micro ch. 15 pearson

The most frequently used portal of entry for most pathogens is which of the following?

Parenteral route

Skin

Mucous membranes of the respiratory tract

Mucous membranes of the gastrointestinal tract

All of these portals are used equally

Mucous membranes of the respiratory tract

What is the ID50?

The dose that will cause an infection in some of the test population

The dose that will kill some of the test population

The dose that will cause an infection in 50 percent of the test population

The dose that will kill 50 percent of the test population

A measure of pathogenicity

The dose that will cause an infection in 50 percent of the test population

Superantigens produce intense immune responses by stimulating lymphocytes to produce ________.

cytokines

interferons

exotoxins

endotoxins

leukocidins

cytokines

Polio is transmitted by ingestion of water contaminated with feces containing polio virus. What portal of entry does polio virus use?

Parenteral

Mucous membranes

Skin

Skin and parenteral

Skin, parenteral, and mucous membranes

Mucous membranes

Bacterium	Portal of Entry	ID50
Staphylococcus aureus	Wound	<10
Staphylococcus aureus	Wound + Ampicillin	300

the table shows the ID ₅₀ for Staphylococcus aureus in wounds with and without the administration of ampicillin before surgery. Based on the data, the administration of ampicillin before surgery

decreases the risk of staphylococcal infection.

increases the risk of staphylococcal infection.

has no effect on risk of infection.

replaces tetracycline.

The answer cannot be determined based on the information provided.

decreases the risk of staphylococcal infection.

Bacterium	ID50
E. coli O157:H7	20
Legionella pneumophila	1
Shigella	10
Treponema pallidum	57

Which organism in the table most easily causes an infection?

Shigella

Legionella pneumophila

Treponema pallidum

E. coli O157:H7

The answer cannot be determined based on the information provided.

Legionella pneumophila

In mice, the LD50 for staphylococcal enterotoxin is 1350 ng/kg, and the LD50 for Shiga toxin is 250 ng/kg. Which of the following statements is true?

Staphylococcal enterotoxin is the more lethal of the two toxins.

The parenteral route is the preferred portal entry for Shigella bacteria.

Shiga toxin is more lethal than staphylococcal enterotoxin.

More organisms of Staphylococcal bacteria must be ingested to cause infection, as compared to Shigella bacteria.

Shiga toxin is more lethal than staphylococcal enterotoxin.

Which of the following would be an example of an infection initiated via the parenteral route?

An individual contracts gonorrhea as a result of unprotected sex.

An individual contracts a hookworm infection as a result of walking around outside barefoot.

An individual contracts a gastrointestinal infection by consuming contaminated water.

An individual contracts hepatitis B from an accidental stick with a contaminated needle.

An individual contracts hepatitis B from an accidental stick with a contaminated needle.

Biofilms provide pathogens the mechanism that enables them to be resistant to antimicrobial agents.

True

False

true

The ability of some microbes, such as Trypanosoma or Giardia to alter their surface molecules and evade destruction by the host's antibodies is called

cytopathic effect.

antigenic variation.

lysogenic conversion.

cytocidal effect.

virulence.

antigenic variation

Which is not employed by pathogens to avoid destruction by the host phagocytosis?

Possessing ability to replicate within a phagolysosome

Producing superantigens

Possessing ability to remain dormant within a phagocyte

Producing a capsule

Forming biofilms

Producing superantigens

A pathogen that is capable of antigenic variation can ________________.

avoid host immune defenses

cause fever, low blood pressure, and bleeding problems

adhere tightly to host tissues

lyse host cells

avoid host immune defenses

Endotoxins are:

Molecules that bind nerve cells

Associated with gram-positive bacteria

A-B toxins

Excreted from the cell

Derived from the gram-negative cell wall

Derived from the gram-negative cell wall

Which of the following contributes to the virulence of a pathogen?

evasion of host defenses

numbers of microorganisms that gain access to a host and evasion of host defenses

toxin production

numbers of microorganisms that gain access to a host

numbers of microorganisms that gain access to a host, evasion of host defenses, and toxin production

numbers of microorganisms that gain access to a host, evasion of host defenses, and toxin production

Lysogenic bacteriophages contribute to bacterial virulence because bacteriophages

carry plasmids.

kill human cells.

give new gene sequences to the host bacteria.

produce toxins.

kill the bacteria, causing release of endotoxins.

give new gene sequences to the host bacteria.

Twenty-five people developed symptoms of nausea, vomiting, and diarrhea three to six hours after attending a church picnic where they ate a ham and green bean casserole with cream sauce. The most likely cause of this case of food intoxication is

cholera toxin.

botulinum toxin.

erythrogenic toxin.

aflatoxin.

staphylococcal enterotoxin.

staphylococcal enterotoxin.

Gram-negative septic shock results from the following events. What is the second step?

Fever occurs.

Body temperature is reset in the hypothalamus.

LPS is released from gram-negative bacteria.

IL-1 is released.

Phagocytes ingest gram-negative bacteria.

LPS is released from gram-negative bacteria.

Antibiotics can lead to septic shock if used to treat

gram-negative bacterial infections.

gram-positive bacterial infections.

protozoan infections.

helminth infestations.

viral infections.

gram-negative bacterial infections.

A retired contract administrator who enjoyed gardening sought medical attention for what appeared to be a sinus infection. He received antimicrobial treatment, but the condition became worse, and he was experiencing severe painful spasms in his jaw. He admitted to injuring himself with a gardening tool while wearing sandals in the yard but did not seek medical attention for the wound. The man is likely experiencing ________.

meningitis

allergic rhinitis

intoxication caused by a focal C. tetani infection

a septic shock

LPS-mediated inflammatory response

intoxication caused by a focal C. tetani infection

The principle mechanism of the A-B exotoxins is that the A component binds to the host cell receptors to allow the B component to enter the cell.

True

False

False

Symptoms of protozoan and helminthic diseases are due to

tissue damage due to growth of the parasite on the tissues, waste products excreted by the parasite, and products released from damaged tissues.

products released from damaged tissues.

waste products excreted by the parasite.

tissue damage due to growth of the parasite on the tissues and waste products excreted by the parasite.

tissue damage due to growth of the parasite on the tissues.

tissue damage due to growth of the parasite on the tissues, waste products excreted by the parasite, and products released from damaged tissues.

Ergot and aflatoxin are toxins sometimes found in grains contaminated with fungi.

True

False

True