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, conferring resistance to a wide range of beta-lactam antibiotics. They are a type of **beta-lactamase** that can hydrolyze and inactivate various beta-lactam antibiotics, including penicillins, cephalosporins, and aztreonam. ESBLs are primarily found in **Gram-negative bacteria**, such as Escherichia coli and Klebsiella pneumoniae.
**Why the Correct Answer is Right**
The correct answer is related to the mechanism of action of ESBLs. ESBLs are capable of hydrolyzing a broad spectrum of beta-lactam antibiotics, including **penicillins**, **cephalosporins**, and **monobactams** like aztreonam. However, they are generally ineffective against **carbapenems**, which are a class of beta-lactam antibiotics that are stable against most beta-lactamases, including ESBLs.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because ESBLs can hydrolyze penicillins.
**Option B:** This option is incorrect because ESBLs can hydrolyze cephalosporins.
**Option C:** This option is incorrect because ESBLs can hydrolyze aztreonam, a monobactam.
**Why Each Wrong Option is Incorrect (Continued)**
To complete the reasoning: the incorrect options include penicillins, cephalosporins, and monobactams, all of which are susceptible to ESBL hydrolysis.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that ESBL-producing bacteria are often resistant to multiple antibiotics, making treatment challenging. It is crucial to identify ESBL-producing strains to guide appropriate antibiotic therapy, often involving the use of **carbapenems**.
**Correct Answer:** D. Carbapenems.