A clinical isolate shows multidrug resistance encoded on a genetic element that can jump between plasmids and the bacterial chromosome without requiring sequence homology. Analysis reveals a central region carrying resistance genes bounded by two insertion sequences in the same orientation. This element is best classified as:
- A Insertion sequence element
- B Composite transposon ✓
- C Integron
- D Pathogenicity island
Correct answer: B. Composite transposon
Explanation
B composite transposon such as Tn10 or Tn5 consists of a central segment carrying genes such as resistance determinants, flanked on either side by two insertion sequence (IS) elements in the same or inverted orientation. An insertion sequence alone carries only the transposase gene and inverted repeats, with no accessory genes. Integrons lack their own mobility machinery and depend on transposons or conjugative plasmids for movement.
Reference: Jawetz, Melnick and Adelberg's Medical Microbiology, 28th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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