Topic 6: Microbiology and Pathogens Flashcards Preview

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Flashcards in Topic 6: Microbiology and Pathogens Deck (165):
1

What is a microbial culture?

A method of multiplying microbial organisms by letting them reproduce in a predetermined culture medium under controlled lab conditions

2

What factors must be controlled when making a microbial culture?

Nutrient levels
Oxygen
pH
Temperature

3

What are the main problems when culturing microorganisms?

1 - Harmless microorganisms might mutate to dangerous ones
2 - Pathogens enter and grow - can cause disease
3 - Contamination with unwanted microorganisms will ruin the investigation

4

What precautions should be taken when culturing microorganisms?

Use sterile equipment
Do not remove culture from lab
Dispose of culture safely

5

What does sterile mean?

Being sterile is to be free from living microorganisms and their spores

6

How do you dispose of microorganism cultures safely?

Seal in a plastic bag and sterilise at 120 degrees for 15 minutes under high pressure and then throw it away

7

Outline the method to culture microorganisms

1. Choose a microorganism to culture
2. Obtain a culture of the microorganism
3. Select and make up the nutrient medium
4. Innoculate the medium

8

What are the different types of nutrient medium?

Liquid broth, nutrient agar and selective medium

9

What is nutrient agar?

A solid nutrient elly extracted from seaweed used in Petri dishes

10

How do you make nutrient agar?

Pour nutrient broth and molten agar into a Petri dish and let it set at 50C

11

What is the advantage of agar

Sets at 50C but melts at 90C so you can keep it at a high temperature

12

What is a selective medium?

A growth medium with a specific combination of nutrients so only a certain type of microorganism grows on it

13

Define innoculation

The process by which microorganisms are transferred into a culture medium under sterile conditions

14

Explain how to innoculate a liquid nutrient medium

Innoculating loop scrapes bacteria from solid culture to liquid nutrient broth to form innoculating broth.
Flask stoppered with cotton wool
Incubate at suitable temp
Regularly mix

15

Why do you stopper a flask of liquid culture when culturing it?

To prevent contamination by microorganisms in the air

16

Why do you mix a flask of liquid culture regularly when culture?

To ensure the broth is aerated bc microorganisms need oxygen

17

Explain how to innoculate a solid nutrient medium

Sterilise the innoculating loop in a Bunsen
Dip into bacteria suspension
Streak across agar surface
Replace lid, clse tape and label
Turn upside down

18

What does aseptic mean?

Sterile - free from contamination from harmful bacteria

19

Why are aseptic techniques used when culturing bacteria?

To ensure the procedure is safe and to prevent the contamination of the culture.

20

Give examples of aseptic technique

Using sterile equipment
Using flamed equipment
Replacing the lid of the petri dish as soon as possible

21

What is a pure culture?

A culture containing only one type of microorganism

22

How can a pure culture be made?

Making conditions aerobic/anaerobic depending on organism
Making selective medium specific to it
Reinnoculate a plate with the microorganism on it (identified by using an indicator)

23

What information do we need to measure the growth of a culture?

The number of cells at different times

24

Name some methods used to measure the growth of cultures

Cell count
Dilution plating
Turbidimetry
Size/area

25

What is a cell count?

A method of measuring the growth of cultures of bacteria or single selled fungi

26

What equipment is needed for a cell count?

Haemocytometer
Microscope

27

What is a haemocytometer?

A thick glass microscope slife with a rectangular chamber that holds liquid. It has perpendicular lines

28

What is trypan blue?

A dye that stains dead cells blue and leaves living cells white

29

Why do we dilute cells with trypan blue before putting them into a haemocytometer?

To stain them so counting is easier
To separate the cells to make them easier to count

30

What is the rule for cells on lines when counting cells in a haemocytometer?

Count them if they're on the top or right line
Don't count them if they're on the bottom or left

31

How is a haemocytometer used?

Put under a microscope and viewed under a low power so the cells can be seen

32

Why is it important to not move the haemocytometer when counting?

Will mve the cells so counting becomes incorrect
Air bubble may be introduced

33

What is turbidity?

The cloudiness of a liquid caused by a large number of individual particles in the solution

34

What is turbidimetry?

A method of measuring the concentration of a substance by measuring the amount of light that passes through it. A specialised form of colorimetry

35

What are calibration curves?

Graphs of known concentrations against their absorbances

36

How are calibration curves made?

Control culture is made and samples taken at regular intervals
Put into colorimeter and turbidity is measured
Do cell count of the same sample
Repeat over time
Plot graph of turbidity against cell count and compare unknown turbidities to get cell count directly

37

How is turbidity measured?

The absorbance of light of a sample is measured by a colorimeter

38

What is dilution plating?

