slides

1. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Komar University of Science and
Technology
MICROBIOLOGY I
Dr. Khawaja Shakeel Ahmed
Assistant Professor

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BACTERIAL PATHOGENICITY
Contents
1. Terminlogies (Colonization, Pathogen, Infection, Infectious disease,
Disease, Infectivity, Virulance Virulance factor)
2. Factors influencing the availabilty of microbes any body site
3. Classifying infectious disease
4. Epidemological terms
5. Severity / Duration of a disease
6. Transmission of a disease
7. Nosocomial infections
9. Factors influencing host resistance
10. Stages of bacterial pathogenesis
11. Types of bacterial infection
12. Typical stage of an infectious disease

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BACTERIAL PATHOGENICITY
• Of the thousands of microbial species, ≤ 300 can cause
disease in humans
• Terminologies
• Colonization: Growth of microbe on body surfaces;
no recognizable reaction in the host.
• Pathogen: Microbes capable of causing disease.
• Infection: Colonization of the body by pathogens.
• Infectious disease: infection that results in physical
dysfunction or a lesion - damage
to the host.
• Disease: An abnormal state in which the body is not
functionally normal

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BACTERIAL PATHOGENICITY
• Infectivity - ability of a microorganism to cause
infection.
• Pathogenicity - ability of a microorganism to cause
infectious disease, i.e., pathologic changes.
• Virulence - the degree of pathogenicity of a
microorganism as indicated by its ability to invade and
damage the host.
• Virulence factor - those components of an organisms
that promote its capacity to cause disease but do not
affect its viability, e.g. toxins and surface antigens
[ capsule].

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Factors influencing the availability of
microorganisms at any body site
• Availability or unavailability of oxygen
• The availability of appropriate receptor sites for
attachment
• The pH of the host site (stomach)
• The availability of nutrients
• The influence exerted by other microorganisms
at the site
• The immunological response of the host to the
presence of the microbe

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Classifying Infectious Diseases
• Communicable / Contagious disease
A disease that is easily spread
from one person to other.
• Non-communicable disease
A disease that is not transmitted
from one host to another.

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• Occurrence of Disease can described as:
• Prevalence: Fraction of a population having
a specific disease at a given time.
• Endemic disease: Disease constantly present in a
population at low level in certain
location.
• Epidemic disease: widespread occurrence of disease
in a given area in a particular time.
• Pandemic disease: Worldwide epidemic. i.e. disease
that spread rapidly over large area
of the globe.
Epidemiological Terms

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• Acute disease Symptoms develop rapidly
• Chronic disease Disease develops slowly
• Subacute disease Symptoms between acute and
chronic
• Latent disease Disease with a period of no
symptoms when the patient is
inactive
Severity or Duration of a Disease

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• Bacteremia Bacteria in the blood
• Septicemia Growth of bacteria in the blood
• Toxemia Toxins in the blood
• Viremia Viruses in the blood

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I. Transmission of Disease Between individuals
A. Direct
• Requires close association between infected and
susceptible host.
• Intimate contact (touching) or airborne by droplet
Transmission of Disease

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I. Transmission of Disease between Individuals

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B. Indirect
• Vehicle Transmission by an inanimate reservoir
(food, water)
• Vectors Arthropods, especially fleas, ticks,
and mosquitoes.
• Mechanical Fly carries pathogen on feet
• Biological Pathogen reproduces in vector
Transmission of Disease between Individuals

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Transmission of Disease
Figure 14.6b, c

14. Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 14.7, 9
• Are acquired as a result of a hospital stay
• 5-15% of all hospital patients acquire nosocomial
infections
Nosocomial (Hospital-Acquired) Infections

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II.Transmission of microbes within a species
1. Horizontal spread: person to person by way of direct
contact or contamination of environment.
2. Vertical spread: parents to offspring via placenta or
milk.

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Factors influencing host resistance
1. Immunological state of the host.
2. Nutrition
3. Occupation (determines exposure to pathogens)
4. Underlying conditions, e.g. diabetes, viral infections,
cancer therapy

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Stages of Bacterial Pathogenesis
1. Transmission from an external source into the portal of
entry.
2. Evasion of primary host defenses such as skin.
3. Adherence to mucous membranes.
4. Colonization of the bacteria at the site of adherence.
5. Disease symptoms caused by toxin production or
invasion accompanied by inflammation.
6. Specific and non-specific host responses
7. Progression or resolution of the disease.

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Types of Bacterial Infections
Bacteria cause disease by two major mechanisms:
• Toxin Production
• Invasion and inflammation
1. Toxin Production
Toxins two types:
Exotoxins and Endotoxins

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Toxin Production
A. Exotoxins
• Polypeptides secreted by the bacterial cell into the
surrounding environment without disruption of the
bacterial cell.
• Exotoxins are among the most toxic substances known.
• <1μg of tetanus toxin is lethal
• Exotoxins are secreted by most Gram Positive bacteria
– and some Gram Negatives.
• Exotoxins can be converted to toxoids. (by heat/acid)
• Toxoids are used for vaccine production
• Toxoids retain their antigenicity but have lost their
toxicity.

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Exotoxins
Figure 15.4a

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Toxin Production
B. Endotoxins
Are lipopolysaccharides (LPS) which form the integral
part of the cell wall.
• Produced only by Gram-negative bacteria.
• Released usually when the cell lyses, are not actively
released from the cell.
• Can cause fever and shock, and general symptoms.
• Endotoxins are poorly antigenic, do not induce
antitoxins, and do not form toxoids.

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Endotoxin
Figure 15.4b

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Types of Bacterial Infection
2. Invasion and Inflammation
• Invasive bacteria after being penetrating the skin, they
grow to a large number locally and induce an
inflammatory response consisting of:
• erythema (abnormal redness of the skin),
• edema (swelling )
• pain.
• Inflammation is an important host defense induced by
the presence of bacteria in the body.

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Inflammation
Figure 16.9a, b

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Typical Stage of an Infectious Disease
1. Incubation period, is the time between the
acquirement of the organism (toxin) and the beginning
of symptoms.
2. Prodromal period = non-specific symptoms such as
fever, malaise, and loss of appetite occur.
3. Specific illness period = evident characteristic signs
and symptoms of the disease occur.
4. Recovery period during which the illness declines
and the patient returns to healthy state.

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The Stages of a Disease
Figure 14.5

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The Stages of a Disease
Figure 14.5