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Question

Difficulty: MediumInfectious Disease Mechanisms

A hospital's antimicrobial stewardship committee is reviewing mechanisms of antibiotic resistance among distinct bacterial isolates. Match each clinical isolate and its characteristic resistance profile with the primary molecular mechanism responsible for its resistance.

  • Streptococcus pneumoniae with high-level resistance to ceftriaxoneAcquisition of mosaic genes leading to altered penicillin-binding proteins (PBPs)
  • Pseudomonas aeruginosa with isolated resistance to imipenemDecreased outer membrane permeability due to mutational loss of specific porins (e.g., OprD)
  • Klebsiella pneumoniae resistant to all beta-lactams including carbapenems via a plasmidHydrolytic inactivation of the antimicrobial agent by a serine beta-lactamase
  • Mycoplasma pneumoniae intrinsically resistant to penicillins and cephalosporinsComplete intrinsic absence of a peptidoglycan cell wall target

Answer

Streptococcus pneumoniae pairs with altered PBPs; Pseudomonas aeruginosa pairs with loss of porins; Klebsiella pneumoniae pairs with hydrolytic inactivation by a beta-lactamase; Mycoplasma pneumoniae pairs with absence of a cell wall target.
Each bacterial isolate utilizes a distinct, well-characterized mechanism to evade antimicrobial action. S. pneumoniae alters its target site (PBPs). P. aeruginosa restricts drug entry by losing the OprD porin. K. pneumoniae enzymatically destroys the drug via a carbapenemase. M. pneumoniae intrinsically lacks the structural target (cell wall) entirely.

Step-by-Step Solution

1
Identify the pathogen and its specific resistance phenotype from the given left items.
The pathogens are S. pneumoniae, P. aeruginosa, K. pneumoniae, and M. pneumoniae.
Pathogen identification is the first step in determining the likely resistance mechanism.
2
Recall the characteristic molecular mechanism of resistance for each pathogen-drug combination.
S. pneumoniae uses altered PBPs; P. aeruginosa loses OprD for imipenem; K. pneumoniae uses KPC (carbapenemase); M. pneumoniae lacks a cell wall.
Linking the phenotype to the genotype/molecular mechanism is required to make the correct matches.
3
Pair each isolate with the corresponding molecular mechanism on the right.
All four pairs are successfully matched.
Completes the matching requirement of the question.

Key Concept

Molecular mechanisms of antimicrobial resistance in clinically significant bacteria
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Topics

Infectious Disease Mechanisms

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