A method used to obtain a culture plate with a countable number of bacterial colonies

39

What assumption is made during dilution plating?

One colony comes from one bacterial cell

40

Define total viable cell count

A measure of the number of cells that are alive in a given volume of culture.

41

Why is dilution plating needed?

Because directly counting the number of colonies from a concentrated solution is difficult bc there are so many so they clump together. By dilution you can get a smaller number of cells

42

What calculation can be done to get the total viable cell count?

number of colonies x dilution factor

43

How can you check the accuracy of dilution plating?

Doing a cell count with a haemocytometer

44

What do you do if there are two or more plates with enough colonies to count in dilution plating?

Count the number of colonies in each plate then calculate a mean

45

How can you find the mass of microorganisms/fungi in a culture?

Sample of broth centrifuged/filtered to remove bacteria from liquid
Material dried until mass stabilises
Measure the dry mass overtime
Increase in mass = increase in growth

46

By what process do bacteria reproduce?

Binary fission

47

Define generation time

The time between divisions of a bacteria

48

What kind of scale is used for bacterial growth and why?

A logarithmic scale because the numbers are huge bc bacteria reproduce hella fast

49

What equation can be used to find the number of bacteria in a population?

Nt = No x 2^kt
Nt - no of organisms at time t
No - number of organisms at the start
k - exponentional growth constant
t - time

50

What equation can be used to find the exponential growth constant?

k=(log10Nt - log10No)/(tlog10(2))

51

How can the growth of a bacterial population be shown

A graph with axis time (t) against log10Nt (y)

52

Name the phases in the bacterial growth curve

Lag phase
Log phase
Stationary phase
Death phase

53

Explain the lag phase of the bacterial growth phase

Line is flat because bacteria are adjusting to their environment so growth is slow
Enzymes and genes still activating

54

Explain the log phase of the bacterial growth phase

Bacteria growing really fast
Growth time depends on number of nutrients and amount of space

55

Explain the stationary phase of the bacterial growth phase

Growth rate is zero - new cells forming = cells dying
Nutrients being used up
Waste products starting to build up

56

Explain the death phase of the bacterial growth phase

No. of cells dying exceeds the no of new cells forming
Nutrients have run out
Waste products have built up too high

57

Why doesn't the exponential growth of bacteria continue forever?

Nutrient exhaustion - nutrient levels can't support growth
Build up of waste products - levels can become toxic and inhibits growth (eg CO2 lowers pH)

58

How can bacteria cause infection in the body?

Destroying host tissue
Releasing toxins

59

How does TB cause infection?

Destroys host tissue

60

Name ways bacteria can enter the body

Wounds
Natural openings

61

Name the ways in which bacteria can be transferred

Droplet infection
Vector (intermediate carrier)
Direct contact
Touching the surface someone infected has touched

62

Why do bacteria produce toxins?

By products of their metabolism

63

Name the different types of toxins

Endotoxins
Exotoxins

64

What are exotoxins?

Soluble proteins that are produced and released into the body outside of the bacterial cell

65

What effect do exotoxins have on the body and why?

Widespread effect because they can travel through body fluids so they have a range of effects

66

What are endotoxins?

Lipopolysaccharides in the membrance of Gram negative bacteria that may be released from the bacteria if it breaks down

67

What effects do endotoxins have on the body and why?

Local to the site of infection because the toxins are in the bacteria for the majority of the time

68

What effect does salmonella have on the body?

Inflammation in the gut lining

69

What are antibiotics?

Drugs that destroy microorganisms or prevent them from reproducing

70

What kind of illnesses are antibiotics used for?

Bacterial not viral

71

What is selective toxicity?

Damage is done to the pathogen not the host cell

72

Name the first antibiotic

Penicillin

73

How can antibiotics be classified?

Bacteriocidal or bacteriostatic

74

Define bacteriostatic antibiotics

Completely inhibit the growth of microorganisms

75

Name a bacteriostatic antibiotic and its mechanism

Tetracyline - interferes with protein synthesis in small ribosomes in bacteria

76

Define bacteriocidal antibiotics

Antibiotics that kill bacteria

77

Name a bacteriocidal antibiotic and its mechanism

Penicillin breaks open bacteria cell walls

78

Define broad-spectrum antibiotics

Destroys a wide range of harmful pathogens

79

Define narrow-spectrum antibiotics

Targets one or two pathogens

80

What does the effectiveness of a drug depend on?

Drug concentration
pH
Susceptibility of pathogen (is it antibiotic resistant)
Whether pathogen can destroy the antibiotic

81

What is antibiotic resistance?

When bacteria mutate so drugs are no longer effective on them

82

Why are mutations common in bacteria?

Because bacteria reproduce rapidly

83

How does natural selection lead to antibiotic resistance?

