Download Question bank- 5.bacterial virulence: Q1 Explain briefly the following

Question bank- 5.bacterial virulence:
Q1 Explain briefly the following :
a. Bacterial classification according to their virulence .
1. Virulent(‫)ضارية‬.
2. A virulent )‫(غير ضارية‬.
b. Disease production depends on two factors
1. Virulence of microorganism(‫)الضراوة‬.
2. The resistance of invaded subject (host).
c . Bacterial component of virulent state are:
1.Toxigenicity(‫)القدرة على أنتاج السموم‬:
of the microorganism means the ability of microbe to produce a toxin.
2. Invasiveness (‫)القدرة على الغزو‬:
The ability of microorganism to invade and multiply into tissues, aggressive
substances which the micro produces enters the body to assist the microbes to
overcome the defenses
of the body.
3. Nature and physiology :
The capsulated microorganism is highly virulent than non-capsulated because the
capsulate protects the microbes against the body.
4. Route and dose of infection :
The route is assisting the microbes to enter to the body also the dose determines the
occurrence of infection.
d. Methods used to Measurement of bacterial virulence:
We measure the virulence by:
1. Minimum lethal dose (MLD).
2. Lethal dose 50(LD50).
1. Minimum lethal dose:
It means the number of microorganism or the low number of micro which
kills the test animals in a specific period.
2. LD50:
Number of micro which kills 50% of test animal.
e. Kocks postulate ( routes):
1. The organism must be isolated from every case of disease
2. The organism must be isolated in pure cultures in vitro.
3. Organism must be producing the disease when injected in to laboratory animals.
4. The organism must be isolated from the laboratory animals .Tubercle bacilli
cause T.b. Tubercle bacilli isolate from 100 cases for ex: then injected in to lab
animals so T.b lesion occurs, isolated of tubercle bacilli from the infected lab animal.
f. Define the following :
1. Infection: growth and multiplication of a microbe in or on the body with or
without the production of disease.
2. The capacity of a bacterium to cause disease reflects its relative
“Pathogenicity.”
3. Virulence is the measure of the pathogenicity of a microorganism.
4. Pathogenesis refers both to the mechanism of infection and to the mechanism
by which disease develops.
5. Pathogenesis of sepsis (septicemia) means bacterial growth and multiplication .
6. Bacteremia introduce of bacteria into blood circulation.
h. Host Susceptibility factor :
1.
Susceptibility to bacterial infections
Virulence
=> Host Defenses vs Bacterial
2. Host Defenses:
- Barriers (skin & mucus) – first line
- Innate Immune Responses (complement, macrophages &
cytokines) – the early stage
- Adaptive Immune Responses (Ag-specific B & T cells) – the
later stage.
5. Opportunistic pathogens are typically members of normal flora and cause diseases
when they are introduced into unprotected sites, usually occur in people with underlying
conditions.
g. The most frequent portals of bacterial entry:
1. Mucus .
2. Skin
Routes:
Ingestion, inhalation, trauma, needles, catheters, arthropod bite, sexual transmission
i.
Characteristics of Pathogenic Bacteria
1. Transmissibility
2. Adherence to host cells
3. Invasion of host cells and tissue
4. Evasion (‫)التهرب‬of the host immune system
5. Toxigenicity
6. Resistance to antibiotic.
m. Adhesion
Adherence of bacterium to epithelial or endothelial cells allow them to colonize the
tissue.
Common adhesins: pili (fimbriae), slime, lipoteichoic acid, surface proteins or
lectins.
n. Biofilm
Biofilm, formed on a surface by the bacteria that are bound together within a sticky web
of polysaccharide, is a special bacterial adaptation that facilitates colonization on the
surgical appliances (e.g., artificial valves or indwelling catheters) and dental plaque. It
can protect the bacteria from host defenses and antibiotics.
o. Lipid A of lipopolysaccharide is responsible for endotoxin activity
Q2 Enuemerate the following :
a. Pathological Mechanisms of Bacterial Infections
1. Bacteria-mediated Pathogenesis
2. Host-mediated Pathogenesis
3. Bacterial virulence factors
=> bacterial factors causing diseases
b. Bacterial Virulence Mechanisms:
c. Microbial defenses against host immunologic clearance.
