Klebsiella pneumoniae producing Extended-Spectrum Beta-Lactamases (ESBLs) is identified in a urine culture. Which phenotypic test confirms ESBL production, and which antibiotic class remains reliably active against most ESBL producers?

• A Colistin susceptibility test; polymyxins remain active
• B Modified Hodge test; tigecycline remains reliably active
• C Double-disk synergy test (DDST) with clavulanate; carbapenems remain reliably active ✓
• D AmpC disk test; aztreonam remains reliably active

Explanation

ESBL production is confirmed phenotypically by the Double-Disk Synergy Test (DDST): cefotaxime and ceftazidime disks are placed adjacent to a disk containing clavulanate (a beta-lactamase inhibitor); a 'keyhole' or 'champagne cork' enhancement zone toward clavulanate confirms ESBL. The E-test ESBL gradient method also uses clavulanate inhibition. Carbapenems (imipenem, meropenem, ertapenem) are the drugs of choice for serious ESBL infections as they are not hydrolyzed by ESBLs. Aztreonam susceptibility tests false-positive susceptibility in many ESBL producers.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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