of the B-subunit
of the stimulatory guanine nucleotide protein Gs; profound life-threatening
diarrhea with profuse outpouring of fluids and electrolytes
 Enterotoxigenic Escherichia coli (ETEC) heat-labile
enterotoxin - similar or identical to cholera toxin
 Tetanus neurotoxin - less well understood; binding domain binds to
neuroreceptor gangliosides, releases inhibitory impulses with trismus
 Botulinum neurotoxin - among most potent of all biological toxins;
binding domain binds to neuroreceptor gangliosides, inhibits release of
acetylcholine at myoneural junction resulting in fatal paralysis

74. BACTERIAL CYTOLYSINS
with
CELL MEMBRANE TARGETS
Three Major Types:
1. Hydrolyze membrane phospholipids (phospholipases);
e.g., Clostridium, Staphylococcus
2. Thiol-activated cytolysins (oxygen-labile) alter membrane
permeability by binding to cholesterol; e.g., Streptococcus,
Clostridium
3. Detergent-like activity on cell membranes; e.g.,
Staphylococcus, rapid rate of lysis

75. ENDOTOXINS
1.I
In
nt
te
eg
gr
ra
al
l p
pa
ar
rt
t o
of
f c
ce
el
ll
l w
wa
al
ll
l
2.Endotoxin is L
LP
PS
S;
lipid A is toxic
3.Heat stable
4.Antigenic; questionable
immunogenicity
5.Toxoids not be produced
6.Many effects on host
7.Produced o
on
nl
ly
y b
by
y g
gr
ra
am
m-
-
n
ne
eg
ga
at
ti
iv
ve
e organisms
EXOTOXINS
1.R
Re
el
le
ea
as
se
ed
d f
fr
ro
om
m t
th
he
e c
ce
el
ll
l
before or after lysis
2.P
Pr
ro
ot
te
ei
in
n
3.Heat labile
4.Antigenic and i
im
mm
mu
un
no
og
ge
en
ni
ic
c
5.T
To
ox
xo
oi
id
ds
s can be produced
6.Specific in effect on host
7.Produced by gram-positive
& gram-negative organisms

76. MICROBIAL PATHOGENICITY (cont.)
RESISTANCE TO HOST DEFENSES
ENCAPSULATION and
ANTIGENIC MIMICRY, MASKING or SHIFT
CAPSULE, GLYCOCALYX or SLIME LAYER
Polysachharide capsules Streptococcus pneumoniae,
Neisseria meningitidis, Haemophilus influenzae, etc.
Polypeptide capsule of Bacillus anthracis
EVASION or INCAPACITATION of PHAGOCYTOSIS
and/or IMMUNE CLEARANCE
PHAGOCYTOSIS INHIBITORS: mechanisms enabling an
invading microorganism to resist being engulfed, ingested,
and or lysed by phagocytes/ phagolysosomes
RESISTANCE to HUMORAL FACTORS
RESISTANCE to CELLULAR FACTORS

77. MICROBIAL PATHOGENICITY (cont.)
DAMAGE TO HOST
DIRECT DAMAGE
(Tissue Damage from Disease Process):
Toxins
Enzymes
INDIRECT DAMAGE
(Tissue Reactions from Immunopathological Response):
Damage Resulting from Vigorous Host Immune Response
(a.k.a, immunopathogenesis; autoimmune
hypersensitivy)
Hypersensitivity Reactions (Types I - IV)

78. HOST RESISTANCE
The degree to which a host can limit the effects of an
infection, ranging from:
 TOLERANCE in which symptoms are suppressed or
unusually large doses of a drug, toxin, or protein are able to be
endured
 HYPERSENSITIVITY in which only a few cells
surrounding the infected cell(s) are affected or an increased
susceptibility to an antigen, such as an allergic reaction to a
previous exposure to an antigen, the extreme case being
anaphylactic shock
 IMMUNITY in which the microorganisms do not multiply
due to any one or a combination of host immune factors or the
biological condition by which a body is capable of resisting or
overcoming an infection or disease

79. HYPERSENSITIVITY REACTIONS
TYPE I: ANAPHYLACTIC REACTION
(ANAPHYLAXIS, ANAPHYLACTIC SHOCK): a life-
threatening immediate hypersensitivity reaction to a previously
encountered antigen, characterized by respiratory distress,
vascular collapse, and shock; allergy or atopic diseases
TYPE II: CYTOTOXIC REACTION: a specific
destructive action against certain cells by an invading agent;
humorally mediated, autoimmune diseases, cytotoxic
diseases, antibody diseases
TYPE III: IMMUNE COMPLEX REACTION: serum
sickness diseases
TYPE IV: CELL-MEDIATED IMMUNE RESPONSE:
delayed-type hypersensitivity, cell- mediated cytotoxic
diseases, granulomatous diseases

