chap 5

Question 1

Pathogenicity

Answer 1

is the ability of a pathogen to produce a disease by overcoming the defenses of the host.

Question 2

Virulence

Answer 2

is the degree or extent of pathogenicity.

Question 3

To cause disease an organism must:

Answer 3

Enter into the host
Adhere to tissue within the host
Cause damage to the host in some manner

Question 4

The specific route by which a particular pathogen enters the body.

Answer 4

Skin
Mucous Membranes
The Parenteral Route

Question 5

PORTALS OF ENTRY
I-Skin:
The largest organ of the body. When unbroken, it is an effective barrier for most microorganisms.
Most microorganisms cannot penetrate intact skin

Answer 5

• may gain entrance through openings in the skin
• may enter hair follicles or sweat ducts
• some fungi infect the skin itself.

Question 6

Respiratory Tract:

Answer 6

microorganisms that are inhaled with droplets of moisture and dust particles gain access to the respiratory tract.
Exp of respiratory diseases: Common cold, Flu, Tuberculosis, Whooping cough, Pneumonia, Diphtheria, Measles

Question 7

Microorganisms enter the gastrointestinal tract by ingestion via

Answer 7

contaminated food, water, and contaminated fingers or hands
- Most microbes that enter the G.I. tract are destroyed by HCL & enzymes of stomach or bile & enzymes of small intestine, those that survive cause disease.
Ex: Salmonellosis, Shigellosis, Cholera, Ulcer, Botulism, poliomyelitis, hepatitis A, typhoid fever, amebic dysentery, giardiasis

Question 8

Genitourinary Tract:

Answer 8

portal of entry for pathogens that are contracted sexually. Some microbes that cause sexually transmitted infections (STIs) may penetrate an unbroken mucous membrane. Others require a cut or abrasion of some type.
Examples of STIs are HIV infection, genital warts, chlamydia, herpes: Herpes simplex II, Syphilis-Treponemapallidum, and Gonorrhea-Neisseria gonorrhoeae.

Question 9

Conjunctiva:

Answer 9

delicate membrane that covers the eyeballs and lines the eyelids
Ex: Trachoma :Chlamydia trachomatis

Question 10

Parenteral route:

Answer 10

Some microorganisms can gain access to tissues by direct penetration (inoculation)through the skin and mucous membranes in bites, injections, punctures, scratches, surgery, splitting of skin due to swelling or dryness, and other wounds.
Ex: HIV, the hepatitis viruses,

Question 11

Many organisms can cause infections only when they gain access through their specific portal of entry.

Answer 11

1. Streptococcus pneumoniae
If inhaled can cause pneumonia
If it enters the G.I. Tract, no disease
2. Salmonella typhi
If it enters the G.I. Tract: it can cause Typhoid Fever
if present on the skin »»no disease

Question 12

The virulence of a microbe or its toxin can be expressed by

Answer 12

LD50 & ID50

Question 13

LD50 -

Answer 13

Lethal Dose of a microbes toxin that will kill 50% of the inoculated hosts

Question 14

ID50 -

Answer 14

Infectious dose required to cause disease in 50% of the inoculated hosts

Question 15

Bacillus anthraciscan cause infection via three different portals of entry.

Answer 15

The ID50 through the skin (cutaneous anthrax) is 10 to 50 endospores;
The ID50 for inhalation anthrax is inhalation of 10,000 to 20,000 endospores; and
The ID50 for gastrointestinal anthrax is ingestion of 250,000 to 1,000,000 endospores
b-A study of Vibrio choleraeshowed that the ID50 is 108 cells; but if stomach acid is neutralized with bicarbonate, the number of cells required to cause an infection decreases significantly.

Question 16

Adherence

Answer 16

once entry has been accomplished, most microorganisms have mechanisms of host attachment,
It is a necessary step in pathogenicity.
For bacterial pathogens, successful adherenceis usually a necessary prerequisite for virulence and even infection.
Such microbial structures as glycocalyx and fimbriae (i.e., attachment pili) are involved in adherence.

