peptidoglycan, antibiotics, and resistance

class 11

peptidoglycan

a complez polymer of alternating NAG and NAM sugar residues liked by β-(1,4)- glycosidic bonds that forms a rigid, mesh-like layer in bacterial cell walls

what molecules make up peptidoglycan

repeating sugars called NAG (N-acetylglucosamine) and NAM (N-acetylmuramic acid) linked together

what type of bond connects NAG and NAm

β-1,4 glycosidic bond

What is attached to NAM?

A short amino acid side chain. This varies by species.

How does Gram staining relate to peptidoglycan?

Crystal violet binds to the thick peptidoglycan layer, especially in Gram-positive bacteria.

Why must peptidoglycan be broken and rebuilt?

The cell needs to grow and divide in a process called remodeling

What happens if remodeling enzymes don’t work?

Cells cannot properly divide and may die.

Where does peptidoglycan synthesis occur?

the cytoplasm, the membrane, and the periplasm.

What are PBPs (Penicillin-Binding Proteins) ?

Enzymes that build and cross-link peptidoglycan. They are major targets for antibiotics

Who introduced antiseptic surgery?

Joseph Lister.

Who discovered penicillin?

Alexander Fleming in 1928.

Why was penicillin revolutionary?

It saved millions of lives and became the first major antibiotic.

Do all antibiotics work the same way?

No. They target different parts of bacterial cells.

How does penicillin work?

It binds irreversibly to PBPs and blocks cell wall synthesis.

What type of inhibitor is penicillin?

A suicide inhibitor.

How do bacteria resist penicillin?

They produce β-lactamase, which breaks the antibiotic.

How does methicillin work?

Same mechanism as penicillin.

How do bacteria resist methicillin?

They produce an altered PBP that the drug cannot bind.

What is vancomycin used for?

Treating multidrug-resistant bacteria. It is often a last resort.

What does vancomycin target?

The D-Ala-D-Ala portion of peptidoglycan.

How do bacteria resist vancomycin?

They change D-Ala-D-Ala to D-Ala-D-Lactate.

What is a disk diffusion assay?

A test that measures how well antibiotics inhibit bacterial growth.

What is MIC?

Minimum inhibitory concentration. The lowest amount of drug that stops growth.

What is conjugation?

Transfer of DNA between bacteria through direct contact.

What carries resistance genes during conjugation?

Conjugative plasmids.

What does tetracycline target?

The ribosome. It blocks protein synthesis.

How do bacteria resist tetracycline?

They pump it out using transporters like TetA.

What are efflux pumps?

Proteins that push antibiotics out of the cell.

Why are they important?

They can remove many different drugs, causing multidrug resistance.

Examples of efflux pump families?

RND, MFS, MATE, and ABC transporters.

What are the 4 main ways bacteria resist antibiotics?

1. Reduce drug entry

2. Inactivate the drug

3. Change the target

4. Pump the drug out

What is horizontal gene transfer (HGT)?

Movement of genes between bacteria. Spreads antibiotic resistance quickly

Have bacteria developed resistance to all antibiotics?

Yes, eventually resistance appears to every antibiotic used.

What is heteroresistance?

A subpopulation of bacteria is resistant while others are not.

What happens with incorrect antibiotic use?

It increases resistance and makes infections harder to treat.

What are scientists trying to target now?

• LPS transport

• Peptidoglycan synthesis

• Ribosomes

• Proteases

• Quorum sensing

Why is the bacterial cell envelope a major drug target?

It is essential for survival and different from human cells.

How do peptidoglycan, LPS, and antibiotics connect?

They all relate to the bacterial cell envelope, which is essential and a major drug target.