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A Level Biology > Topic 6.1- Bacteria and disease > Flashcards

Topic 6.1- Bacteria and disease Flashcards

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1
Q

Why are aseptic techniques important when culturing microorganisms?

A

to produce uncontaminated culture so results are reliable + repeatable

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2
Q

List the basic aseptic techniques

A
  • wipe surfaces with antibacterial wipes/cleaner
  • set up Bunsen burner nearby. Convention currents prevent microbes from entering culture
  • flame inoculating loop + neck of bottles before use
  • minimise time that vessels containing bacteria are open
  • sterilise all equipment e.g. using an autoclave
  • wear protective clothing
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3
Q

Outline how to culture microorganisms

A
  1. Transfer bacteria to agar plate using sterile inoculating loop or pipette
  2. Tape lid on at 2 ends then invert the dish and incubate. In school labs ensure that dish isn’t airtight + do not incubate above 25 degrees to avoid growth of pathogen
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4
Q

Explain the difference between a streak plate and a spread plate

A
  • streak plate: aims to obtain single colonies by rotating the plate to build layers of the culture on at least 3 separate streaks
  • spread plate: aims to distribute microorganisms evenly with a sterile spreader
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5
Q

Describe the 3 types of nutrient medium

A

-liquid broth
-solid agar
(usually contain nitrogen, carbon, + minerals, often enriched with protein from extract of yeast, blood or meat)
-selective mediums (contain highly specific nutrient balance, only certain microorganisms grow)

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6
Q

Give the advantages of using a broth medium

A
  • can provide anoxic + oxic conditions depending on depth, which helps to identify microbes/ determine their optimum conditions
  • can grow a very large quantity of bacteria
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7
Q

Give the advantage of using agar as the medium

A

can obtain single, discrete pure colony for study

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8
Q

Name the 4 phases of the bacterial growth curve

A
  1. lag phase
  2. log phase
  3. stationary phase
  4. death phase
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9
Q

What happens during the lag phase?

A

microorganisms need to adjust to the environment before reproducing so population size only increases slowly

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10
Q

What happens during the log phase?

A

after every round of division population size doubles (exponential growth)

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11
Q

What happens during the stationary phase?

A

reproduction rate= death rate, so population size stabilises at its max

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12
Q

What happens during the death phase?

A

microorganisms die due to build up of toxic waste products + lack of nutrients

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13
Q

Name 3 methods used to estimate the growth of a bacterial culture

A
  • cell count
  • turbidity measurement (type of colorimetry to measure opacity)
  • dilution plating
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14
Q

Explain how to conduct a cell count

A
  1. dilute broth sample with equal volume of trypan blue to stain dead cells blue
  2. use a calibrated haemocytometer with volume 0.1mm3. Count the cells in each of the sets of squares and calculate the mean
  3. number of bacterial cells = counted number x10^4 per cm3
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15
Q

Suggest advantages and disadvantages of using a cell count

A

advantage: only counts living cells
disadvantages:
- slow
- expensive equipment
- large margin for human error

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16
Q

Explain how to conduct a turbidity measurement

A
  1. use colorimetry. measure absorbance or % transmission of samples with known microorganism count
  2. plot calibration curve: absorbance/ % transmission (y-axis) number of microorganisms (x-axis)
  3. record absorbance/ % transmission of unknown sample
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17
Q

Suggest advantages and disadvantages of using a turbidity measurement

A

advantages:
-quick
-can be conducted in the field
disadvantages:
-counts both living and dead cells
-requires calibration curve from known samples
-assumes equal density of cells across culture

18
Q

Explain how to conduct dilution plating

A
  1. grow a colony from a single microorganism
  2. perform serial dilution with distilled to see single colonies
  3. prepare a lawn plate and count colonies
  4. number of cells= number of colonies x dilution factor
19
Q

What are endotoxins?

A

lipopolysaccharides that are an integral part of the outer layer of the cell wall of Gram-negative player

20
Q

What are exotoxins?

A

soluble proteins that are produced and released into the body by bacteria as they metabolise and reproduce in the cells of their host

21
Q

Define lipopolysaccharides

A

large molecules containing a lipid element and a polysaccharide element

22
Q

What is tuberculosis?

