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Physiology of Microbes > Selective and Diagnostic Culturing L17 > Flashcards

Selective and Diagnostic Culturing L17 Flashcards

(57 cards)

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1
Q

what is a phototroph

A

organism that is nutritionally able to synthesise all its required growth factors from simple substances

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2
Q

how do substances vary

A

depending on the nutritional classification of the organism

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3
Q

what are physical conditions that should be met

A

Temperature
pH
O2 levels
Osmolarity

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4
Q

what are general nutritional requirements

A 
carbon source
nitrogen source
sodium
phosphorus 
sulphur 
iron
trace elements
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5
Q

what are the carbon sources available for nutrition

A

CO2 (AUTOTROPHS)
Organic molecules (HETEROTROPHS)
e.g. glucose

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6
Q

what are the nitrogen sources available for nutrition

A

inorganic e.g. N2 NH4

organic e.g. amino acids

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7
Q

what is sodium for in nutritional requirement

A

transporters

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8
Q

what are the phosphorus elements in nutritional requirements

A

nucleotides and ATP

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9
Q

what are the sulphur elements in nutritional requirements

A

SOv4^2- sulfate
H2S hydrogen sulphide
as aminoacids (Cys)

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10
Q

what are the iron elements in nutritional requirements

A

(Fe2+): cytochromes, catalase & other enzymes

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11
Q

what are the trace elements in nutritional requirements

A

Zn2+; Cu2+; Mn2+; Mo6+; Co2+

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12
Q

what are the trace elements for in nutritional requirements

A

required for a range of enzyme activities
required at very low levels (mg l-1)
sufficient present as contaminants in most media

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13
Q

what is defined media

A

made from mixtures of pure chemicals and contain precisely controlled amounts of each chemical
requires a thorough knowledge of cell metabolism

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14
Q

what is the growth media prepared as

A

mixtures of extracts:

  • yeast extracts: vitamins and amino acids
  • peptones: amino acids and TE’s from hydrolyzed protein
  • meat infusions: soups
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15
Q

where are peptones produced

A

Peptones are produced from a variety of raw materials

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16
Q

what is the effect of a different growth media

A

end product will contain a different range of aa’s and minerals which favour growth of different organisms

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17
Q

what peptones are from milk

A

casein peptones

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18
Q

what peptones are from meat

A

general peptones

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19
Q

what peptones are from soya

A

plant peptones

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20
Q

what are the methods of isolating a particular organism

A

using

  • selective medis
  • differential medium
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21
Q

what is selective media

A

contains selective agents which prevent growth of some organisms but allows others to grow

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22
Q

what does selective media often contain

A

antibiotics

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23
Q

what does selective media require

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A

requires an understanding of the growth parameters of the whole population

24
Q

what is differential medium

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A

particular organism has a characteristic appearance on the medium

25
which agar is used for staphylococcus aureus
baird parker
26
what does staphylococcus look like on baird parker agar, under what particular conditions
produces grey/black shiny colonies with a clear halo in 24h at 37°C
27
what do other staphylococci look like on baird parker agar
dont produce a clearing
28
what does bacillus look like on baird parker agar
brown, matt colonies
29
what does proteus look like on baird parker agar
produces brown/black colonies
30
what agar is E. coli and Salmonella grown on
MacConkey agar
31
how are E.coli and Salmonella differentiated on agar
pH change (media contains a pH indicator) due to their different ability to ferment lactose
32
what colour does lactose positive turn and which bacteria on what agar
pink E.coli MacConkey
33
what colour is lactose negative
yellow
34
what is bacillus cereus selective agar used for
Precipitates Lecithin in egg yolk | Cannot utilise mannitol so medium stays blue
35
what bacteria grows well on mannitol salt agar, what does the bacteria do
Staphylococcus aureus grows in presence of high salt (S) and ferments mannitol to produce acid (D) agar changes from normal red to yellow
36
what are the three general modes of antibiotic action
1)   prevent synthesis of bacterial cell wall (e.g. all β-lactams) 2)   damage cytoplasmic membrane (e.g. polymxyin) 3)   interfere with biochemical synthesis
37
what does Rifampicin do, where is it used
inhibit transcription | antibiotics - interfere with biochemical syntheis
38
what does Chloramphenicol, Streptomycin, Tetracycline do, where is it used
inhibit ribosome function | antibiotics - interfere with biochemical synthesis
39
what does Fluroquinolones do, where is it used
inhibit DNA replication | antibiotics - interfere with biochemical synthesis
40
what can lead to antibiotic resistance
1)   Absence of a target site 2)   Variants/point mutations in target sites that prevents the antibiotic binding 3) Enzymes to detoxify the antibiotics 4)   Efflux pumps that remove the antibiotic before it damages the cell
41
when are enrichment procedures used
Used where essential to detect very low numbers of a specific organism e.g. food borne pathogens in food samples Also helps to revive damaged cells e.g. those that have survived a processing step or have been in an unfavourable environment and may be sub-lethally injured
42
what is the enrichment procedure steps STEP1
Pre-enrichment increase cells present allows resuscitation/recovery of damaged cells non-selective broth used
43
what is the enrichment procedure steps STEP2
Selective enrichment (broth) promotes desired organism growth prevents/retards growth of other organisms combinations of: substances toxic to unwanted bacteria inhibitory growth conditions conditions increasing growth of target organism
44
what is the enrichment procedure steps STEP3
``` Selective plating (agar) isolates organism of interest on selective /diagnostic agar = presumptive positive ```
45
what is the enrichment procedure steps STEP4
Confirmative tests | further testing is required to confirm identification
46
what are confirmatory tests
1st 2 common tests are Catalase and Oxidase tests
47
what does the catalase test do
detects enzyme that detoxifies Hydrogen peroxide | Typical of obligate aerobes and most facultative anaerobes
48
what does the oxidase test do
detects cytochrome c oxidase | Tells you that organism is able to use oxygen as a terminal electron acceptor
49
what is defined medium
ability to utilise specific sugars or amino acids
50
what is medium containing defined substrates
ability to metabolise specific compounds
51
what is the more common small scale rapid tests
API or Biolog
52
what biochemical tests are carried out by preparing small cultures
defined medium medium containing defined substrates more common to carry out small scale, rapid tests e.g. API or Biolog
53
what is antibiotic testing
serology
54
what happens in antibiotic testing, serology
Agglutination tests carried out using antisera specific for the target organism
55
what does it mean if clumping occurs in serology
cells have cross-reacted with the antibody
56
what DNA based tests detect specific genes
DNA hybridisation methods | PCR amplification of genes
57
how is media prepared
Components of media provided as dry powders - Correct amounts weighed out - Mixed with correct amount of distilled water - Sterilised by autoclaving - Cool and pour into Petri dishes > Before pouring, heat sensitive components can be mixed into the molten agar > Includes many antibiotics, vitamins, proteins, lipids

Physiology of Microbes (21 decks)

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