Bacteria And Disease

Question 1

What is culturing a micro organism

Answer 1

Growing large numbers of the micro organisms so they can be measured in some way

Question 2

What are the risks of culturing micro organisms

Answer 2

-Even if the micro organism is harmless there is a risk of a mutant strain arising that may be pathogenic
-There is a risk of contamination of the culture by pathogenic micro organisms from the environment

Question 3

What is a selective medium

Answer 3

A medium in or on which only a select group of micro organisms with those particular requirements will grow

Question 4

How do you inoculate an agar plate

Answer 4

Sterilise the inoculating loop by holding it in the bunsen burner until it glows red hot and then leave it to cool
Dip the sterilised loop in the suspension of the bacteria
Streak the loop across the surface of the agar, avoiding digging into the agar
Replace the Petri dish lid, tape closed and label
Turn the dish upside down

Question 5

How to grow a pure culture

Answer 5

Grow a culture under conditions only the bacteria you want to culture will survive in e.g. anaerobic conditions to grow anaerobic bacteria

Question 6

How can you count bacteria and single celled fungi

Answer 6

With a microscope and a haemocytometer

Question 7

What is a haemocytometer

Answer 7

A specialised thick microscope slide with a rectangular chamber that holds a standard volume of liquid. The chamber is engraved with a grid of lines.

Question 8

What stain is used when using a haemocytometer, and what are the benefits of this?

Answer 8

Trypan blue - it stains the dead cells dark blue so you can count the living cells

Question 9

What are optical methods of counting cells?

Answer 9

Turbidity

Question 10

What is turbidimetry

Answer 10

A specialised form of colorimetry.
As the numbers of bacterial cells in a culture increase it becomes more turbid.
As a solution gets more turbid it absorbs more light so less light passes through it.
A colorimeter measured the turbidity showing how much light is absorbed and therefore how many micro organisms are present.
A calibration curve is then produced by growing a control culture and taking samples at regular time intervals.

Question 11

What is dilution plating

Answer 11

A method used to find the total viable cell count.
It involves diluting a culture to a point where the colonies can be counted.
The accuracy of this can be checked using a haemocytometer

Question 12

How to measure growth of fungi when culturing

Answer 12

Measure the diameter of the patches of mycelium.
This can be used to compare growth rate in different conditions.

Question 13

What is the generation time

Answer 13

The time between bacterial divisions

Question 14

Why do we use a logarithmic scale when considering the growth of bacteria

Answer 14

Because bacteria grows exponentially so the numbers are enormous, therefore the only way to capture this on a scale is when its logarithmic.

Question 15

What are the 4 stages in a growth curve and what are they

Answer 15

Lag phase - when bacteria are adapting to their new environment and are not reproducing at their maximum rate
Log phase - when the rate of bacterial reproduction is at its theoretical maximum (doubling)
Stationary phase - when the total growth rate is 0 as the number of new cells is equal to the number of deaths
Death phase - when reproduction has almost ceased and the death rate of cells is increasing

Question 16

What are the reasons for a slow in growth rate of bacteria

Answer 16

A reduction in the amount of nutrients available
A build up of waste products

Question 17

What are the two main types of toxins bacteria release

Answer 17

Endotoxins and exotoxins

Question 18

Endotoxins

Answer 18

Lipopolysaccharides that are part of the outer layer of the cell wall of gram negative bacteria.
The lipid part causes disease.
Bacterial endotoxins can cause salmonella spp.
Antibiotic treatment can lead to further endotoxin release due to lysis of the cell wall, meaning the lipopolysaccharide component is released.

Question 19

Salmonella spp.

Answer 19

Can’t be treated with antibiotics, they usually just reduce symptoms.
Best way to deal with salmonella spp. is to avoid it by washing hands after handling raw meat, cooking meat thoroughly etc.

Question 20

Exotoxins

Answer 20

Usually soluble proteins produce and released by bacteria.
Produced by both gram positive and gram negative bacteria.
The effects can be more widespread than endotoxins: some damage cell membranes causing cell breakdown or internal bleeding, some act as competitive inhibitors or neurotransmitters, some directly poison cells.

Question 21

Staphylococcus spp.

Answer 21

Only cause disease if they get inside tissues of the body or the person has a compromised immune system.
Gram positive bacteria that produce exotoxins which can cause anything from mild skin diseases to rapid death.
Can be treated with antibiotics if diagnosed quickly.
Becoming increasingly resistant to antibiotics.

Question 22

What is host tissue invasion

Answer 22

A third way in which bacteria act as pathogens, in which they invade host tissues and damage cells.
It is the response of the host organism to the cell damage that causes the symptoms of disease.

Question 23

Mycobacterium tuberculosis

Answer 23

Spread by droplet infection.
People who have a compromised immune system are more prone to TB.
It affects the respiratory system and also suppresses the immune system so the body can’t respond.
Primary infection - invade the cells of the lungs and multiply slowly.
Immune response forms a mass of tissue called a tubercle containing dead bacteria and macrophages.
Immune system usually controls the bacteria after 8 weeks.
Mycobacterium tuberculosis is adapted to avoid the immune system and survive the primary infection stage, staying dormant until the person has a suppressed immune system.

Question 24

What is selective toxicity

Answer 24

A substance is toxic against some types of cells or organisms but not others, how antimicrobial drugs work

Question 25

Action of sulfonamides

Answer 25

Antimetabolites interrupt metabolic pathways such as blocking nucleic acid synthesis causing death

Question 26

Action of tetracyclines, chloramphenicol

Answer 26

Protein synthesis inhibitors interrupt or prevent transcription or translation of microbial genes so protein production is affected

Question 27

Action of beta lactams e.g. penicillin

Answer 27

Cell wall agents prevent formation of cross linking in cell walls so bacteria are killed by lysis

Question 28

Action of some penicillins, cephalosporins

Answer 28

Cell membrane agents damage the cell membrane so metabolites leak out or water moves in, killing the bacteria

Question 29

Action of quinolone

Answer 29

DNA gyrase inhibitors stop bacterial DNA coiling up so it no longer fits with the bacterium

Question 30

What is bacteriostatic

Answer 30

The antibiotic completely inhibits the growth of the microorganisms
Tetracycline is bacteriostatic