A

a lung disease caused by Mycobacterium tuberculosis and M.bovis

23
Q

What’s the primary infection of tuberculosis?

A

the initial stage of tuberculosis when M.tuberculosis has been inhaled into the lungs, invaded the cells of the lungs and multiplies slowly, showing no obvious symptoms

24
Q

What is a tubercle?

A

the result of a healthy immune response to an infection by M.tuberculosis. a localised inflammatory response forms a mass of tissue containing dead bacteria and macrophages

25
Q

What adaptation does Mycobacterium tuberculosis have?

A

it can avoid the immune system, allowing some bacteria to survive the primary infection stage. they produce a thick, waxy outer layer which protects them from macrophage enzymes- this means they can remain deep in the tubercles in the lungs (dormant or growing slowly)

26
Q

What makes dormant or slowly growing tuberculosis bacteria active?

A

when the person becomes malnourished, weakened or their immune system doesn’t work well. these bacteria can then cause active tuberculosis

27
Q

Define an antibiotic

A

a drug that either destroys microorganisms or prevents them from growing and reproducing

28
Q

What is selective toxicity?

A

a substance is toxic against some types of cells or organism but not others

29
Q

What is penicillin?

A

the first antibiotic discovered. affects the formation of bacterial cell walls and is bactericidal

30
Q

What are bactericidal antibiotics?

A

kill bacteria

31
Q

What is meant by bacteriostatic antibiotics?

A

inhibit the growth of bacteria

32
Q

What’s tetracycline?

A

a bacteriostatic antibiotic that inhibits proteins

33
Q

Define an antibiotic-resistant organism

A

not affected by an antibiotic even if it was effective in the past

34
Q

What factors determine the effectiveness of an antimicrobial drug?

A
  • the concentration of the drug in the area of the body infected (affected by how easily the drug can affect the tissue and how quickly it’s excreted)
  • the local pH
  • whether the pathogen or the host tissue destroy the antibiotic
  • the susceptibility of the pathogen to the particular antibiotic used
35
Q

How are bacteria harmful?

A
  • produce exotoxins
  • endotoxins are surface trigger immune response
  • invade and destroy host tissues
36
Q

How does Salmonella spp. cause disease?

A
  • Gram negative bacterium with polysaccharide endotoxins on outer membrane, triggers release of cytokines
  • acute inflammation results in diarrhoea
  • releases toxins into the host when bacterium dies
37
Q

How does Staphylococcus spp. cause disease?

A

secretes exotoxins (soluble proteins)

  • barrel shaped proteins embed in host cell membrane so contents leak
  • protease toxins
  • superantigens trigger 20% of T cells so can cause toxic shock
38
Q

How does Mycobacterium tuberculosis cause disease?

A
  1. triggers inflammatory response by infecting phagocytes in the lungs
  2. infected phagocytes are sealed in waxy-coated tubercles so bacteria remain dormant. first infection is symptomless
  3. if another factor weakens immune system, bacteria become active and destroy lung tissue
39
Q

How does penicillin work?

A

beta-lactam bactericidal antibiotic prevents formation of the peptidoglycan cross-links in cell wall, causing osmotic lysis

40
Q

How does tetracycline work?

A

bacteriostatic antibiotic, prevents protein synthesis by binding to small subunit of ribosome so tRNA cannot attach. therefore inhibits growth and division
(bacteriostatic antibiotics may also inhibit nucleic acid formation)

41
Q

What causes antibiotic resistance?

A
  • random genetic mutation, often plasmid e.g. antigen change shape
  • these bacteria have selective advantage in the presence of antibiotics
  • reproduce and pass on allele for resistance to offspring
  • directional selection causes resistant strain
42
Q

How do hospitals minimise the spread of antibiotic resistant bacteria?

A
  • screening and quarantining of sick patients
  • hygiene code of practice e.g. alcohol-based wipes, gels
  • antibiotics prescribed only when necessary and course completed to minimise selection pressure

A Level Biology (32 decks)

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