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

Question 1

Most commonly received test request in the lab

Answer 1

Culture and Sensitivity

Question 2

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

Answer 2

To culture and perform a sensitivity assay

Question 3

• Genus and species
• What bacteria causes the infection

Answer 3

Culture

Question 4

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

Answer 4

Sensitivity

Question 5

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

Answer 5

Sensitivity

Question 6

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

Answer 6

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

Question 7

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

Answer 7

F (not including stool)

Question 8

Most common G/S result under a microscope

Sample is from an infective suppurative suture

Answer 8

Gram-positive cocci in clusters

Question 9

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.

Answer 9

Gram-positive cocci

Question 10

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

Answer 10

Results of the G/S

Question 11

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

Answer 11

Culture the organism

Inoculate on a plate or culture medium

Question 12

What are the four routinely used media culture?

Answer 12

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

Question 13

The selection of culture medium will be dependent on what?

Answer 13

G/S Result

Question 14

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

Answer 14

Blood Agar Plate (BAP)

Question 15

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

Answer 15

Chocolate Agar Plate (CAP)

Question 16

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

Answer 16

MacConkey Medium (MAC)

Question 17

• For gram-negative bacilli
• Stool is suspected of vibrio

Answer 17

TCBS Media

Question 18

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

Answer 18

MacConkey and TCBS

Question 19

This is done to get isolated growth of the colony.

inoculation method

Answer 19

Overlapping Method

Question 20

Give the optimal conditions for each category.

Temperature

Answer 20

35 to 37°C

Question 21

Give the optimal conditions for each category.

Duration

Answer 21

• BAP: 24 hours
• Selective Medium: 48 hours

Question 22

Give the optimal conditions for each category.

Environment

Answer 22

CO2 and ambient air

Question 23

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

Answer 23

24 hours

Question 24

Selective media includes?

Answer 24

1. CAP
2. MAC
3. TCBS

Question 25

Why do we collect isolated colonies?

Answer 25

To determine the genus and species

Question 26

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

Answer 26

G/S results

Question 27

* First test done on gram-positive cocci * Determines the genus * Differentiates the two most medically important gram-positive cocci genus in microbiology

Answer 27

Catalase Test

Question 28

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

Answer 28

Staphylococcus and Streptococcus

Question 29

The characteristic arrangement of Staphylococcus?

Answer 29

In clusters

Question 30

# Catalase Test (Staphylococcus) Releases ____ enzyme that reacts with ____ to produce free oxygen and water

Answer 30

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

Question 31

# Catalase Test (Staphylococcus) Releases catalase enzyme that reacts with 3% H2O2 to produce ____ and ____

Answer 31

Free oxygen and water

Question 32

# Catalase Test Positive result is?

Answer 32

Bubble formation *(effervescence)*

Question 33

# Catalase test Negative result is?

Answer 33

No bubble formation

Question 34

* There is no bubble formation in catalase test for this organism * Requires more follow-up tests

Answer 34

Streptococcus

Question 35

* This test determines the species * Serves as a follow-up for catalase based on the importance of the species identified

Answer 35

Coagulase test

Question 36

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

Answer 36

Coagulase

Question 37

# Coagulase Test Uses Rabbit's plasma either in a ____ or ____

Answer 37

Citrated or EDTA

Question 38

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

Answer 38

Staphylococcus aureus

Question 39

# Coagulase Test Positive result is?

Answer 39

Clouding or solidification of plasma *(clotting)*

Question 40

# Coagulase Test Other species besides Staphylococcus aureus result in what?

Answer 40

Negative result

Question 41

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

Answer 41

Mannitol Fermentation Test

Question 42

# Mannitol Fermentation Test Inoculate culture (from BAP) is ____ using simple streak into ____

Answer 42

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

Question 43

Components of MSA?

Answer 43

1. Mannitol (sugar) 2. 10% NaCl

Question 44

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

Answer 44

F (not grow)

Question 45

Principle of Mannitol Fermentation Test?

Answer 45

Staphylococcus aureus is capable of being a **mannitol fermentor** and is **halo-tolerant.** ## Footnote This means that S. aureus **can grow in high salt concentration.**

Question 46

# Mannitol Fermentation Test Positive result indicators? ## Footnote Note: These are results for **Staphylococcus aureus** only.

Answer 46

* Fermentation results in **acid formation** that turns the pH indicator **yellow.** * **Yellow halo** or **yellow growth of bacteria**

Question 47

# Mannitol Fermentation Test Negative result indicators? ## Footnote Note: These results are for **other Staph species.**

Answer 47

* Retains its **original red color** from its pH indicator *(phenol red)*

Question 48

* A serological test for Staphylococcus aureus since it is a very important organism *(very expensive)* * Detects DNAse or deoxyribonucleases by Staphylococcus aureus

Answer 48

DNAse Test

Question 49

What are the two methods for DNAse test?

Answer 49

1. Dye Method 2. HCl Precipitation

Question 50

DNAse Test provides a positive result for what two species?

Answer 50

1. Staphylococcus aureus 2. Serracia marcescens *(gram-negative)*

Question 51

# Two Methods of DNAse Test * Toluidine Blue - (+) pink zone * Methyl Green - (+) clear zone | These are degraded by DNAse.

Answer 51

Dye Method

Question 52

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

Answer 52

Novobiocin Susceptibility Test

Question 53

Principle of Novobiocin Susceptbility Test?

Answer 53

Staphylococcus is resistant

Question 54

# Novobiocin Susceptibility Test Resistant results are? ## Footnote Note: Only for **Staphylococcus saprophyticus.**

Answer 54

No ZOI or less than 14 mm

Question 55

# Novobiocin Susceptibility Test Susceptible results are? ## Footnote Note: Other species except Staphylococcus saphrophyticus.

Answer 55

Zone of Inhibition is greater than 14 mm

Question 56

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

Answer 56

Staphylococcus epidermitis

Question 57

* 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

Answer 57

Modified Oxidase Test

Question 58

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

Answer 58

F (gram-negative)

Question 59

# Results for catalase, coagulase, and MSA. Staphylococcus aureus

Answer 59

Positive for all three

Question 60

# Results for catalase, coagulase, and novobiocin. Staphyloccus saphrophyticus

Answer 60

Positive for catalase Negative for coagulase Resistant for novobiocin

Question 61

* 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**

Answer 61

Micrococus luteus

Question 62

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

Answer 62

Modified Oxidase and Lysostaphin

Question 63

Hi, please study the summary table for these following concepts: 1. Micrococcus vs Staphylococcus 2. Summary for the tests discussed in this deck

Answer 63

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