Shigella species are classically described as non-motile, yet they efficiently spread from one colonic epithelial cell to adjacent cells without ever entering the extracellular space. The protein responsible for this intracellular movement is:

• A IpaB, which inserts into the host plasma membrane
• B ActA, which recruits Arp2/3 along the entire bacterial surface
• C IcsA (VirG), which nucleates actin polymerisation at one pole of the bacterium ✓
• D Peritrichous flagella expressed only inside cells

Explanation

IcsA (VirG) is an outer membrane protein polarised to one end of Shigella that recruits N-WASP and the Arp2/3 complex, driving unipolar actin comet tail formation and propelling the organism into neighbouring cells. ActA is the Listeria monocytogenes equivalent and distributes over the whole surface, making it the best distractor. IpaB is a type III secretion translocon protein involved in entry, and Shigella genuinely lacks flagella.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.