Extended-spectrum beta-lactamases (ESBLs) are characterized by activity against all except :
**Core Concept**
Extended-spectrum beta-lactamases (ESBLs) are enzymes produced by certain bacteria, primarily Gram-negative, that confer resistance to a wide range of beta-lactam antibiotics by hydrolyzing the beta-lactam ring. This mechanism of resistance affects multiple classes of beta-lactam antibiotics, including penicillins, cephalosporins, and monobactams.
**Why the Correct Answer is Right**
ESBLs do not typically affect carbapenems, which have a stable beta-lactam ring that is resistant to hydrolysis by ESBLs. This is because carbapenems have a unique molecular structure that makes them less susceptible to hydrolysis by these enzymes. As a result, carbapenems remain effective against bacteria that produce ESBLs.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because ESBLs can hydrolyze many penicillins, including broad-spectrum penicillins like piperacillin and ticarcillin.
**Option B:** Incorrect because ESBLs can also hydrolyze many cephalosporins, including third-generation cephalosporins like ceftriaxone and cefotaxime.
**Option C:** Incorrect because ESBLs can hydrolyze monobactams like aztreonam, although this is less common.
**Clinical Pearl / High-Yield Fact**
When suspecting ESBL-producing bacteria, it is essential to test for carbapenem susceptibility, as these antibiotics are often the last line of defense against these resistant organisms.
**Correct Answer: D. Carbapenems.