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Diagnostic Microbiology > Biochemical Tests > Flashcards

Biochemical Tests Flashcards

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1
Q

what does the bile solubility test differentiate between

A

differentiates between Streptococcus pneumoniae (positive) and other alpha-haemolytic streptococci

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2
Q

what indicates a positive result in the bile solubility test

A

colony soluble = positive

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3
Q

what does catalase production test differentiate between

A

differentiates between staphylococci (positive) and streptococci (negative)

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4
Q

what indicates a positive and negative result in the catalase production test

A

Gas bubbles produced = positive

no gas produced = negative

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5
Q

what is the principle behind the catalase test

A

presence of catalase enzyme enables the ability to decompose hydrogen peroxide, liberating oxygen gas
present in most aerobic cells except streptococci

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6
Q

what is the citrate utilisation test used for

A

to differentiate coliform organisms

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7
Q

what is the principle behind the citrate utilisation test

A

determines if an organisms can use citrate as the sole source of carbon
organism is inoculated on Simmons citrate agar slope
positive result; growth on plate, slope turns from green to blue or yellow

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8
Q

what indicates a positive and negative result in the citrate utilisation test

A

growth on Simmons citrate agar = positive

no growth = negative

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9
Q

what is the principle behind the coagulase test

A

coagulase in an enzyme that converts fibrinogen into fibrin
resulting in clot formation
test indicates the ability of an organism to clot plasma using the coagulase enzyme

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10
Q

what is coagulase test differentiate between

A

differentiates between Staphylococcus sp.
Staphylococcus aureus = usually positive
Staphylococcus epidermidis = negative

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11
Q

what indicates a positive and negative result in the coagulase test

A

positive: large irregular clumping after 1 min
negative: no organism clumping after 1 min

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12
Q

what should the control show in a coagulase test

A

control should show thoroughly dispersed organisms with no clumping

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13
Q

what does the germ tube test differentiate between

A

differentiates Candida albicans from other yeasts

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14
Q

explain the principle behind the germ tube test

A

inoculate a colony of yeast in horse serum for 2-3hrs
examine microscopically, positive result (C. albicans) shows hyphal extension arising laterally from yeast cells (germ tube)

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15
Q

what does the indole production test for

A 
bacteria that produce tryptophanase enzyme 
cleaves tryptophan (producing indole) 
indole production can be detected by development of a red colour in the presence of Kovac's reagent
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16
Q

what indicates a positive and negative result in the indole production test

A

positive: red colour
negative: no colour change

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17
Q

what is the Nagler reaction used for

A

used to identify Clostridium perfringes

tests for the ability of an organisms to produce lecithinase

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18
Q

what is the principle behind the optochin disc test

A

determines organisms susceptibility to optochin

19
Q

what does the optochin disc test differentiate between

A

differentiates between Streptococcus pneumoniae (sensitive) and other alpha-haemolhytic streptococci

20
Q

what tests could be used to differentiate between Streptococcus and other alpha-haemolytic streptococci

A

bile solubility test or optochin disc test

21
Q

what indicates a sensitive and resistant result using the optochin test

A

sensitive: clear zone around disc, Strep. pneumoniae have a zone size of 14-16mm or greater around the disc
resistant: no zone or small zone, indicates its not Strep. pneumoniae

22
Q

what is the principle behind the oxidase test

A

tests for the presence of oxidase enzymes in the cell

23
Q

what bacteria are oxidase positive

A
  • Neiserria sp
  • Vibrio cholerae
  • Bacillus anthracis
  • Bacillus subtilis
  • Pseudomonas aeruginosa
24
Q

what indicates a positive and negative result using the oxidase test

A

positive; dark purple streak on filter paper impregnated with oxidase reagent after 5-10 sec (smear has been oxidised by bacterial oxidases
negative: no colour change within seconds

25
Q

what is the modified oxidase test used for

A

to differentiate between Staphylococcus and micrococcus
positive = purple colour change after 2 mins (Staph)
negative = no colour change (micrococcus)

26
Q

what is the sugar utilisation tube test used for

A

differentiate between Neisseria species based on their carbohydrate fermentation patterns

27
Q

what indicates a positive result in the sugar utilisation test

A

positive = colour change to yellow

28
Q

what sugars are involved in the sugar utilisation test

A

Glucose, lactose, maltose and sucrose

ability to utilise a combination of these gives Neisseria species identification

29
Q

what is the superoxol test and what organism is it used for

A

catalase test used for the identification of Neisseria gonorrhoeae

30
Q

what is the urease production test used for

A

used to differentiate Proteus (urease positive) from other members of the Enterobacteriaceae

31
Q

name 2 organisms which are urease positive

A

Proteus and Klebsiella

32
Q

name 2 organisms which are urease negative

A

Escherichia and Providencia

33
Q

How is the VP (Voges-Proskauer) test used

A

usually done in conjunction with methyl red test

34
Q

what is the VP (Voges-Proskauer) test used for

A

separate E. coli from the Klebsiella-Enterobacter groups

35
Q

what indicates a positive result using the VP (Voges-Proskauer) test

A

positive: bright cherry red colour after 5-15 mins which fades after an hr

36
Q

what does the X and V test differentiate between

A

differentiates between different Haemophilus species

37
Q

what is the principle of the X and V test

A

X, V and XV discs are placed onto agar surface
organisms require either X, V or both factors in order to grow
organisms will only grow around the disc that have the factor(s) that they require

38
Q

which organisms grow around X and XV discs

A

Haemophilus ducreyi

39
Q

which organism grow only around XV discs

A

Haemophilus influenzae and Haemophilus haemolyticus

40
Q

which organisms grow around V and XV discs

A

Haemophilus parainfluenzae and Haemophilus parahaemolyticus

41
Q

what organisms can be identified using the API20E test

A

identify enteric and other Gram negative bacteria

42
Q

what organisms can be identified using the API2ONE test

A

identify non-fastidious, non-enteric GNB

e.g. Pseudomonas, Acinetobacter, Flavobacterium, Moraxella, Vibrio, Aeromonas

43
Q

what organisms can be identified using the API NH test

A

used to identify Neisseria and Haemophilus sp.

44
Q

what is the Kirby-bauer disc diffusion test used for and how does it work

A

determine susceptibility of bacteria to antimicrobial compounds
uses MHA inoculated with diluted bacterial suspension (0.5 McFarland)
antibiotic impregnated discs are added to the plate and incubated, zones of inhibition measured to determine susceptibility

Diagnostic Microbiology (2 decks)

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