Antibiotics and Infectious Disease Definitions (Chapter 10)

Question 1

What is an antibiotic?

Answer 1

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

They interfere with some aspect of growth or metabolism of the target bacterium e.g. DNA/protein/bacterial cell wall synthesis and enzyme actions

Question 3

Describe the structure of bacterial cell walls

Answer 3

• They are made of peptidoglycans (long molecules containing peptides and sugars), held together by cross-links that form between them

Question 4

What happens when a newly formed bacterial cell is growing?

Answer 4

1) it secretes enzymes called autolysins, which make little holes in its cell wall
2) these holes allow the wall to stretch so that the new peptidoglycan chains can link together

Question 5

How does penicillin work?

Answer 5

1) Penicillin prevents the peptidoglycan chains from linking up, but the autolysins keep making new holes
2) ∴ the cell wall becomes progressively weaker
3) as bacteria live in watery environments and take up water by osmosis, water enters the cells
4) when the cell walls are weakened they cannot withstand the pressure potential exerted on them by the cell contents ∴ the cells burst and die

Question 6

What does the way penicillin work mean for its use?

Answer 6

• It is only effective against bacteria while they are growing
• It does not affect human cells as our cells don’t have walls
• It does not affect eukaryotic cells as they have different proteins from bacteria

Question 7

Why do Penicillin and other antibiotics not affect viruses?

Answer 7

1) they do not have cell walls
2) they are not living or growing
3) they are inside host cells
4) antibiotics do not act on the protein coat
5) when viruses replicate, they use the host cell’s mechanisms for transcription and translation - antibiotics do not bind to the proteins that host cells use in these processes

Question 8

Why does penicillin have no effect on M.TB?

Answer 8

1) The thick cell wall of this bacterium is not very permeable
2) The bacterium has a gene that codes for an enzyme that catalyses the breakdown of penicillin

Question 9

How can a bacterium prevent being affected by an antibiotic?

Answer 9

1) proteins in the membranes can inactivate antibiotics
2) some bacterial membranes have proteins that pump out antibiotics if they enter cytoplasm
3) sometimes, the antibiotic simply cannot bind to the intended site of action

Question 10

What does it mean if a bacterium is sensitive?

Answer 10

That it is susceptible to that antibiotic

Question 11

What antibiotic resistance mechanisms do soil bacteria have?

Answer 11

They have acquired a gene that codes for an enzyme called beta-lactamase which breaks down a structure in penicillin

Question 12

What exists to control viral infections?

Answer 12

Antivirals

Question 13

What is an infectious disease?

Answer 13

Diseases caused by pathogens (can be transmitted from infected humans/animals to uninfected humans)

Question 14

What are non-infectious diseases?

Answer 14

Diseases not caused by pathogens

Question 15

What are some examples of non-infectious diseases?

Answer 15

1) long-term degenerative diseases e.g lung cancer
2) inherited or genetic diseases e.g. sickle cell anaemia
3) deficiency diseases caused by malnutrition
4) mental diseases

Question 16

What is a disease?

Answer 16

An illness or disorder of the body or mind that leads to poor health - each disease is associated with a set of signs and symptoms

Question 17

Why can some infectious diseases only spread by direct contact?

Answer 17

Because the pathogen cannot survive outside the human body

Question 18

In what mediums can certain pathogens survive in?

Answer 18

Water, human food, faeces or animals

Question 19

What are carriers?

Answer 19

• People without symptoms, who may spread a pathogen even though they do not have the disease themselves
• They can be difficult to trace as a source of infection

Question 20

What happens when someone takes Penicillin to treat a bacterial infection?

Answer 20

1) bacteria that are susceptible to Penicillin will die

2) in most cases, if the dose is followed correctly, this will be the entire population of bacteria

Question 21

When does antibiotic resistance arise?

Answer 21

When an existing gene within the bacterial genome changes spontaneously to give rise to a nucleotide sequence that codes for a slightly different protein that is not affected by or protects from the antibiotic (i.e. when there is a mutation in the bacterial genome)

Question 22

How can bacteria become resistant to antibiotics?

