A 22-year-old college student comes to the student health clinic complaining of a persistent, dry cough, low-grade fever, and fatigue for the past 10 days. Physical examination reveals mild pharyngeal erythema and scattered rales over the lower lung fields. Chest radiography demonstrates bilateral patchy interstitial infiltrates. The physician prescribes a macrolide antibiotic, noting that the most likely causative organism is intrinsically resistant to penicillins and cephalosporins. Which of the following best describes the structural characteristic responsible for this organism's intrinsic antimicrobial resistance?
- Absence of a peptidoglycan cell wallAnswer
- BProduction of extended-spectrum beta-lactamases
- CExpression of altered penicillin-binding proteins
- DPresence of a mycolic acid-rich cell envelope
- EUpregulation of multidrug transmembrane efflux pumps
Answer
Absence of a peptidoglycan cell wall
The correct answer is the absence of a peptidoglycan cell wall. The patient's clinical presentation (prolonged dry cough, low-grade fever, patchy interstitial infiltrates in a young adult) is highly characteristic of 'atypical pneumonia,' most commonly caused by Mycoplasma pneumoniae. Beta-lactam antibiotics, such as penicillins and cephalosporins, function by inhibiting peptidoglycan cross-linking during cell wall synthesis. Because Mycoplasma species naturally lack a cell wall (instead having a cell membrane containing sterols), they are intrinsically resistant to all beta-lactam antibiotics. Macrolides, which inhibit bacterial protein synthesis by binding to the 50S ribosomal subunit, are therefore used for treatment.
Step-by-Step Solution
Key Concept
Intrinsic resistance of Mycoplasma pneumoniae to beta-lactam antibiotics is due to its natural lack of a peptidoglycan cell wall.
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