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.