•
Which organism below, if present in only one of three blood cultures
from a single patient, is most likely to represent contamination caused by poor
antiseptic technique, rather than genuine infection?
A Staphylococcus
epidermidis.
B Streptococcus pneumoniae.
C Escherichia coli.
D Pseudomonas aeruginosa.
E Haemophilus influenzae.
•
Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria
meningitidis all colonize the upper respiratory tract and can spread from there
to the bloodstream and/or meninges. What essential virulence factor, that aids
such spread, is produced by all three organisms?
A IgA protease.
B Polysaccharide
capsule.
C Thick peptidoglycan.
D Endotoxin.
E Exotoxin.
•
Three days after an appendectomy, the patient develops high fever. The
patient's vital signs include a dangerously low blood pressure. The patient's
erythrocyte sedimentation rate (ESR) is above-normal. Which of the cytokines
below most directly contributed to development of these symptoms?
A IL-4
B IFN-gamma
C IL-8
D IL-10
E TNF-alpha
•
A patient began to receive intravenous antibiotics dissolved in
sterile saline solution developed fever within an hour. (The solution in which
antibiotics were dissolved had been sterilized by autoclaving.) The IV infusion
was stopped and the fluid cultured, but cultures on a variety of media were
sterile. Which of the following
bacterial components would have been most effective in producing the patient's
fever?
A Spores
B Lipopolysaccharide.
C Capsule polysaccharide.
D Outer membrane proteins.
E Siderophores.
•
Cells of pathogenic Gram-negative bacteria often have 'common pili'
extending from their surfaces. What process is promoted by these pili?
A Adherence
of bacteria to mammalian cells.
B Inhibition of Complement activation.
C Resistance to opsonization by antibodies.
D Transfer of DNA between bacterial cells.
E Transport of nutrients into bacterial
cells.
•
Water used to prepare solutions for intravenous use must not only be
sterile, but also be free of bacterial components. After sterilization, which
bacterial component is it most important to remove?
A Lipids of the plasma (inner) membrane.
B Capsular polysaccharide.
C Spores.
D Lipopolysaccharide.
E Proteases which activate complement.
•
A patient with bacterial infection of the bloodstream developed fever
and shock, produced by lipopolysaccharide (LPS). What part of LPS was
responsible for its toxic effect?
A Long repeating polysaccharide (O-antigen).
B Complex phosphorylated polysaccharide
core.
C Unsaturated fatty acids, released by
hydrolysis.
D Disaccharide
substituted with saturated fatty acids (Lipid A).
E Protein, freed from covalent linkage to
polysaccharide by plasma proteases.
•
Which compound is found in the envelopes of Gram-positive bacteria,
but not in Gram-negatives?
A Peptidoglycan.
B Porin proteins.
C Lipid A.
D Teichoic
acid.
E Capsule
•
Streptococcus pneumoniae is cultured from a patient's sputum. Clinical
isolates of this species typically have thick polysaccharide capsules;
varieties without capsules seldom produce serious disease. How do capsules
increase the ability of S. pneumoniae to cause disease?
A Inhibit binding of antibodies.
B Directly toxic to phagocytic cells.
C Inhibit activation of complement.
D Inhibit
phagocytosis by neutrophils.
E Inhibit antigen presentation by MHC.
F Not immunogenic, but mask immunogenic surface
structure
•
In the immune response to invasive infections by Streptococcus
pneumoniae, antibodies are required for effective defense. Antibodies to which
antigen are most important?
A Teichoic acid.
B Peptidoglycan.
C C-carbohydrate.
D Type III secretion system.
E Polysaccharide
capsule.
•
A child develops severe pharyngitis with purulent exudate and high
fever, consistent with Group A streptococcal infection. He is treated with
Penicillin G, but his parents discontinue the antibiotic after a few days
because he feels much better and does not like to take pills. Some time later
he develops acute rheumatic fever (ARF). Which bacterial antigen provoked the
immune response which caused ARF?
A Peptidoglycan.
B Teichoic acid.
C Group A carbohydrate
D A superantigen protein exotoxin.
E M protein.
•
An important virulence factor of coagulase-positive staphylococci is
Protein A. How does Protein A aid in virulence?
A Binds
the Fc region of IgG, decreases opsonization (Phagocytosis).
B Hydrolyzes secretory IgA.
C Binds Factor H, prevents activation of
complement.
D Extracts iron from plasma proteins.
E Promotes tight binding of bacteria to
extracellular matrix.
•
A notable virulence factor of pathogenic Yersinia is the ability to
paralyze phagocytes and so prevent ingestion of bacteria. What mechanism
enables Yersinia to do this?
A Quorum-sensing system.
B Two component regulatory system.
C Type III
secretion system.
D Iron-acquisition system.
E Phase variation for adhesive pili.
•
One week after surgery to remove an inflamed appendix the patient
develops fever, chills, and hypotension. Anaerobic blood cultures grow
Bacteroides fragilis. What was the most likely source of this infection?
A. Home-grown tomatoes brought to the patient by
his family.