80. IMMUNOPATHOLOGICAL RESPONSE
with TISSUE REACTIONS
Type I Hypersensitivity Reactions:
Anaphylactic Reaction (Anaphylaxis;
Anaphylactic shock)
IgE-mediated: Cross-linking of cell-bound IgE
antibodies by antigen with degranulation of mast
cells or basophils
Life-threatening immediate hypersensitivity
reaction to a previously encountered antigen,
characterized by respiratory distress, vascular
collapse, and shock
Allergy or atopic diseases
Atopy: hereditary hypersensitivity to common
environmental antigens

81. IMMUNOPATHOLOGICAL RESPONSE
with TISSUE REACTIONS
Type II Hypersensitivity Reactions:
Humorally-Mediated Autoimmune Diseases
Interaction of cross-reactive antibody with host cell surface antigen;
Autoantibodies and immune complexes
Cytotoxic reaction (antibody-mediated) (ADCC): Specific destructive
action against certain cells presenting antigens from an invading agent

82. IMMUNOPATHOLOGICAL RESPONSE
with TISSUE REACTIONS
Type III Hypersensitivity Reactions:
Immune Complex Reaction
Antibody-mediated
Deposition of circulating immune complexes in
small vessels with complement activation causing
damage to vessels
Serum sickness diseases

83. IMMUNOPATHOLOGICAL RESPONSE
with TISSUE REACTIONS
Type IV Hypersensitivity Reactions:
Cell-Mediated Immune Response
T cells sensitized to “self” antigens secrete
lymphokines that either do direct damage to host cells
(e.g., TNF) or indirect damage enhancing the
inflammatory response
Delayed-type hypersensitivity (TB test) (CD4+
mediated)
Cell-mediated cytotoxic diseases (CD8+ mediated)
Granulomatous disease

84. HOST DEFENSE MECHANISMS
EXTERNAL (PRIMARY): Physical barrier of gross
surface area; e.g., skin, respiratory tract, gastrointestinal
tract, genitourinary tract
Mechanical and Physical Factors: sweat, fatty acids,
pH, indigenous competitive flora (microbial
antagonism), peristalsis, hair, cilia, urinary flushing,
mucus, [tears, nasal secretions, saliva (lysozyme)],
semen (spermine), mucosal secretory antibody (IgA
predominant)

85. HOST DEFENSE MECHANISMS (cont.)
INTERNAL (SECONDARY): When an infecting parasite
succeeds in penetrating the skin or mucuos membranes,
cellular defense mechanisms include local macrophages and
blood-borne phagocytic cells. Mononuclear phagocytes
(monocytes and macrophages) and polymorphonuclear
leukocytes (PMNs) are the most important phagocytic cells
targeting bacterial infections.
MONONUCLEAR PHAGOCYTE SYSTEM (formerly
Reticular Endothelial System): total pool of monocytes
and cells derived from monocytes; predominantly
macrophages (phagocytic cells)

86. HOST DEFENSE MECHANISMS (cont.)
OTHER:
NON-SPECIFIC: oxygen metabolites (superoxide anion
radical, hydrogen peroxide, hydroxyl radicals, halide
radicals), kinin forming system related to clotting
HOST-GENERATED PROTEINS: complex array of
humoral and cellular mediators; e.g., lysosomal
enzymes, lipid mediators, prostaglandins, histamine, heat-
shock proteins (stress proteins)

87. HOST DEFENSE MECHANISMS (cont.)
CELLULAR IMMUNE RESPONSE: any immune
response directed at the cellular level; includes
INFLAMMATION and PHAGOCYTOSIS processes
INFLAMMATORY RESPONSE: a protective
response of tissues affected by disease or injury
characterized by redness, localized heat, swelling, pain,
and possibly impaired function of the infected part
PHAGOCYTOSIS: the process by which certain
phagocytes can ingest extracellular particles by
engulfing them; particles OPSONIZED with antibody are
more rapidly and efficiently ingested
T-LYMPHOCYTES and CYTOKINES