Question 17

Exp:Streptococcus mutans

Answer 17

a bacterium that plays a role in tooth decay, attaches to the surface of teeth by its glycocalyx: an enzyme, produced by S. mutans, converts glucose into a sticky polysaccharide called dextran which forms the glycocalyx .

Question 18

Other MO Actinomyces have fimbriae that stick on the gycocalyx of S. mutans

Answer 18

.The combination of S. mutans, Actinomyces, and dextran make up dental plaque and contribute to dental caries

Question 19

Biofilms:

Answer 19

Microbes have the ability to come together in masses, cling to surfaces, and take in and share available nutrients. Biofilms are these communities, which constitute masses of microbes and their extracellular products that can attach to living and nonliving surfaces.
Examples of biofilms include the dental plaque on teeth, the algae on the walls of swimming pools, and the scum that accumulates on shower doors.

Question 20

How bacterial pathogens penetrate host defenses?

B. Components of the Cell Wall

Answer 20

Proteins in the cell wall can facilitate adherence or prevent a pathogen from being phagocytized.
M protein of S. pyogenes(cell surface and fimbriae)
However, some microbes can reproduce inside phagocytes.
M. tuberculosis

Question 21

How bacterial pathogens penetrate host defenses?

B. Components of the Cell Wall

Answer 21

Proteins in the cell wall can facilitate adherence or prevent a pathogen from being phagocytized.
M protein of S. pyogenes(cell surface and fimbriae)
However, some microbes can reproduce inside phagocytes.
M. tuberculosis

Question 22

How bacterial pathogens penetrate host defenses?

C. Enzymes

Answer 22

The virulence of some bacteria is thought to be aided by the production of extracellular enzymes (exoenzymes) and related substances. These chemicals can digest materials between cells and form or digest blood clots, among other functions.
1. Leukocidins
Enzymes that are toxic to leukocytes especially exotoxins of pathogenic Staphylococci and Streptococci that destroy leukocytes by lysis.
2. Hemolysins
They cause the destruction of red blood cells-important producer of this enzyme = Clostridium perfringes3. Coagulases are bacterial enzymes that coagulate (clot) the fibrinogen in blood. Fibrinogen, a plasma protein produced by the liver, is converted by coagulases into fibrin, the threads that form a blood clot. The fibrin clot may protect the bacterium from phagocytosis and isolate it from other defenses of the host.
Coagulases are produced by some members of the genus Staphylococcus. However, some staphylococci that do not produce coagulases are still virulent. (Capsules may be more important to their virulence.)

Question 23

Bacterial kinases are

Answer 23

bacterial enzymes that break down fibrin and thus digest clots formed by the body to isolate the infection.
One of the better-known kinases is fibrinolysin (streptokinase), which is produced by streptococci as such as Streptococcus pyogenes.

Question 24

Hyaluronidase

Answer 24

is another enzyme secreted by certain bacteria, such as streptococci, clostridia that cause gas gangrene.
This action is thought to be involved in the tissue blackening of infected wounds and to help the microorganism spread from its initial site of infection.

Question 25

Collagenase,

Answer 25

produced by several species of Clostridium, facilitates the spread of gas gangrene.

Question 26

The production of toxins 2

Answer 26

Toxins transported by blood or lymph can cause serious and sometimes fatal effects; some toxins produce fever, cardiovascular disturbances, diarrhea, and shock.
Some toxins can also inhibit protein synthesis, destroy blood cells and blood vessels and disrupt the nervous system by causing spasms.
Over 220 or so known toxins, only 40 % cause disease by destroying eukaryotic cell membranes
Two types: Endotoxins & Exotoxins

Question 27

How bacterial pathogens damage cells?

