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MDL 251 Unit 2 > Tests > Flashcards

Tests Flashcards

1
Q

Principle of Catalase

A

get rid of the peroxide in a cell

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2
Q

Positive results of catalase

A

immediate appearance of bubbles

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3
Q

Negative result of catalase

A

no or few bubbles after 20 sec

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4
Q

Errors with catalase

A

Picking up blood agar with colony. RBC produce catalase and may give a false positive

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5
Q

Catalase procedure

A
  1. Remove colony from blood or chocolate plate with wooden stick.
  2. Apply to dry glass slide
  3. Add 1 drop of 3% hydrogen peroxide (H2)2) to drop
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6
Q

What does catalase test differentiate?

A

Differentiates between Staph (positive) from Strep (negative). Enterococcus can produce a pseudocatalase result

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7
Q

Principle of coagulase

A

identifies whether an organism produces the exoenzyme coagulase, which causes the fibrin of blood plasma to clot

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8
Q

Positive result of coagulase

A

clot of any size

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9
Q

Negative result of coagulase

A

no clot

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10
Q

Slide Coagulase Procedure

A
  1. Place a drop of coagulase on one side of slide with a drop of saline/water on the opposite
  2. Remove a colony from plate using a loop or stick and mix in saline/water
  3. Remove a separate colony from plate and mix with coagulase serum
  4. Rock slide for 5-10 seconds.
  5. Within 10 seconds clumps will appear if positive.
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11
Q

Tube Coagulase Procedure

A
  1. Add several colonies from plate with loop to coagulase serum in test tube
  2. Incubate at 35°C for up to 4 hours
  3. Check for clotting during incubation
  4. If no clots incubate for 24 hours and recheck
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12
Q

Principle of staph latex agglutination

A

detects both clumping factor and protein A, which are used to distinguish S. aureus from other staphylococcus species

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13
Q

Positive results of staph latex agglutination

A

large black clumps of agglutination with loss of black background

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14
Q

Negative results of staph latex agglutination

A

little or no agglutination (without loss of black background)

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15
Q

staph latex agglutination Procedure

A
  1. Pretest colonies with gram stain and catalase.
  2. Warm reagents to room temperatiure
  3. Mix latex reagent by mixing
  4. Use dropper to dispense one drop of reagent onto the test slide
  5. Select 2-5 isolated colonies from an 18-24 hour culture to dry area inside circle
  6. Slowly blend the staphylococcus into the reagent using the stick
  7. Spread mixure over the entire area of the circle
  8. Circulate the slide for up to 60 seconds
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16
Q

Microdase principle

A

differentiates staphylococcus from micrococcus

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17
Q

Positive Microdase

A

blue or purple-blue color development within 2 minutes

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18
Q

Negative Microdase

A

no color change within 2 minutes

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19
Q

Microdase procedure

A
  1. Test should be performed on aerobic, catalase +, gram pos cocci. Colonies should be from a blood agar <24 hours.
  2. Place disk on clean glass slide using forceps
  3. Use wooden stick to inoculate the disk with several well isolated colonies.
  4. Examine for up to 2 minutes for blue color development
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20
Q

Optochin Principle

A

determines the effect of optochin on an organism. Pneumococci will be lysed but other alpha streptococci will not.

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21
Q

Optochin Positive Result

A

Zone is ≥ 14mm

22
Q

Optochin Negative Result

A

No zone

23
Q

Optochin Equivocal

A

Zone is < 14mm. Questionable, perform bile solubility

24
Q

Optochin Procedure

A
  1. Streak colonies onto SBA
  2. Place optochin disk in upper third of streaked area
  3. Incubate at 35° in 5% CO2
  4. Measure zones of inhibition
25
Q

Bile Solubility Principle

A

differentiates S. pneumonia from alpha hemolytic streptococci

26
Q

Bile Solubility Positive

A

colony disintegrates; an imprint of the lysed colony may remain in the zone

27
Q

Bile Solubility Negative

A

intact colony

28
Q

Bile Solubility Procedure

A
  1. After 12-24 hours incubation on SPA, place 1-2 drops of 10% sodium desoxycholate on a well isoled colony
  2. Gently wash liquid over the colony without dislodging the colony from the agar
  3. Incubate the plate at 35°-37°C in ambient air for 30 minutes
  4. Examine for lysis of colony
29
Q

Bile Solubility Errors

A

Because of nutritional requirements, some organisms may grow poorly or not at all on this media

30
Q

Salt Tolerance Test Principle

A

determines ability of an organism to tolerate high salt concentrations. Differentiates enterococci from non enterococci

31
Q

Salt Tolerance Test Positive

A

Visible turbidity in broth with or without a color change

32
Q

Salt Tolerance Test Negative

A

No turbidity or color change

33
Q

Salt Tolerance Procedure

A
  1. Inoculate 1-2 colonies from 18-24 hr culture into 6.5% salt tube
  2. Incubate for 24-48 hours at 35°C
  3. Check daily for growth
34
Q

CAMP test Principle

A

differentiate group B streptococci from other streptococcal species

35
Q

CAMP test Positive

A

Enhanced hemolysis in the shape of an arrowhead

36
Q

CAMP test Negative

A

No enhanced hemolysis

37
Q

CAMP test Procedure

A
  1. Streak a beta hemolytic S. aureus down the center of a SBA plate
  2. Streak test organisms perpendicular to the S. aureus streak
  3. Incubate overnight
38
Q

CAMP test errors

A

Small percentage of group A streptococci may have a positive CAMP. Limit test to colonies with characteristic group B strep morphology

39
Q

Motility (Listeria) Principle

A

determines if an enteric organism is motile. Organism must have flagella to be motile

40
Q

Motility Positive

A

organisms will spread out into the medium from the site of inoculation

41
Q

Motility Negative

A

organisms will remain at the site of inoculation

42
Q

Motility Procedure

A
  1. Touch a straight needle to a colony of a young culture on agar medium
  2. Stab once to a depth of 1/3 to ½ inch in the middle of the tube
  3. Incubate and examine daily for up to 7 days
43
Q

Motility Errors:

A

some organisms will not display sufficient growth in the medium to make an accurate determination. Followup test may be required

44
Q

PYR Principle

A

presumptive ID of group A streptococci

45
Q

PYR Positive

A

Bright red color within 5 minutes

46
Q

PYR Negative

A

No color change or an orange color

47
Q

PYR Procedure

A
  1. Moisten disk without flooding
  2. Use a wooden stick to put colonies on the PYR disk
  3. Incubate at room temp for 2 minutes
  4. Add a drop of detector and observe for a red color within 1 minute
48
Q

Lancefield Grouping Principle

A

identify beta hemolytic streptococci into a lancefield group. Specific antibodies on latex particles react with and agglutinates

49
Q

Lancefield Grouping Positive

A

2+ or greater reaction observed within 60 seconds

50
Q

Lancefield Grouping Negative

A

A uniform or milky appearance with no agglutination

51
Q

Lancefield Grouping Procedure

A
  1. Pick 3-4 colonies from SBA plate
  2. Rub the colonies on the slide in oval
  3. Add a drop of latex A to oval and mix with stick
  4. Repeat for latex B, C, F, or G
  5. Rock slides back and forth for up to a minute. Observe for agglutination

MDL 251 Unit 2 (3 decks)

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