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Microorganisms + Disease > Practicals > Flashcards

Practicals Flashcards

1
Q

what happens in the catalase test

A

catalase enzyme catalyses the dissociation of hydrogen peroxide to oxygen and water

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2
Q

what bacterias are catalase positive

A

staphylococci
corynebacteria
bacillus

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3
Q

what bacterias are catalase negative

A

streptococci
lactobacilli
clostridium

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4
Q

what is the procedure of the catalase test

A

pick a colony of chosen microbe, smear over clean glass slide, place a drop of hydrogen peroxide onto this smear

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5
Q

what shows a positive catalase test

A

organisms will fizz

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6
Q

what is the problems with catalase test

A

hydrogen peroxide is corrosive and oxidising

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7
Q

what happens in the oxidase test

A

detects enzyme cytochrome C oxidase, more discriminatory for Gram-negative than Gram-positive bacteria

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8
Q

what is an example of enterobacteriaceae

A

E. coli

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9
Q

what is the oxidase test good for distinguishing species

A

particularly useful for distinguishing species of Pseudomonas and Vibrio from members of Enterobacteriaceae

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10
Q

what is the procedure for the oxidase test

A

use plastic loop, get colony from plate, smear lightly on strip of filter paper impregnated with oxidase reagent, denoted by development of deep purple colour, will occur in 15 seconds

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11
Q

what happens if colour develops after 15 seconds

A

after a long period should be ignored

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12
Q

what happens in the coagulase test

A

Staphylococcus aureus has the useful differential characteristic of coagulating plasma whereas the related Staphylococcus epidermis lacks this property

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13
Q

what the procedure for the coagulase test

A

loop to place 2 separate drops of saline on microscope slide
remove 2 or 3 colonies of test organism with loop and gently rub into each drop of saline, form creamy suspension
add loopful of plasma to one of the bacteria suspensions
new loop, loopful of saline to the other
mix gently by rocking the slide, if coagulase positive, bacteria will quickly clump to give speckled granular appearance

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14
Q

what is the second suspension for in the coagulase test

A

serves as a saline control to check for auto-agglutination

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15
Q

what happens in the DNAse agar test

A

Staphylococcus aureus produces a deoxyribose whereas coagulase-negative staphylococci do not
distinguishing characteristic can therefore be tested

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16
Q

what is the procedure of the DNAse test

A

loop to get colony of test organism and stab inoculate Aa DNAse plate (puncture agar)
inoculate plate with control Staphylococcus epidermis, space between the two inoculations
incubate 37degrees C overnight
flood plate with concentrated hydrochloric acid and examine clearing zones of inoculation sites

17
Q

what is the problem with DNAse test

A

hydrochloric acid is corrosive

18
Q

how is streptococci identified

A

method uses Prolex Streptococcal grouping latex kit, provides most rapid serological identification of groups A, B, C, D, F and G Lancefield groups of streptococci grown on agar plates

19
Q

what is the procedure to identify streptococci

A

add 1 drop of reagent to round bottom tube
pick complete isolated beta-haemolytic colony from streptococcal-selective plate gently mix with reagent 1, ensure turbid solution
add 1 drop of reagent 2 to tube, gently mix
add 5 drops of reagent 3 to tube, gently mix
label cards A, B, C, D, F, G dispense drop of each specific latex suspension, mix with loops
group Streptococci

20
Q

what is a problem with Streptococci grouping

A

take care when preparing suspensions of bacteria to avoid generating aerosols

21
Q

what happens in the API test

A

differentiation between gram-negative enteric bacteria based on variable abilities to metabolise selection of biochemical substrates
substrates are provided in test strip, after addition of test bacterium, overnight incubation, results are scored, used to generate a numerical identifier

22
Q

what is the procedure of the API test

A

inoculate tube of distilled water with loop of organism
gently homogenise solution with sterile Pasteur pipette
inoculate bacterial suspension into each well with sterile pipette used to homogenise above
incubate strip at 37degrees C for 18-24hrs
add appropriate reagents
interpret results of test

23
Q

what is a problem of API test

A

when preparing suspension of bacteria to avoid generating aerosols

24
Q

which bacteria are bacilli

A 
E.coli
P.aeruginosa
C.perfringens
B.cereus
S.typhimurium
25
Q

what bacteria are cocci

A

S.aureus

S.pyogenes

26
Q

what is a strict anaerobe

A

will only grow in complete absence of oxygen

27
Q

what is a strict aerobe

A

can only grow when oxygen present

28
Q

what is a facultative anaerobe

A

prefer aerobic conditions but can also grow aerobically

29
Q

what is indicated if bacteria grow on MacConkeys agar

A

bile tolerant as agar contains bile
also contains lactose, bacteria can use this lactose to grow and form bright red colonies = lactose fermentation
if not red then no lactose fermentation

30
Q

what is MacConkeys agar used for

A

indicator medium

31
Q

what does oxolinic acid do

A

chemotherapeutic agent will inhibit the growth of most gram-positive bacteria, much less inhibitory to streptococci than other species

32
Q

what is COBA

A

colistin oxolinic acid blood agar

33
Q

what does COBA agar growth show

A

used to selectively isolate streptococci bacteria
Colistin inhibits the growth of gram negative bacterias
Oxolinic acid inhibits the growth of most Gram positive bacteria other than Streptococci

34
Q

how is enterobacteriaceae be identified

A

API strips, biochemical activities

35
Q

antibiotic sensitivity tests examples

A
  • diffusion tests
  • broth dilution
  • agar dilution tests

Microorganisms + Disease (16 decks)

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