B. Direct contact with a health care worker.
C. Inhalation of airborne spores.
D. Fecal contamination of food or water.
E. The
patient’s own intestinal flora.
•
A febrile patient with E. coli sepsis develops ‘septic shock’. Which of the following is likely to have
played largest role in this reaction?
A. A humoral immune response to bacterial surface
antigens.
B. A cell-mediated immune response to bacteria.
C. Secretion
of cytokines by monocytes in response to stimulation by LPS [endotoxin].
D. Release of granule contents by mast cells and
basophils.
E. Secretion of a bacterial superantigen toxin
that activates TH cells.
•
E. coli and Neisseria meningitidis isolated from blood cultures often
have transport systems (for acquiring metal ions from the environment) lacking
in their less-virulent relatives. Which metal is acquired by the majority of
these systems?
A. Copper
B. Sodium
C. Potassium
D. Magnesium
E. Iron
•
A bacillus cultured from stool produces dark pink colonies on
MacConkey agar. Which of the following
organisms is most likely?
A. Escherichia
coli
B. Salmonella enterica
C. Listeria monocytogenes
D. Shigella sonnei
E. Shigella dysenteriae
•
Fresh liquid cultures of Pseudomonas aeruginosa and Streptococcus
bovis were mixed and Gram-stained. However, the safranin counter-stain was
accidentally omitted. If you looked at this preparation under the microscope,
which line below best describes what you should expect to see?
Cocci
Bacilli
A. Colorless Colorless
B. Blue Pink/red
C. Blue Colorless
D. Pink/red Colorless
E. Pink/red Pink/red
•
Bacteroides fragilisis isolated from an abdominal abscess. Which
phrase below best describes infections like this one?
A. Other
species of bacteria also often present.
B. Initiated by ingestion of spores.
C. Can be successfully treated with
aminoglycosides alone.
D. Contracted by the respiratory route.
E. Sexually-transmitted.
•
A young woman has a urinary tract infection caused by E. coli. By what
route are such infections most commonly acquired?
A. Respiratory route, followed by spread from the
anterior nares.
B. Respiratory route, followed by spread from the
oro-pharyngeal region.
C. Fecal-oral
route, followed by colonization of the intestine and then the perineum.
D. Intestinal infection, followed by spread of
bacteria to the urethra via the bloodstream.
•
Ability of E. coli and related Gram-negative rods to cause intestinal
and urinary-tract infections is promoted by ability of bacteria to adhere
tightly to epithelial cells. Which of the following bacterial structures is
primarily an organelle of adhesion?
A. Outer membrane.
B. Inner membrane.
C. Peptidoglycan.
D. Flagella.
E. Common
pili.
•
A 4-year-old child is brought to the emergency room, stuperous and
unresponsive, with a temperature of 39oC. A lumbar puncture is performed and a
smearof cerebrospinal fluid is Gram-stained. Each high-power field contains
many neutrophils, red cells, and Gram-positive cocci. What does the blue color
of the cocci indicate about the structure of their envelopes?
A. Thick
peptidoglycan.
B. Thin peptidoglycan.
C. Thick capsule.
D. Many adhesive pili.
E. Long O-antigen chains.
•
Sputum is obtained from a patient believed to have tuberculosis,
produced by infection with Mycobacterium tuberculosis, an acid-fast bacterium.
A sputumsmear is stained using the same technique used on the demonstration
slides in the lab. If the patient indeed has Tuberculosis, and the stain is
done with proper procedure, how should the bacteria appear?
A. Cocci, which stain dark red.
B. Cocci, which stain dark green.
C. Cocci, which stain dark blue.
D. Bacilli,
which stain dark red.
E. Bacilli, which stain dark green.
F. Bacilli, which stain dark blue.
•
A six-month old boy develops bloodstream infection with a
Gram-negative bacterium and rapidly develops high fever and hypotension. There
is no pasthistory of similar infections. Which of the following was most
greatly responsible for the fever and hypotension?
A. Capsule polysaccharide, which activated
Complement by the Alternate Pathway.
B. Binding of IgG antibodies to bacteria, which
activated Complement by the Classical Pathway.
C. Lipopolysaccharide,
which bound to Toll-like receptors.
D. Common pili, which allowed bacteria to bind
tightly to endothelial cells.
E. Porin proteins, which allowed bacterial toxins
to exit the periplasm.
•
Patients with bloodstream infections with Gram-positive bacteria can
develop septic shock. Which inflammatory
components are present inthe envelopes of Gram-positive bacteria?
A. Core and Lipid A of Lipopolysaccharide.
B. O-antigen chains of Lipopolysaccharide.
C. Porin proteins and periplasmic lipoproteins.
D. Peptidoglycan
and teichoic acids.
•
Bacteria of the genus Mycoplasmalack all envelope components external
to the plasma membrane. How would you
expect this unusual structural feature to affect their biology?
A. Their Lipid A should produce intense
inflammation.
B. They should be highly-resistant to osmotic
lysis.
C. They
should be resistant to penicillin and structurally-related drugs.
D. They should stain Gram-positive.
E. Absence of an outer membrane means that they
must lack a respiratory chain.
