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Cells to Organisms - Practicals > Practical 1. Differentiation of Bacteria and the Induction of Bacterial Gene Expression During Infection > Flashcards

Practical 1. Differentiation of Bacteria and the Induction of Bacterial Gene Expression During Infection Flashcards

1
Q

How can a rough phenotypic differentiation of bacteria be obtained ?

A
  1. The source of bacteria
  2. Cell shape and colony colour and morphology
  3. Gram status
  4. Metabolic features
  5. Phenotypic tests for presence of characteristic genes
    6.
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2
Q

What test will identify if a bacteria is gram positive or gram negative ?

A

The potassium hydroxide test

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3
Q

What can potassium hydroxide do to bacteria ?

A

Quickly lyse gram negative cells as they have a weaker cell envelope and liberate DNA

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4
Q

What do gram positive cells have ?

A
  1. Wall technoic acids
  2. Lipotechnoic acids
  3. Capsular protein
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5
Q

What do gram negative cells have ?

A
  1. Lipopolysaharide
  2. Outer membrane
  3. Periplasm
  4. Outer membrane protein
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6
Q

What is the composition of LPS ?

A
  1. O-antigen
  2. Core saccharide
  3. Lipid A
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7
Q

What does a gram negative bacteria result of a potassium hydroxide test ?

A

Slimy stringy substance

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8
Q

What may gram negative bacteria be further characterised by ?

A

Whether they possess the ability to grow in the presence or absence of oxygen

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9
Q

What is the test used to show the presence of oxygen in gram negative bacteria ?

A

Oxidative fermentative test

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10
Q

What is used to seal the test tube in the oxidative fermentative test ?

A

Paraffin

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11
Q

What does paraffin prevent ?

A

Gas exchange with the environment

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12
Q

What does the growth medium in the oxidative fermentative test contain ?

A

A pH indicator

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13
Q

What will the pH indicator in the growth medium in the oxidative fermentative test do when bacteria have acidified/presence of oxygen ?

A

Will turn the colour of the growth medium yellow

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14
Q

What is the oxidase test used for ?

A

If a bacterium possesses certain cytochrome c oxidases

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15
Q

What does the possession of certain cytochrome c oxidases mean for bacteria ?

A

They can utilise oxygen for energy production via an electron transport chain

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16
Q

What does the oxidase test use as a redox indicator ?

A

N,N,N’,N’-tetramethyl-p-phenylenediamine (TMPD)

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17
Q

What happens when the reagent is oxidised is the oxidase test ?

A

Becomes dark blue

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18
Q

What colour is the reagent in the oxidase test in its initial reduced state ?

A

Colourless

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19
Q

What are many gram negative pathogens ?

A

Oxidase positive

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20
Q

What are some examples of gram negative, oxidase positive bacteria ?

A
  1. Pseudomonas aeruginosa
  2. Helicobacter pylori
  3. Vibrio cholera
  4. Campylobacter jejuni
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21
Q

What does the oxidase test show about the Enterobacteriaceae ?

A

They are oxidase negative

22
Q

What do the results of the oxidase test show about staphylococci and streptococci ?

A

Oxidase negative

23
Q

What will the catalase test do ?

A

Distinguish gram positive bacteria

24
Q

What do most obligate aerobic and faculative anaerobic bacteria produce ?

A

Hydrogen peroxide as an oxidative end product of the aerobic breakdown of sugars

25
Q

What do bacteria do to protect themselves from the toxic hydrogen peroxide ?

A

Produces catalase which converts hydrogen peroxide to harmless water and oxygen

26
Q

What do you see if a bacteria possesses catalase ?

A

Bubbles of oxygen

27
Q

What do bacterial infections occurring via the oral route involve ?

A

Bacteria passing through the stomach prior to entering the intestinal tract

28
Q

What about the stomach kills most bacteria ?

A

The low pH (1.5-3.5)

29
Q

What have bacteria like salmonella enterica serovar typhimurium evolved ?

A

The ability to survive acidic conditions for long enough to reach the intestine

30
Q

What is the asr gene ?

A

highly acid-inducible and is up regulated during salmonella infection

31
Q

What does the asr gene encode ?

A

A small basic periplasmic protein of 102 amino acids

32
Q

What is the small basic periplasmic protein that the asr gene encodes required for ?

A

Growth of bacteria under acidic conditions

33
Q

Where is the asr gene highly expressed ?

A

During the growth at acidic pH 4.5 and 4.0

34
Q

What does the asr mRNA indicate ?

A

asr gene is not highly expressed at pH of 7.2 or 5.0

35
Q

What have genetic tools been developed for ?

A

To enable scientists to visualise when a gene is expressed

36
Q

What is a commonly used genetic tool ?

A

Green fluorescent protein

37
Q

What were E.coli cells transformed with ?

A

A plasmid carrying the genetic reporter

38
Q

What does the this plasmid carry ?

A

A genetic fusion between the aid responsive promoter of the asr gene of salmonella enterica

39
Q

What does the genetic fusion between the acid-responsive promoter of the asr gene of salmonella control ?

A

The expression of the asr gene and the gene encoding green fluorescent protein

40
Q

What happens when transcription is initiated from the asr promoter in response to acidic conditions ?

A

mRNA is transcribed from the downstream green fluorescent protein gene

41
Q

What does the translation of green fluorescent protein mRNA lead to ?

A

Production of the fluorescent green fluorescent protien

42
Q

What does the production of the fluorescent green fluorescent protein make ?

A

The bacteria fluoresce when exposed to light of the appropriate wavelength

43
Q

What does the excitation of the green fluorescent protein protein with blue light lead to ?

A

The generation of green fluorescence

44
Q

What does the origin of replication on plasmid required for ?

A

Maintenance and replication of the plasmid

45
Q

What does the beta lactamase encoding gene provide the bacteria with ?

A

Ampicillin resistance

46
Q

What is ampicillin ?

A

A beta lactam antibiotic

47
Q

What is the beta lactamase encoding gene required for ?

A

To select for cells that carry the plasmid and for plasmid maintenance

48
Q

What is the potassium hydroxide test an alternative to ?

A

Gram staining

49
Q

What are some shapes of bacteria ?

A
  1. Coccus
  2. Coccoid
  3. Rod
  4. Comma shaped
  5. Spirillum
  6. Club shaped
  7. Rod with spore
50
Q

How many genes does salmonella have ?

A

4500

51
Q

How many salmonella genes can change in a few minutes to react to a new environment ?

A

Hundreds

Cells to Organisms - Practicals (4 decks)

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