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Clinical Bacteriology > (M) Lesson 7.1: Gram Positive and Gram Negative Cocci > Flashcards

(M) Lesson 7.1: Gram Positive and Gram Negative Cocci Flashcards

Overview and Different Tests

1
Q

Most commonly received test request in the lab

A

Culture and Sensitivity

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2
Q

Upon receiving this type, you are going to ____ and at the same time perform a ____ on the submitted sample

A

To culture and perform a sensitivity assay

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3
Q
  • Genus and species
  • What bacteria causes the infection
A

Culture

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4
Q
  • The most effective or appropriate antimicrobial agent for the patient to avoid the possibility of having resistance
A

Sensitivity

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5
Q
  • What is the correct dosage or amount
  • Specific antibiotic if bacteria is the suspected case
A

Sensitivity

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6
Q

What is the first thing a lab should do when receiving a wound discharge?

A

Perform a G/S procedure even if not stated in the request

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7
Q

T or F: All samples received in the microbiology lab including stool should be gram-stained.

A

F (not including stool)

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8
Q

Most common G/S result under a microscope

Sample is from an infective suppurative suture

A

Gram-positive cocci in clusters

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9
Q

Wound discharges originating from suppurative lesions to result in ____ because the causative agent of the said infection is the most common cause of infection on a suppurative lesion area.

A

Gram-positive cocci

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10
Q

After seeing the G/S result, the next step should be based on what?

A

Results of the G/S

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11
Q

Upon seeing the G/S results, we should ____ the organism

A

Culture the organism

Inoculate on a plate or culture medium

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12
Q

What are the four routinely used media culture?

A
  1. Blood Agar Plate (BAP)
  2. Chocolate Agar Plate (CAP)
  3. MacConkey Medium
  4. TCBS Media
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13
Q

The selection of culture medium will be dependent on what?

A

G/S Result

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14
Q
  • A general culture medium that is for both gram-positive and gram-negative organisms
  • The best medium for gram-positive cocci
A

Blood Agar Plate (BAP)

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15
Q
  • Used for gram-negative cocci or the physician suspects Haemophilus genus
  • Also routinely used for CSF
A

Chocolate Agar Plate (CAP)

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16
Q
  • Used if gram-negative bacilli is observed
  • Also used for stool specimen
A

MacConkey Medium (MAC)

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17
Q
  • For gram-negative bacilli
  • Stool is suspected of vibrio
A

TCBS Media

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18
Q

____ and ____ are routinely used for fecal samples even if not stated on the test request.

A

MacConkey and TCBS

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19
Q

This is done to get isolated growth of the colony.

inoculation method

A

Overlapping Method

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20
Q

Give the optimal conditions for each category.

Temperature

A

35 to 37°C

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21
Q

Give the optimal conditions for each category.

Duration

A
  • BAP: 24 hours
  • Selective Medium: 48 hours
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22
Q

Give the optimal conditions for each category.

Environment

A

CO2 and ambient air

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23
Q

If general media is used, ____ is the routine incubation time.

A

24 hours

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24
Q

Selective media includes?

A
  1. CAP
  2. MAC
  3. TCBS
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25
Q

Why do we collect isolated colonies?

A

To determine the genus and species

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26
Q

Follow-up tests for biochemical testing will be based on what?

A

G/S results

27
Q
  • First test done on gram-positive cocci
  • Determines the genus
  • Differentiates the two most medically important gram-positive cocci genus in microbiology
A

Catalase Test

28
Q

What are the two most medically important gram-positive cocci genus in microbiology?

A

Staphylococcus and Streptococcus

29
Q

The characteristic arrangement of Staphylococcus?

A

In clusters

30
Q

Catalase Test (Staphylococcus)

Releases ____ enzyme that reacts with ____ to produce free oxygen and water

A

Releases catalase enzyme that reacts with 3% H2O2 to produce free oxygen and water

31
Q

Catalase Test (Staphylococcus)

Releases catalase enzyme that reacts with 3% H2O2 to produce ____ and ____

A

Free oxygen and water

32
Q

Catalase Test

Positive result is?

A

Bubble formation (effervescence)

33
Q

Catalase test

Negative result is?

