If a gene encoding a bacterial transpeptidase enzyme undergoes mutation, which of the following antimicrobials may no longer be effective against the mutated bacterium?
a. Macrolides
b. Polypeptide drugs
c. Tetracyclines
d. Penicillins
e. Quinolones

Verified step by step guidance

1. Step 1: Understand the role of the bacterial transpeptidase enzyme. This enzyme is crucial for bacterial cell wall synthesis because it catalyzes the cross-linking of peptidoglycan chains, which provides structural integrity to the bacterial cell wall.
2. Step 2: Identify which class of antimicrobials targets the transpeptidase enzyme. Beta-lactam antibiotics, such as penicillins, inhibit transpeptidase by binding to its active site, preventing cell wall cross-linking and leading to bacterial cell death.
3. Step 3: Recognize that a mutation in the gene encoding transpeptidase can alter the enzyme's structure, potentially reducing the binding affinity of beta-lactam antibiotics and rendering them less effective or ineffective.
4. Step 4: Review the other antimicrobial classes listed: macrolides inhibit protein synthesis by binding to the 50S ribosomal subunit; polypeptide drugs disrupt cell membrane integrity; tetracyclines inhibit protein synthesis by binding to the 30S ribosomal subunit; quinolones inhibit DNA gyrase and topoisomerase IV involved in DNA replication. None of these directly target transpeptidase.
5. Step 5: Conclude that the antimicrobial class most likely to be ineffective due to mutation in the transpeptidase gene is penicillins, as their mechanism of action depends on binding to this enzyme.

Key Concepts

Bacterial Transpeptidase Enzyme

Transpeptidase enzymes, also known as penicillin-binding proteins (PBPs), are crucial for bacterial cell wall synthesis. They catalyze the cross-linking of peptidoglycan chains, providing structural integrity. Mutations in these enzymes can alter their binding sites, affecting the action of certain antibiotics.

Mechanism of Action of Penicillins

Penicillins target bacterial transpeptidase enzymes by binding to their active sites, inhibiting cell wall synthesis and causing bacterial death. If the transpeptidase is mutated, penicillins may no longer bind effectively, leading to antibiotic resistance.

Antibiotic Classes and Their Targets

Different antibiotics target distinct bacterial structures or functions: macrolides inhibit protein synthesis by binding the 50S ribosomal subunit; tetracyclines block the 30S subunit; polypeptide drugs disrupt cell membranes; quinolones inhibit DNA gyrase. Only penicillins directly target transpeptidase enzymes.