beta – Lactamases cause resistance to penicillins and cephalosporins by
**Core Concept**
Beta-lactamases are enzymes that catalyze the hydrolysis of beta-lactam antibiotics, resulting in the cleavage of the beta-lactam ring. This action inactivates the antibiotic, rendering it ineffective against bacterial infections.
**Why the Correct Answer is Right**
Beta-lactamases, particularly TEM-1 and SHV-1, are responsible for conferring resistance to penicillins and cephalosporins. These enzymes recognize the beta-lactam ring of the antibiotic and cleave it, resulting in the inactivation of the antibiotic. The mechanism of beta-lactamase action involves the formation of a covalent acyl-enzyme intermediate, which is then hydrolyzed to release the inactivated antibiotic.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because beta-lactamases do not cause resistance to aminoglycosides, which are a different class of antibiotics. Aminoglycosides work by inhibiting protein synthesis through binding to the 30S ribosomal subunit.
**Option B:** This option is incorrect because beta-lactamases do not cause resistance to quinolones, which are a class of antibiotics that work by inhibiting DNA gyrase and topoisomerase IV. Quinolones act by interfering with bacterial DNA replication and transcription.
**Option C:** This option is incorrect because beta-lactamases do not cause resistance to macrolides, which are a class of antibiotics that work by inhibiting protein synthesis through binding to the 50S ribosomal subunit. Macrolides bind to the ribosome and prevent the translocation of the ribosome along the mRNA.
**Clinical Pearl / High-Yield Fact**
Beta-lactamases are often encoded by plasmids, which can be transferred between bacteria, resulting in the spread of resistance. This highlights the importance of antibiotic stewardship and the need to monitor antibiotic resistance patterns in clinical settings.
**Correct Answer: D. Beta-lactam antibiotics.**