A

No bubble formation

34
Q
  • There is no bubble formation in catalase test for this organism
  • Requires more follow-up tests
A

Streptococcus

35
Q
  • This test determines the species
  • Serves as a follow-up for catalase based on the importance of the species identified
A

Coagulase test

36
Q

Coagulase Test

____ enzyme is released by a Staphylococcus specie that can clot plasma.

A

Coagulase

37
Q

Coagulase Test

Uses Rabbit’s plasma either in a ____ or ____

A

Citrated or EDTA

38
Q
  • Arranged in clusters
  • Most medically important specie of Staphylococcus
  • Only one that can release coagulase hence provide a positive result
A

Staphylococcus aureus

39
Q

Coagulase Test

Positive result is?

A

Clouding or solidification of plasma (clotting)

40
Q

Coagulase Test

Other species besides Staphylococcus aureus result in what?

A

Negative result

41
Q
  • Confirmatory test to specifically identify Staphylococcus aureus
  • Inoculate culture (from BAP) is subcultured using simple streak into Mannitol Salt Agar
  • Further confirms Staphylococcus aureus
A

Mannitol Fermentation Test

42
Q

Mannitol Fermentation Test

Inoculate culture (from BAP) is ____ using simple streak into ____

A

sub-cultured using simple streak into Mannitol Salt Agar (MSA)

43
Q

Components of MSA?

A
  1. Mannitol (sugar)
  2. 10% NaCl
44
Q

T or F: Most bacteria are able to grow at the salt concentration of MSA.

A

F (not grow)

45
Q

Principle of Mannitol Fermentation Test?

A

Staphylococcus aureus is capable of being a mannitol fermentor and is halo-tolerant.

This means that S. aureus can grow in high salt concentration.

46
Q

Mannitol Fermentation Test

Positive result indicators?

Note: These are results for Staphylococcus aureus only.

A
  • Fermentation results in acid formation that turns the pH indicator yellow.
  • Yellow halo or yellow growth of bacteria
47
Q

Mannitol Fermentation Test

Negative result indicators?

Note: These results are for other Staph species.

A
  • Retains its original red color from its pH indicator (phenol red)
48
Q
  • A serological test for Staphylococcus aureus since it is a very important organism (very expensive)
  • Detects DNAse or deoxyribonucleases by Staphylococcus aureus
A

DNAse Test

49
Q

What are the two methods for DNAse test?

A
  1. Dye Method
  2. HCl Precipitation
50
Q

DNAse Test provides a positive result for what two species?

A
  1. Staphylococcus aureus
  2. Serracia marcescens (gram-negative)
51
Q

Two Methods of DNAse Test

  • Toluidine Blue - (+) pink zone
  • Methyl Green - (+) clear zone

These are degraded by DNAse.

A

Dye Method

52
Q
  • Follow-up if initial results are negative (in coagulase and MSA)
  • Susceptibility
  • Similar to AST (inoculate then incubate)
A

Novobiocin Susceptibility Test

53
Q

Principle of Novobiocin Susceptbility Test?

A

Staphylococcus is resistant

54
Q

Novobiocin Susceptibility Test

Resistant results are?

Note: Only for Staphylococcus saprophyticus.

A

No ZOI or less than 14 mm

55
Q

Novobiocin Susceptibility Test

Susceptible results are?

Note: Other species except Staphylococcus saphrophyticus.

A

Zone of Inhibition is greater than 14 mm

56
Q

This species has a very visible ZOI under Novobiocin Susceptibility Test.

A

Staphylococcus epidermitis

57
Q
  • Uses tetramethyl para-phenylenediamine dihydrochloride in DMSO
  • Used when G/s is gram positive cocci is positive with catalse with varying result in coagulase, MSA, and Novobiocin (no patterns)
  • Further confirmed by other tests
A

Modified Oxidase Test

58
Q

T or F: Oxidase test is important for gram-positive bacterium.

A

F (gram-negative)

59
Q

Results for catalase, coagulase, and MSA.

Staphylococcus aureus

A

Positive for all three

60
Q

Results for catalase, coagulase, and novobiocin.

Staphyloccus saphrophyticus

A

Positive for catalase
Negative for coagulase
Resistant for novobiocin

61
Q
  • One of the most common contaminant in the laboratory and is very common in the environment
  • A pathogen if patient is very immunocompromised
  • Otherwise, it is just a contaminant
A

Micrococus luteus

62
Q

____ and ____ tests are common used to differentiate in the laboratory.

A

Modified Oxidase and Lysostaphin

63
Q

Hi, please study the summary table for these following concepts:

  1. Micrococcus vs Staphylococcus
  2. Summary for the tests discussed in this deck
A

Go na, congrats on finishing the first deck! <3

Clinical Bacteriology (33 decks)

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