Unit 6- Antibiotics

Question 1

What types of antibiotics are there?

Answer 1

Bactericidal - kills bacteria

Bacteriostatic - prevents growth

Question 2

How do bactericidal antibiotics work?

Answer 2

Kill bacteria by interfering with its biochemistry or structure

Question 3

Give an example of a bactericidal antibiotic and how it works

Answer 3

Penicillin
Inhibits transpeptidase, an enzyme that makes cross links in the peptidoglycan cell wall
Meaning cells can’t withstand turgid pressure so burst due to osmotic lysis
This also only targets gram positive bacteria so is a narrow spectrum antibiotic

Question 4

How do bacteriostatic antibiotics work?

Answer 4

Prevent the growth and reproduction of bacteria so the immune system can deal with the infection

Question 5

Give an example of a bacteriostatic antibiotic: and whether it’s broad or narrow spectrum

Answer 5

Tetracycline

• binds to a bacterial ribosomes blocking the attachment of tRNA, stopping protein synthesis, and does not affect mammalian ribosomes
• this affects all bacteria so is a broad spectrum antibiotic

Question 6

What are antibiotics

Answer 6

Chemicals that target differences in structure or biochemistry between bacterial and mammalian cells into order to stop growth of bacterial cells

Question 7

How do we test the effectiveness of antibiotics?

Answer 7

• a bacterial lawn is made on an agar plate, using a pure sample of bacteria from a patient
• disks of filter paper are soaked in the different antibiotics then applied to the agar
• the antibiotics diffuse out leaving a one of inhibition
• the larger the zone the more effective the antibiotic

Question 8

Why does a larger inhibition zone mean a more effective antibiotic?

Answer 8

As the antibiotic diffuses out the disc it’s concentration decreases
A larger inhibition zone means the antibiotic kills bacteria at a lower concentration

Question 9

How may a bacteria population develops resistance to an antibiotic?

Answer 9

• resistance developers from a random mutation
• in most cases a mutation is fatal but rarely the mutation makes the bacteria resistant to an antibiotic
• when a population is exposed to the antibiotic the mutated bacterium and its off spring will be the only survivors
• they will produce a new population all with antibiotic resistance

Question 10

How can antibiotic resistance spread?

Answer 10

Vertical gene transfer

Horizontal gene transfer

Question 11

What is vertical gene transfer?

Answer 11

Dividing by binary fission and Passing a gene on to its offspring

Question 12

What is horizontal gene transfer?

Answer 12

Bacteria can transfer genes between each other and other species by conjugation
This is the transfer of DNA (plasmids) between 2 bacterial cells
This means antibiotic resistant genes can be transferred readily

Question 13

How can a bacteria be resistant to multiple different antibiotics?

Answer 13

It’s unlikely a bacteria will mutate twice to get double resistance
So horizontal gene transfer

Question 14

What measures can be taken to stop the spread of resistant bacteria?

Answer 14

• only use antibiotics when absolutely necessary
• every antibiotics course should be completed
• improve hospital hygiene
• stop using antibiotics in animal feed
• use a wider range of antibiotics

Question 15

Give some hygiene measures hospitals can take to avoid spread of disease

Answer 15

• use alcohol based gels
• wear clean clothing
• thorough cleaning of hospital wards
• isolating infected patients
• screening patients for infection as they enter the hospital

Question 16

For a pathogen to cause a disease what steps are there?

Answer 16

• transmission to host
• entry into host
• evasion of hosts defences
• invasion and reproduction inside the host
• harm the host by releasing exotoxins or endotoxins

Question 17

What are toxins?

Answer 17

Chemicals that interfere with the body’s chemical reactions by inhibiting enzymes, binding to receptors etc

Question 18

Exotoxins:

Answer 18

Proteins secreted by bacteria
Spread through host via blood or body fluids
These toxins have various effects, eg diarrhoea, paralysis

Question 19

What does staphylococcus’ exotoxin do?

Answer 19

Overstimulates the non specific immune response leading to a huge inflammatory effect sometimes fatal

Question 20

Endotoxins:

Answer 20

Lipopolysaccharides in the membrane of gram negative bacteria
These are released when the bacteria is broken down by host generally causing a localised effect

Question 21

Explain why S.aureus is likely to ave a wider effect on the body early in an infection than salmonella?

Answer 21

S. aureus produces exotoxins that are passed to host tissues and fluids to affect many parts of the body
Salmonella endotoxins have their effect at the site of infection as they remain fixed to the bacterium

Question 22

Tuberculosis:
Transmission:
Symptoms:
Treatment:

Answer 22

Transmission: droplets from cough and sneezing
Symptoms: coughing blood, harsh coughing, weight loss, fever
Treatment: antibiotics

Question 23

How does TB infect cause infection?

Answer 23

1- latent tuberculosis
Bacterial cells invade epithelial cells of alveoli, macrophages attempt to destroy the bacteria but they are protected by waxy coat and multiply to form lumps (tubercles) in the lungs, the bacteria is dormant
2- active tuberculosis
After a delay bacteria emerges from tubercles, and spreads in blood stream to other organs killing the cells of each organ causing weakness