88. HOST DEFENSE MECHANISMS (cont.)
HUMORAL IMMUNE RESPONSE: the sum total of
components of the immune response circulating in the blood
or body fluids ; includes ANTIBODY and COMPLEMENT
systems
COMPLEMENT PROTECTIVE SYSTEM: a protein
system in serum that combines with antibodies to form a
defense against cellular antigens
B-LYMPHOCYTES and
ANTIBODY PRODUCTION: a class of proteins
produced as a result of the introduction of an antigen that
has the ability to combine with the antigen that caused its
production

92. REVIEW

93. PATHOGEN ENVIRONMENT
HOST
DISEASE
TRIAD
OTHER MICROBES
Microbial Interactions
REVIEW

94. ACQUIRING INFECTIOUS AGENTS
PORTAL OF ENTRY/EXIT
INGESTION
INHALATION
DIRECT PENETRATION
Trauma or Surgical Procedure
Needlestick
Arthropod Bite
Sexual Transmission
Transplacental
REVIEW

95. PATHOGENICITY vs. VIRULENCE
PATHOGENICITY: the quality of producing disease or the
ability to produce pathologic changes or disease
VIRULENCE: a measure of pathogenicity; a measurement
of the degree of disease-producing ability of a microorganism
as indicated by the severity of the disease produced;
commonly ascertained by measuring the dosage required to
caused a specific degree of pathogenicity; one general
standard is the LD50 (lethal dose 50%)
REVIEW

96. INFECTION vs. DISEASE
INFECTION: the colonization and/or invasion and
multiplication of pathogenic microrganisms in the host
with or without the manifestation of disease
DISEASE: an abnormal condition of body function(s)
or structure that is considered to be harmful to the affected
individual (host); any deviation from or interruption of the
normal structure or function of any part, organ, or system
of the body
REVIEW

97. KOCH'S POSTULATES
Four criteria that were established by Robert Koch to
identify the causative agent of a particular disease,
these include:
1. the microorganism (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 same 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 REVIEW

98. Bacterial Virulence Mechanisms
Adherence (Colonization)
Invasion
Degradative enzymes
Exotoxins
Endotoxin
Induction of excess inflammation
Evasion of phagocytic & immune clearance
Byproducts of growth (gas, acid)
Superantigen
Resistance to antibiotics
REVIEW

99. BASIC EFFECTS of ENDOTOXIN
FEVER: any elevation of body temperature above normal
LEUKOPENIA/LEUKOCYTOSIS: abnormal reduction in number of leukocytes in
blood, (<5000/mm3) / abnormally large number of leukocytes in blood, as during
hemorrhage, infection, inflammation, or fever (>12,000mm3)
METABOLIC EFFECTS : pathogenic organisms can affect any of the body
systems with disruptions in metabolic processes, e.g.,hypotension, hypoglycemia, etc.
RELEASE OF LYMPHOCYTE FACTORS: agranular leukocyte concentrated in
lymphoid tissue; active in immunological responses, including production of antibodies
CELLULAR DEATH:
SEPTIC SHOCK: associated with overwhelming infection resulting in vascular
system failure with sequestration of large volumes of blood in capillaries and veins;
activation of the complement and kinin systems and the release of histamines,
prostaglandins, and other mediators may be involved
DISSEMINATED INTRAVASCULAR COAGULATION (DIC): disorder
characterized by a reduction in the elements involved in blood coagulation due to
their utilization in widespread blood clotting within the vessels; late stages marked
by profuse hemorrhaging
ORGAN NECROSIS: the sum of morphological changes indicative of cell death
and caused by the progressive degradative action of enzymes REVIEW

100. EXOTOXINS
TWO-COMPONENT (BIPARTITE) A-B TOXINS
with INTRACELLULAR TARGETS: conform to general
structural model; usually one component is a binding
domain (B subunit) associated with absorption to target cell
surface and transfer of active component across cell
membrane, the second component is an enzymatic or
active domain (A subunit) that enzymatically disrupts cell
function
BACTERIAL CYTOLYSINS (a.k.a. Cytotoxins)
with CELL MEMBRANE TARGETS: hemolysis, tissue
necrosis, may be lethal when administered intravenously
REVIEW

101. BACTERIAL CYTOLYSINS
with
CELL MEMBRANE TARGETS
Three Major Types:
1. Hydrolyze membrane phospholipids (phospholipases);
e.g., Clostridium, Staphylococcus
2. Thiol-activated cytolysins (oxygen-labile) alter membrane
permeability by binding to cholesterol; e.g., Streptococcus,
Clostridium
3. Detergent-like activity on cell membranes; e.g.,
Staphylococcus, rapid rate of lysis
REVIEW