Allele which causes resistance allows bacteria to survive. When bacteria reproduce, the allele is passed on quickly through other generations. Allele frequency increases.

84

What is horizontal transmission?

When bacteria can acquire resistance from other species through the transmission of their plasmids

85

How can we control the spread of antibiotic resistance?

- Prescribe antibiotics sparingly
- Complete the course of antibiotics
-Good hygiene measures:
Alcohol gels in hospitals
Staff wearing clean clothing
Isolating ill patients
Screening patients for infection before they enter the hospital
Monitoring levels of healthcare acquired infections

86

Why are viral infections specific to particular tissues?

Host cells have antigens and only a few viruses have complementary receptors

87

What is influenza

A virus which infects the tissues of the breathing system - especially the lungs

88

What are the modes of transmission of influenza?

Droplet infection
Direct contact with:
-animal droppings
-virus filled mucus
-surfaces contaminated with the virus

89

What are the modes of infection of influenza

Ciliated epithelial cells of the lungs are infected. Viral RNA takes over the cell, reproduces and cell releases viruses and die

90

What are the pathogenic effects of influenza?

Headaches, runny nose, coughing, vomiting, fever etc

91

How is influenxa treated?

No cure but antivirals used to relieve symptoms
Vaccine used as a preventative measure

92

What is stem rust fungus

A fungus which affects cereal crops

93

What are the modes of transmission of stem rust infection

Wind carries pores
Infected plant fragments in the soil

94

What are the modes of infection of stem rust infection

Spores germinate in water on the plant, the fungus enters the plant through stomata and enzymes digest plant cells and nutrients are absorbed

95

What are the pathogenic effects of stem rust fungus

Nutrients lost from plant
Stem weakened
Blisters on leaf surface
Plant loses control over water loss

96

How can stem rust be controlled?

Dont use nitrate rich fertilisers
Use earlier maturing plants
Bigger spaces between plants
Fungicides

97

What is malaria?

Fever caused by a parasite called Plasmodium spp.

98

What is the mode of transmission of malaria?

Mosquito vectors transfers parasite to humans
Mouthpiece pierces the skin and the saliva has anticoagulants so blood doesnt clot while it gets its blood meal.

99

What is the mode of infection of malaria?

Parasites travel to the liver --> RBC --> reproduce asexually then burst out of RBC ---> eventually transmitted back to the mosquito taking the blood meal

100

What are the pathogenic effects of malaria?

Shaking, fever, sweatin
Muscle pains
Liver damage
Anaemia

101

Define an endemic disease

A disease that is constantly present in an area or country

102

Given an example of an endemic disease

Malaria

103

Why is it difficult to treat endemic diseases?

Widespread
Hard to get people to cooperate
No. of hosts
Expensive

104

Name two ways we can control malaria

Prevent bites
Control number of mosquitos

105

How can we prevent mosquito bites

Insect repellents
Mosquito nets with insecticides
Screens on door
Clothing to cover skin

106

How can we control the number of mosquitos

Avoid standing water/sewage
Introduce predators
Pesticides
Water treatment to kill larvae

107

Name some of the ethical issues with controlling diseases

People unsure about safety of vaccines
Difficult to obtain consent where medical education is little
Money can be spent better elsewhere

108

Name some of the social issues with controlling diseases

People need to change habits
Change social attitudes - difficult

109

Name some of the economic issues with controlling diseases

Treatment, control and prevention is expensive and countries are normally poor
Difficult to allocate resources

110

What is the role of the scientific community in controlling diseases

Prevention: getting insecticide filled nets
Treatment: using drugs in combination is more effective

111

What are antigens?

Any substance that stimulates an immune response from the body

112

What substances can be antigens?

Proteins, glycoproteins, carbohydrates, toxins and even whole organisms

113

What is a non-specific response?

The body's defence against pathogens which is triggered by any pathogen

114

What are the three main types of non-specific response?

Inflammation
Fever
Phagocytosis

115

Explain the stages leading to inflammation

Tissue damage causes mast cells and basophils to release histamines
Blood vessels dilate - local heat and redness to reduce effectiveness of pathogens
Leaky capillaries cause leucocytes to be released and engulf pathogens and antibodies to disable them

116

What are histamines?

Chemicals which cause blood vessels to dilate and cause capillaries to leak

117

Explain why you get a fever while ill

Hypothalamus increases body temperature:
- reduce the effectiveness of pathogens
- immune system works better at a higher temperature

118

What is a phagocyte?

A general term for an WBC that engulfs and digests pathogens any other foreign material in the blood

119

Name the 2 types of phagocytes

Neutrophils and macrophages

120

Name some characteristics of neutrophils

Granulocyte
Can only ingest a few pathogens before it dies
Cannot renew lysosyme stores

121

Name some characteristics of macrophages

Agranulocyte
Made from monocytes from the tissue
Can renew their lysosyme stores

122

Explain how phagocytes work

Engulfs pathogen
Phagosome surrounds pathogen and fuses with lysosom
Enzymes break down pathogen
Cytokines released

123

What do cytokines do?