Answer 27

A-Using the host’s nutrients
Some pathogens secrete proteins that are able to take nutrients from blood (Ex: iron)
B-Direct damage
Once pathogens attach to host cells, they can cause direct damage as the pathogens use the host cell for nutrients and produce waste products.
As pathogens metabolize and multiply in cells, the cells usually rupture.
Pathogens that rupture cells can spread to other tissues in even greater numbers
Some bacteria can also penetrate host cells by excreting enzymes and by their own motility; such penetration can itself damage the host cell.

C-The production of Toxins
Toxins are poisonous substances that are produced by MO.
The capacity of MO to produce toxins is called toxigenicity
Toxemia: presence of toxins in the blood.

Question 28

antitoxins

Answer 28

antibodies produced against exotoxins

Question 29

Naming exotoxins:

Answer 29

A-The type of host cell that is attacked.
Neurotoxins attack nerve cells,
Cardiotoxinsattack heart cells,
Hepatotoxinsattack liver cells,
Leukotoxinsattack leukocytes,
Enterotoxins attack the lining of the gastrointestinal tract
Cytotoxinsattack a wide variety of cells.
B-The diseases with which they are associated. Examples include:
Diphtheria toxin (cause of diphtheria) and tetanus toxin (cause of
tetanus).
C-The specific bacterium that produces them,
Botulinumtoxin (Clostridium botulinum) and Vibrio enterotoxin (Vibrio cholerae).

Question 30

Cytotoxins include

Answer 30

• diphtheria toxin which inhibits protein synthesis (Corynebacteriumdiphtheriae)

Question 31

Neurotoxins which interfere with normal nerve impulses include

Answer 31

botulinumtoxin: which prevents nerve transmission to muscles and tetanus toxin: which prevents inhibitory nerve transmission.

Question 32

• Erythrogenictoxins, by Streptococcus pyogenes

Answer 32

, which damage capillaries and produce a red skin rash.

Question 33

Enterotoxins which

Answer 33

affect cells coating the G.I. Tract:
Cholerae Enterotoxins (Vibriocholerae) which induce fluid and electrolyte loss from host cells,

Question 34

endotoxins

Answer 34

They are part of the outer portion of the cell wall of Gram negative bacteria ( Lipid A component of the LPS of the cell wall of gram-negative bacteria)
Bacterial cell death, antibiotics, and antibodies may cause the release of endotoxins.
They cause fever and shock
They allow bacteria to cross the blood-brain barrier.
29

Question 35

endotoxins 2

Answer 35

All endotoxins produce the same signs and symptoms although not to the same degree, including chills, fever, weakness in some cases shock and even death
They can activate blood-clotting proteins(clots).

Question 36

Organisms that produce endotoxin include:

Answer 36

Salmonella typhi (the causative agent of typhoid fever),
Proteus spp. (frequently the causative agents of urinary tract infections),
Neisseria meningitidis (the causative agent of meningococcal meningitis).

Question 37

Viruses

Answer 37

Viruses avoid the host’s immune response by growing inside cells.
Viruses gain access to host via attachment sitesfor receptors on the host cell.
Signs of viral infections are called cytopathic effects(CPE).
Some viruses cause cytocidal effects(cell death), and others cause noncytocidal effects.

Question 38

Cytopathic effects

Answer 38

include the stopping of mitosis, lysis, the formation of inclusion bodies, cell fusion, antigenic changes, chromosomal changes, and transformation.

Question 39

Symptoms of fungal infections can be caused by

Answer 39

capsules, toxins, and allergic responses.

Question 40

A biofilm forms when

Answer 40

microbes adhere to a particular surface that is typically moist and contains organic matter.
The first microbes to attach are usually bacteria. Once they adhere to the surface, they multiply and secrete a glycocalyx that further attaches the bacteria to each other and to the surface

Question 41

Symptoms of protozoal and helminthic diseases can be caused by

Answer 41

damage to host tissue or by the metabolic waste products of the parasite.
Some protozoa change their surface antigens while growing in a host so the host’s antibodies don’t kill the protozoa.

Question 42

Some algae

Answer 42

produce neurotoxins that cause paralysis when ingested by humans.