Infectious Diseases

Question 1

What is an antibiotic?

Answer 1

An antibiotic is a drug that kills or stops the growth of bacteria without harming the cells of the infected organism.

Question 2

How do antibiotics work?

Answer 2

1. Synthesis of bacterial cell walls - penicillin prevents the synthesis of the cross links between the peptidoglycan polymers in the cell walls of bacteria by inhibiting the enzymes that build these cross links. This means that penicillin is only active against bacteria while they are growing.
2. Activity of proteins in the cell surface membrane - growing bacterial cells produce autolysins, enzymes that create small holes in the cell wall, allowing it to expand as new peptidoglycan is added. Penicillin prevents these peptidoglycan chains from linking, while autolysins continue making holes. This weakens the cell wall, making it unable to withstand turgor pressure from water entering by osmosis, causing the bacteria to burst.
3. Enzyme action.
4. DNA synthesis.
5. Protein synthesis.

Question 3

Why are antibiotics not effective against viruses?

Answer 3

Viruses do not have cell walls. When a virus replicates, it uses the host cells mechanisms for transcription and translation and antibiotics do not bind to the proteins that host cells use in these processes.

Question 4

Why does penicillin have no effect on Mycobacterium tuberculosis?

Answer 4

Mycobacterium tuberculosis has a thick, low-permeability cell wall and a gene that produces an enzyme to break down penicillin.

Question 5

How do some bacteria inactivate antibiotics?

Answer 5

Proteins in bacterial membranes can inactivate antibiotics, preventing them from working.

Question 6

How do bacteria remove antibiotics from their cytoplasm?

Answer 6

Some bacteria have membrane proteins that pump out antibiotics if they enter the cytoplasm.

Question 7

Where are genes for antibiotic resistance often found?

Answer 7

Antibiotic resistance genes often occur on plasmids.

Question 8

Consequences of antibiotic resistance.

Answer 8

The overuse and misuse of antibiotics create a selection pressure, meaning that bacteria with resistance genes are more likely to survive and reproduce. Over time, this leads to the rise of antibiotic-resistant strains, making infections harder to treat and increasing hospital stays, complications, and even the risk of death.

In places where antibiotics are widely used—like hospitals and farms—resistance spreads quickly between bacteria, even across different species. Sometimes, non-harmful bacteria develop resistance first and later transfer these resistance genes to harmful bacteria.

Additionally, some bacteria acquire plasmids carrying multiple resistance genes, making them resistant to several antibiotics at once, which is called multiple resistance. This makes treating bacterial infections even more difficult.

Question 9

Resistance to antibiotics.

Answer 9

1. Enzyme Production – Some bacteria produce enzymes that break down or inactivate antibiotics before they can work. For example, Mycobacterium tuberculosis produces an enzyme that breaks down penicillin.
2. Reduced Permeability – Some bacteria have thicker or less permeable cell walls, making it difficult for antibiotics to enter. For instance, Mycobacterium tuberculosis has a thick, waxy cell wall that prevents antibiotics from reaching their target.
3. Efflux Pumps – Certain bacteria have membrane proteins that actively pump antibiotics out of the cell, preventing them from reaching a high enough concentration to be effective.
4. Modification of Target Sites – Some bacteria alter the structure of their target molecules (such as ribosomes or enzymes), so the antibiotic can no longer bind and disrupt its function.
5. Plasmid-Mediated Resistance – Resistance genes can be carried on plasmids, which are small, circular DNA molecules that can be transferred between bacteria, spreading resistance quickly.

Question 10

Consequences of antibiotic resistance.

Answer 10

1. High Antibiotic Use – Hospitals frequently use a wide range of antibiotics to treat infections. This creates strong selection pressure, allowing only resistant bacteria to survive and multiply. Similarly, prisons often rely on antibiotics for treating infections in overcrowded conditions.
2. Close Contact Between People – Both hospitals and prisons involve crowded living conditions, making it easier for bacteria to spread between individuals through direct contact, shared spaces, and contaminated surfaces.
3. Weakened Immune Systems – Many hospital patients have weakened immune systems due to illness, surgery, or treatments like chemotherapy. This makes them more susceptible to infections, leading to more frequent antibiotic use, which increases the risk of resistance.
4. Poor Hygiene and Sanitation – Prisons may have limited access to hygiene facilities and overcrowding, increasing the spread of resistant bacteria. In hospitals, even with strict hygiene protocols, resistant bacteria can persist on medical equipment, bed linens, and surfaces.
5. Plasmid-Mediated Resistance – Bacteria in these environments can easily exchange resistance genes through plasmids, making multiple species resistant to antibiotics and spreading resistance quickly.