Answer 22

1) if the dose of Penicillin is not followed (e.g. bc people stop taking it when they feel better as the symptoms disappear) then some susceptible bacteria survive
2) if any mutations occur these might confer resistance
3) these bacteria have a selective advantage and so will survive and reproduce while the others are killed
4) the next time there is an infection with this strain of bacteria, penicillin might not be effective

Question 23

What does a mutant gene have an immediate effect on any bacterium possessing it?

Answer 23

Bc bacteria only have one copy of each gene, since they only have a single loop of double-stranded DNA

Question 24

Describe vertical transmission of antibiotic resistance

Answer 24

1) bacteria reproduce asexually by binary fission (DNA is replicated and each daughter cell receives one copy)
2) this happens rapidly in ideal conditions
3) ∴ a large population of penicillin-resistant bacteria would result

Question 25

Describe horizontal transmission of antibiotic resistance

Answer 25

1) if genes for resistance occur on plasmids or part of the DNA from the bacterial chromosome, these can be transferred between bacteria
2) this happens during conjugation, when a tube forms between 2 bacteria to allow the movement of DNA
3) during conjugation, plasmids are transferred from the donor bacterium to the recipient bacterium

Question 26

What is the consequence of horizontal transmission?

Answer 26

• It is possible for antibiotic resistance to arise in one species and be passed onto another
• Antibiotic resistance may first appear in non-pathogenic bacteria, but then be passed to a pathogenic species

Question 27

What happens the more we misuse antibiotics?

Answer 27

The greater the selection pressure we exert on bacteria to evolve resistance to them

Question 28

Describe multiple resistance of bacteria

Answer 28

1) if bacteria have plasmids carrying resistance genes for several different antibiotics, they have multiple resistance
2) problem e.g. with MRSA which caused dangerous infections after surgery

Question 29

How can antibiotics be carefully chosen?

Answer 29

Testing antibiotics against the strain of bacterium isolated from people ensures that the most effective antibiotic can be used in treatment

Question 30

Why is there a constant search for new antibiotics?

Answer 30

Because of the developing resistance

Question 31

Why can scientists make semi-synthetic antibiotics to extend the range available?

Answer 31

A bacterium resistant to a particular antibiotics may not be resistant to an antibiotic with a slightly altered chemical structure

Question 32

What are 7 ways that we can reduce the number of circumstances in which bacteria develop resistance to antibiotics?

Answer 32

1) using antibiotics only when appropriate and necessary (not prescribing them for viral infections)
2) reducing the number of countries in which antibiotics are sold without a doctor’s prescription
3) avoiding the use of wide-spectrum antibiotics by using an antibiotic specific to the infection (narrow spectrum)
4) making sue that patients complete course of medication
5) making sure that patients do not keep unused antibiotics for self-medication in the future
6) changing the type of antibiotics prescribed for certain diseases so that the same antibiotic is not always prescribed for the same disease
7) avoiding using antibiotics to prevent, rather than cure, infections

Question 33

What is the transmission cycle?

Answer 33

The way in which a pathogen passes from one host to another

Question 34

What are endemic diseases?

Answer 34

Disease that are always in populations

Question 35

What is the incidence of a disease?

Answer 35

The number of people who are diagnosed over a certain period of time

Question 36

What is the prevalence of a disease?

Answer 36

The number of people who have that disease at any one time

Question 37

When does an epidemic occur?

Answer 37

When there is a sudden increase in the number of people with a disease

Question 38

When does a pandemic occur?

Answer 38

When there is an increase in the number of cases throughout a continent or across the world

Question 39

What is mortality?

Answer 39

The death rate from different diseases

Question 40

What do control methods e.g. vaccination do?

Answer 40

Attempt to break transmission cycles by removing the conditions that favour the spread of the pathogen

Question 41

When is control possible?

Answer 41

Only once the cause of the disease and its method of transmission are known and understood