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Chapter 43: Beta-Lactam Antibiotics & Other Cell Wall Synthesis Inhibitors

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The primary mechanism of antibacterial action of the penicillins involves inhibition of

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(A) Beta-lactamases

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(B) Cell membrane synthesis

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(C) N-acetylmuramic acid synthesis

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(D) Peptidoglycan cross-linking

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(E) Transglycosylation

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Penicillins (and cephalosporins) bind to PBPs acting at the transpeptidation stage of cell wall synthesis (the final step) to inhibit peptidoglycan cross-linking. The beta-lactam antibiotics also activate autolysins, which break down the bacterial cell wall. Synthesis of N-acetylmuramic acid is inhibited by fosfomycin. Vancomycin inhibits transglycolase, preventing elongation of peptidoglycan chains. The answer is D.

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A 33-year-old man was seen in a clinic with a complaint of dysuria and urethral discharge of yellow pus. He had a painless clean-based ulcer on the penis and nontender enlargement of the regional lymph nodes. Gram stain of the urethral exudate showed gram-negative diplococci within polymorphonucleocytes. The patient informed the clinic staff that he was unemployed and had not eaten a meal for 2 d.

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The most appropriate treatment of gonorrhea in this patient is

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(A) A single intramuscular dose of ceftriaxone

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(B) Amoxicillin orally for 7 d

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(C) Procaine penicillin G intramuscularly as a single dose plus oral probenecid

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(D) Meropenem orally for 7 d

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(E) Vancomycin intramuscularly as a single dose

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Treatments of choice for gonorrhea include a single dose of ceftriaxone (intramuscularly). Because of the high incidence of beta-lactamase-producing gonococci, the use of penicillin G or amoxicillin is no longer appropriate for gonorrhea. Similarly, many strains of gonococci are resistant to tetracyclines. Alternative drugs (not listed) for gonorrhea include cefixime, azithromycin (see Chapter 44) or spectinomycin (see Chapter 45). The answer is A.

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A 33-year-old man was seen in a clinic with a complaint of dysuria and urethral discharge of yellow pus. He had a painless clean-based ulcer on the penis and nontender enlargement of the regional lymph nodes. Gram stain of the urethral exudate showed gram-negative diplococci within polymorphonucleocytes. The patient informed the clinic staff that he was unemployed and had not eaten a meal for 2 d.

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Immunofluorescent microscopic examination of fluid expressed from the penile chancre of this patient revealed treponemes. Because he appears to be infected with Treponema pallidum, the best course of action would be to

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(A) Administer a single ...

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