The best description of direct damage by a pathogen is

host cells destroyed when pathogens metabolize and multiply.

Superantigens produce intense immune responses by stimulating lymphocytes to produce

cytokines

Injectable drugs are tested for endotoxins by

the Limulus amoebocyte lysate test.

Which of the following statements about exotoxins is generally FALSE?

They are resistant to heat.Submit

Which of the following statements about M protein is FALSE?

It is readily digested by phagocytes

The Limulus amoebocyte assay is used to detect minute amounts of endotoxin in drugs and medical devices.

True

The M protein enhances the virulence of Streptococcus by preventing phagocytosis.

True

Cytopathic effects, such as inclusion bodies and syncytium formation, are the visible signs of viral infections.

True

Cytopathic effects are changes in host cells due to

viral infections.

Bacteria such as E. coli and Salmonella produce invasins that bind host cells, thus causing the cells to

engulf the bacteria.

In general, the LD₅₀ for exotoxins is much greater than the LD₅₀ for endotoxins.

False

A pathogen that is capable of antigenic variation can ________________.

avoid host immune defenses

Many pathogens use the same portal for entry and exit from the body.

True

Cholera toxin polypeptide A binds to surface gangliosides on target cells. If the gangliosides were removed,

polypeptide B would not be able to enter the cells.

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

mucous membranes onlySubmit

Endotoxins are

part of the gram-negative cell wall.Submit

In which of the following cases would the Limulus amebocyte lysate (LAL) assay be used?

to ensure that a sterilized medical device is free of endotoxin

Biofilms provide pathogens with an adhesion mechanism and aid in resistance to antimicrobial agents.

True

Infections with some viruses may induce chromosomal changes that alter the growth properties of host cells.

True

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

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

In A-B exotoxins, the A component binds to the host cell receptor so that the B component can enter the cell.

False

Which of the following statements is FALSE?

Coagulase destroys blood clots.Submit

Which is NOT specifically employed by pathogens to avoid destruction by phagocytosis?

producing superantigens

The most frequently used portal of entry for pathogens is the

mucous membranes of the respiratory tract.

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.

Patients developed inflammation a few hours following eye surgery. Instruments and solutions were sterile, and the Limulus assay was positive. The patients' inflammation was due to

endotoxin

Botulism is caused by ingestion of a proteinaceous exotoxin; therefore, it can easily be prevented by

boiling food prior to consumption.

Symptoms of intense inflammation and shock occur in some gram-positive bacterial infections due to

superantigens

Which organism in the table most easily causes an infection?

Legionella pneumophila

Endotoxins in sterile injectable drugs could cause

septic shock symptoms.Submit

Most pathogens that gain access through the skin

enter through hair follicles and sweat ducts.

Which type of bacterial enzyme helps spread Streptococcus pyogenes by digesting blood clots?

fibrinolysin

All of the following contribute to a pathogen's invasiveness EXCEPT

toxins

The ID₅₀ is

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

Siderophores are bacterial proteins that compete with the host's

iron-transport proteins.

Antibiotics can lead to septic shock if used to treat

gram-negative bacterial infections.

Lysogenic bacteriophages contribute to bacterial virulence because bacteriophages

give new gene sequences to the host bacteria.

Which of the following is NOT a cytopathic effect of viruses?

toxin production

All of the following are used by bacteria to attach to host cells EXCEPT

A-B toxins.

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

antigenic variation.