Signal for other WBCs
Stimulate immune response

124

What are opsonins?

Chemicals which bind to pathogens and label them so WBCs can detect them more easily

125

What is the immune response?

Body's specific response to invasion by pathogens

126

Name the four characteristics of the immune system

Distinguish self from non-self
Diverse
Specific
Immunological memory

127

What are the two main types of WBC in the immune system?

Lymphocyte and macrophage

128

What are the two types of lymphocytes in the immune system?

B lymphocytes
T lymphocytes

129

Name the types of B lymphocytes

B effectors
Plasma cells
B memory

130

Name the types of T lymphocytes

T killer
T helper
T memory

131

Where do B cells get made and develop?

Bone marrow then develop in the lymph gland

132

Where do T cells get made and develop?

Bone marrow then develop in the thymus gland

133

What do plasma cells do?

Produce antibodies

134

What do T killer cells do?

Produce chemicals to kill infected cells

135

What do T helper cells do?

Activate plasma cells and B cell APCs

136

What are the body's two specific responses to infection?

The humoral response and the cell mediated response

137

When is the humoral response activated?

When the antigens of the pathogens are outside of body cells

138

Name the two main stages of the humoral response

T helper activation
B effector stage

139

Summarise the stages of the T helper activation stage

Macrophage engulfs pathogen
Surrounds with phagosome and lysosome
Separates antigen and binds it to MHC
Becomes APC
T cell with complementary receptor binds to antigen
T cell divides and replicates into activated T memory and T helpers

140

Summarise the stages of the effector stage

B cells act as macrophages and become APCs
T helper binds to B cells and releases cytokines
B cells divide into B effector and B memory
B effector --> plasma cell ---> antibodies

141

What is clonal selection?

The selection of cells that carry the right antibody for a specific antigen

142

What are antibodies?

Glycoproteins that are released into circulation and bind to the antigen of pathogens

143

How can antibodies cause pathogen deaths?

1) Agglutination - pathogens clump then get engulfed
2) Opsonisation - acts as an opsonin and signals for phagocytes
3) Neutralisation - neutralises toxins

144

Name adaptations of plasma cells

Hella endoplasmic reticulum
Ribosomes

145

When is the cell mediated response used?

When the pathogen enters the body cells

146

Summarise the stages of the cell mediated response

Body cells acts as an APC
T killer w complementary receptor binds to APC
T helper releases cytokines so T killer rapidly divides
Release enzymes which make pores in membrane so water +ions enter membrane and cause cell to burst
Pathogens destroyed
T memory cells made

147

What is the difference between the response of T memory cells and B memory cells

T memory cells release T killer cells
B memory cells produce antibodies

148

What is the primary immune response?

When the body has come into contact with a pathogen and its antigen for the first time. Involves the production of antibodies and memory cells

149

What is the secondary immune response?

When the body comes into contact with a pathogen again and memory cells are used

150

What is natural active immunity?

When the body produces its own antibodies against a pathogen and its antigen encountered naturally

151

What is natural passive immunity?

When antibodies are made by the mother and passed onto the baby via breastmilk or placenta

152

What is immunisation?

The process of protecting people from infection by giving them passive or active artificial immunity

153

What is a vaccination?

The procedure of giving someone dead or inactive pathogen to stimulate an immune response

154

What is passive artificial immunity?

When the antibodies from one individual are extracted and injected into another

155

What is active artificial immunity?

When the body produces its own antibodies and memory cells to an antigen from a vaccination

156

How is the pathogen in a vaccination made non-infectious?

Toxin detoxified
Inactive/dead pathogen
Attentuated pathogens - viable but modified so they dont cause disease

157

What is the only disease to be eradicated?

Smallpox

158

Why is it not possible to totally eradicate many diseases?

They have multiple hosts - animals, soils and waters

159

What is the elimination of a disease?

Where it is no longer seen in humans but exists in the environment or animal so vaccinations still needed

160

What is meant by a controlled disease?

When a disease is still occurring but not to the extent that it is a health problem

161

Define herd immunity?

When a large proportion of a population is immune to a pathogen (usually by vaccination) which lowers the risk of infection

162

What are the pros of vaccination?

Person is protected against infection - dont die
Herd immunity - those who cant get immunised are still safe
Costs of treating disease minimised

163

What are the cons of vaccination?

Some children cant be vaccinated bc of allergies or extreme immune response

164

Name a bacteria which produces exotoxins

Staphylococcus aureus

165

Name a bacteria which produces endotoxins

Salmonella