Encapsulation (Inhibition of phagocytosis and serum
bactericidal effect)
Antigenic mimicry
Antigenic masking
Antigenic or phase variation
Intracellular multiplication
Escape phagosome
Inhibition of phagolysosome fusion
d.
e.
f.
g.
Resistance to lysosomal enzymes
Production of anti-immunoglobulin protease
Inhibition of chemotaxis
Destruction of phagocytes
Regulation of bacterial virulence factors
Environmental factors often control the expression of the virulence genes.
Common factors:
temperature, iron availability, osmolarity, growth phase, pH, specific ions,
specific nutrient factors, bacterial cell-density, interaction with host cells.
m. Bacterial virulence factors
Adhesins
Pili (fimbriae)
Nonfimbrial adhesins
Invasion of host cells
Tissue damage
Growth byproducts
Tissue-degrading enzymes
Immunopathogenesis
Toxins
Exotoxins (cytolytic enzymes
and A-B toxins); enterotoxins;
superantigens;
endotoxin and other cell wall
Antiphagocytic factors
Intracellular survival
Antigenic heterogeneity
Antigenic variation
Phase variation
Iron acquisition
Siderophores
components
Receptors for
iron-containing molecules
Resistance to antibiotics
n.
Regulation of bacterial virulence factors.
Environmental factors often control the expression of the virulence genes.
Common factors:
temperature, iron availability, osmolarity, growth phase, pH, specific ions, specific nutrient
factors, bacterial cell-density, interaction with host cells.
Q2 Explain why the fallowing.
a. A bacterium may cause diseases by?
1. Destroying tissue (invasiveness)
2. Producing toxins (toxigenicity)
3. Stimulating overwhelming host immune responses
b. Mechanisms for escaping phagocytic clearance and intracellular survival?
c.
d.
e.
f.
g.
h.
i.
j.
k.
l.
m.
n.
o.
p.
Exceptions to Koch’s Postulates
Koch’s principles do not apply to all diseases.
1. Some microbes cannot be cultured in artificial media.
Treponema pallidum (syphillis)
Mycobacterium leprae (leprosy)
Ricketsias, chlamydias, and viruses only multiply within cells.
2. One disease may involve several different pathogens.
Diarrhea
Pneumonia
Meningitis
Peritonitis
Nephritis
3. Some pathogens may cause several different diseases.
Streptococcus pyogenes: Scarlet fever, sore throat, skin infections, bone infections,
etc.
q. Mycobacterium tuberculosis: Causes disease of lungs, skin, bones, and internal
organs.
d. Define the following
Symptoms: Subjective feelings not obvious to an observer.
Example: Pain and malaise.
Signs: Objective changes that can be measured.
Example: Fever, redness, swelling, paralysis.
Syndrome: A group of signs and symptoms that are associated with a disease.
Morbidity rate is number of cases of illness divided by population at risk
Mortality rate reflects population that dies from disease
Incidence reflects number of new cases per specific time period
Prevalence reflects total number of existing cases
Diseases that are constantly present are endemic
Unusually large number of cases in a population constitutes an epidemic
When epidemics spread worldwide they are termed pandemic
Outbreak refers to a cluster of cases in a brief time affecting a specific population
Acute Disease: Develops rapidly, but lasts a short time.
Examples: Flu and common cold.
Chronic Disease: Develops more slowly, and reactions are less severe. Tend to recur for
long periods or to be continual.
Examples: Tuberculosis, hepatitis B, and infectious mononucleosis.
Subacute Disease: Intermediate between acute and chronic.
Examples: Subacute bacterial endocarditis (streptococci).
Latent Disease: Causative agent remains inactive for a time, but then
becomes active and produces disease symptoms.
Examples: Shingles, genital and oral herpes, AIDS.
Example: AIDS (Acquired Immune Deficiency Syndrome) is a syndrome that varies
from one individual to another.
e. Classifying Infectious Diseases according to their spreading:
1. Communicable Diseases:
Spread from one host to another, directly or indirectly.
Example: Tuberculosis, herpes, flu, AIDS, chickenpox, mumps, polio, and hepatitis.
2. Contagious Diseases:
Spread easily from one person to another.
Example: Chickenpox and measles.
3. Noncommunicable Diseases:
4. Not spread from one host to another. Caused by microbes that live outside the
body or by opportunistic pathogens that live inside the body.
Example: Tetanus, botulism, and yeast infections.
f. Propability for Exposure to Infectious Agents: