A 32-year-old man presents with right upper quadrant pain, fever, and a large solitary liver abscess on imaging. Aspirated pus is thick and mucoid. Culture grows Klebsiella pneumoniae. Inoculation of the colony onto agar and stretching with a loop draws out a viscous string longer than 5 mm. This string test positivity indicates:

• A Extended-spectrum beta-lactamase production
• B Presence of the rmpA-inactivated avirulent laboratory mutant
• C Mucoid conversion secondary to chronic antibiotic exposure
• D Hypermucoviscosity due to overproduction of capsular material, typical of hypervirulent K. pneumoniae ✓

Explanation

Hypervirulent K. pneumoniae, classically serotypes K1 and K2 and common in East Asia, causes metastatic community-acquired infections including liver abscess, meningitis, and endophthalmitis in young healthy hosts. Overproduction of capsular polysaccharide and regulators such as rmpA confer a hypermucoviscous phenotype demonstrated by a positive string test with a viscous string exceeding 5 mm. ESBL status is unrelated to mucoviscosity and carbapenem-resistant strains are typically hospital acquired.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.