Microbiology MCAT Practice Question
A 68-year-old man with COPD presents to the ED with fever (38.9°C), productive cough, and shortness of breath. Chest X-ray shows left lower lobe consolidation. Sputum culture grows Streptococcus pneumoniae susceptible to penicillin. The patient is treated with amoxicillin and recovers. Six months later, he returns with similar symptoms, and this time the isolated S. pneumoniae strain is penicillin-resistant. Genetic analysis reveals the resistant strain acquired DNA encoding altered penicillin-binding proteins from another pneumococcal strain. This horizontal gene transfer mechanism most likely occurred through which process, and what is the primary evolutionary advantage to the pathogen?
Answer choices
- ATransduction via bacteriophage; allows the bacterium to escape recognition by the host immune system
- BTransformation via uptake of free DNA fragments; enables rapid acquisition of antibiotic resistance and virulence genes under selective pressureCorrect answer
- CConjugation via pili formation; permits bidirectional exchange of chromosomal DNA in a conjugal pair
- DTransposition of mobile genetic elements; increases mutation rate to generate spontaneous resistance
- ECompetence-mediated DNA uptake; allows repair of damaged genes using identical DNA sequences from the same strain
- FRecombination with plasmid DNA; provides temporary antibiotic resistance that is lost after several cell divisions
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