• 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.

• 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.
• 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 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?
C Capsule polysaccharide.
D Outer membrane proteins.
• 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.
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?
B Porin proteins.
C Lipid A.
D Teichoic acid.
• 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.
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?
B Teichoic acid.
C