Match each clinical scenario of antimicrobial treatment failure with the primary molecular or cellular mechanism responsible for the pathogen's resistance.
- An adult patient with Enterococcus faecalis infective endocarditis remains bacteremic despite appropriate dosing of ampicillin and gentamicin; the isolate exhibits high-level gentamicin resistance.Acquisition of genetic elements encoding bifunctional enzymes that chemically inactivate the drug through structural group transfers, preventing its binding to the 30S ribosome.
- A patient receiving prolonged intravenous vancomycin for methicillin-resistant Staphylococcus aureus (MRSA) osteomyelitis develops a relapse of bacteremia; laboratory analysis confirms a vancomycin-intermediate S. aureus (VISA) phenotype.Adaptive structural modification resulting in excessive synthesis of peptidoglycan layers, creating a physical barrier that traps the drug extracellularly.
- A nursing home resident treated for Klebsiella pneumoniae urosepsis fails to respond clinically to ceftriaxone; the pathogen is subsequently found susceptible to imipenem but resistant to most cephalosporins.Production of plasmid-borne hydrolytic enzymes capable of cleaving the core ring structure of advanced-generation penicillins and cephalosporins, but typically inhibited by clavulanate.
- An intubated patient being treated for Pseudomonas aeruginosa pneumonia experiences treatment failure with meropenem; the isolate demonstrates new resistance to carbapenems but remains susceptible to antipseudomonal cephalosporins.Spontaneous mutational repression or loss of specific transmembrane porin proteins, effectively denying the drug access to the periplasmic space.
- An ambulatory patient with typical features of Streptococcus pneumoniae pneumonia fails to improve after a course of oral azithromycin; culture results later demonstrate macrolide resistance.Conformational change induced by post-transcriptional methylation of the 23S ribosomal RNA, which drastically lowers the affinity of the target binding pocket for the drug.
Answer
The correct pairings successfully match each distinct clinical presentation of antibiotic failure to its specific underlying genetic or structural resistance mechanism (e.g., Enterococcus HLAR with modifying enzymes, VISA with thickened cell wall, ESBL with hydrolytic enzymes).
Each clinical scenario highlights a distinct, pathogen-specific mechanism of antimicrobial resistance that maps perfectly to the known molecular pathways of those specific drug classes.
Step-by-Step Solution
Key Concept
Molecular mechanisms of antimicrobial resistance in high-yield clinical pathogens.
Estimated Time:2m 30s