Question 1

Q: A 45-year-old woman with a history of recurrent urinary tract infections presents to the emergency department with fever, flank pain, and dysuria. Urine culture grows Escherichia coli resistant to ampicillin, trimethoprim-sulfamethoxazole, and fluoroquinolones. Molecular testing reveals the presence of a plasmid-encoded CTX-M gene. What is the most likely mechanism by which this organism acquired its resistance pattern?

Horizontal gene transfer via conjugation. ***Horizontal gene transfer via conjugation*** - The **CTX-M gene** is a classic example of an **Extended-Spectrum Beta-Lactamase (ESBL)** typically located on **plasmids**, which are extra-chromosomal DNA molecules. - **Conjugation** is the primary mechanism for the spread of **multidrug resistance** among Enterobacteriaceae because it facilitates the direct transfer of these plasmids between bacteria. *Chromosomal mutation in DNA gyrase* - Mutations in **DNA gyrase** (and topoisomerase IV) primarily account for resistance to **fluoroquinolones**, not beta-lactam resistance via enzyme production. - The scenario specifically mentions a **plasmid-encoded gene**, which rules out a chromosomal mutation as the primary source of the CTX-M gene. *Spontaneous point mutation in penicillin-binding proteins* - Alterations in **Penicillin-Binding Proteins (PBPs)** are common in **Methicillin-resistant Staphylococcus aureus (MRSA)** or Penicillin-resistant Streptococcus pneumoniae. - In gram-negative bacteria like *E. coli*, resistance to advanced beta-lactams is usually due to **beta-lactamase production** rather than PBP mutations. *Transduction by bacteriophage* - **Transduction** involves the transfer of DNA from one bacterium to another by a **viral vector (bacteriophage)**. - While possible, it is not the dominant clinical mechanism for the widespread dissemination of **ESBL-mediated resistance** in *E. coli*. *Transformation with environmental DNA* - **Transformation** is the uptake of **naked DNA** from the environment and is common in naturally competent species like *S. pneumoniae* or *Neisseria*. - *E. coli* is not typically naturally competent in the clinical environment, making this an unlikely pathway for acquiring a **plasmid-encoded CTX-M gene**.

Question

A 45-year-old woman with a history of recurrent urinary tract infections presents to the emergency department with fever, flank pain, and dysuria. Urine culture grows Escherichia coli resistant to ampicillin, trimethoprim-sulfamethoxazole, and fluoroquinolones. Molecular testing reveals the presence of a plasmid-encoded CTX-M gene. What is the most likely mechanism by which this organism acquired its resistance pattern?

Accepted Answer

Horizontal gene transfer via conjugation

Answer

Chromosomal mutation in DNA gyrase

Answer

Spontaneous point mutation in penicillin-binding proteins

Answer

Transduction by bacteriophage

Answer

Transformation with environmental DNA

Microbial genetics and drug resistance — MCQs

Microbial genetics and drug resistance — MCQs

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