102. ENDOTOXINS
1.I
In
nt
te
eg
gr
ra
al
l p
pa
ar
rt
t o
of
f c
ce
el
ll
l w
wa
al
ll
l
2.Endotoxin is L
LP
PS
S;
lipid A is toxic
3.Heat stable
4.Antigenic; questionable
immunogenicity
5.Toxoids not be produced
6.Many effects on host
7.Produced o
on
nl
ly
y b
by
y g
gr
ra
am
m-
-
n
ne
eg
ga
at
ti
iv
ve
e organisms
EXOTOXINS
1.R
Re
el
le
ea
as
se
ed
d f
fr
ro
om
m t
th
he
e c
ce
el
ll
l
before or after lysis
2.P
Pr
ro
ot
te
ei
in
n
3.Heat labile
4.Antigenic and i
im
mm
mu
un
no
og
ge
en
ni
ic
c
5.T
To
ox
xo
oi
id
ds
s can be produced
6.Specific in effect on host
7.Produced by gram-positive
& gram-negative organisms
REVIEW

103. MICROBIAL PATHOGENICITY (cont.)
RESISTANCE TO HOST DEFENSES
ENCAPSULATION and
ANTIGENIC MIMICRY, MASKING or SHIFT
CAPSULE, GLYCOCALYX or SLIME LAYER
Polysachharide capsules Streptococcus pneumoniae,
Neisseria meningitidis, Haemophilus influenzae, etc.
Polypeptide capsule of Bacillus anthracis
EVASION or INCAPACITATION of PHAGOCYTOSIS
and/or IMMUNE CLEARANCE
PHAGOCYTOSIS INHIBITORS: mechanisms enabling an
invading microorganism to resist being engulfed, ingested,
and or lysed by phagocytes/ phagolysosomes
RESISTANCE to HUMORAL FACTORS
RESISTANCE to CELLULAR FACTORS REVIEW

104. MICROBIAL PATHOGENICITY (cont.)
DAMAGE TO HOST
DIRECT DAMAGE
(Tissue Damage from Disease Process):
Toxins
Enzymes
INDIRECT DAMAGE
(Tissue Reactions from Immunopathological Response):
Damage Resulting from Vigorous Host Immune Response
(a.k.a, immunopathogenesis; autoimmune
hypersensitivy)
Hypersensitivity Reactions (Types I - IV)
REVIEW

105. HYPERSENSITIVITY REACTIONS
TYPE I: ANAPHYLACTIC REACTION
(ANAPHYLAXIS, ANAPHYLACTIC SHOCK): a life-
threatening immediate hypersensitivity reaction to a previously
encountered antigen, characterized by respiratory distress,
vascular collapse, and shock; allergy or atopic diseases
TYPE II: CYTOTOXIC REACTION: a specific
destructive action against certain cells by an invading agent;
humorally mediated, autoimmune diseases, cytotoxic
diseases, antibody diseases
TYPE III: IMMUNE COMPLEX REACTION: serum
sickness diseases
TYPE IV: CELL-MEDIATED IMMUNE RESPONSE:
delayed-type hypersensitivity, cell- mediated cytotoxic
diseases, granulomatous diseases REVIEW

106. HOST DEFENSE MECHANISMS (cont.)
CELLULAR IMMUNE RESPONSE: any immune
response directed at the cellular level; includes
INFLAMMATION and PHAGOCYTOSIS processes
INFLAMMATORY RESPONSE: a protective
response of tissues affected by disease or injury
characterized by redness, localized heat, swelling, pain,
and possibly impaired function of the infected part
PHAGOCYTOSIS: the process by which certain
phagocytes can ingest extracellular particles by
engulfing them; particles OPSONIZED with antibody are
more rapidly and efficiently ingested
T-LYMPHOCYTES and CYTOKINES
REVIEW

107. HOST DEFENSE MECHANISMS (cont.)
HUMORAL IMMUNE RESPONSE: the sum total of
components of the immune response circulating in the blood
or body fluids ; includes ANTIBODY and COMPLEMENT
systems
COMPLEMENT PROTECTIVE SYSTEM: a protein
system in serum that combines with antibodies to form a
defense against cellular antigens
B-LYMPHOCYTES and
ANTIBODY PRODUCTION: a class of proteins
produced as a result of the introduction of an antigen that
has the ability to combine with the antigen that caused its
production
REVIEW