Which mechanism explains why some bacterial infections become untreatable despite initial antibiotic sensitivity?

💡 Explanation

Antibiotic resistance can emerge through horizontal gene transfer of resistance genes. These genes often encode efflux pumps that actively expel the antibiotic from the bacterial cell, thereby reducing its intracellular concentration and effectiveness, because this mechanism is acquired rather than intrinsic. Therefore, the horizontal transfer of genes encoding efflux pumps explains acquired antibiotic resistance, rather than reduced metabolic activity or cell wall changes.

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