Microbiology Isolation Techniques Quiz

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which of the following Staphylococcus species is classified as coagulase negative and is the most commonly encountered?

Staphylococcus capitis

Staphylococcus simulans

Staphylococcus epidermidis (correct)

Staphylococcus warneri

Which characteristic is true about the modified oxidase test?

Micrococcus organisms do not possess cytochrome C.

Bacteria that do not produce cytochrome C can still give a positive result. (correct)

Staphylococci react with the modified oxidase reagent to produce a dark-blue end product.

It tests the capability of bacteria to produce a dark-red end product.

Which of the following is NOT classified as a coagulase negative staphylococcus?

Staphylococcus haemolyticus

Staphylococcus aureus (correct)

Staphylococcus saprophyticus

Staphylococcus xylosus

Which of the following statements about Staphylococci is correct?

Micrococcus organisms possess cytochrome C and give a positive result in the modified oxidase test. Signup and view all the answers

Which of the following is true regarding coagulase negative staphylococci?

Staphylococcus saprophyticus is commonly associated with urinary tract infections. Signup and view all the answers

What must be true for the tube coagulase test to be confirmed after a negative slide test?

Tube coagulase tests must be performed. Signup and view all the answers

At what temperature is staphylokinase more active?

35°C Signup and view all the answers

Why should negative tubes be held overnight at room temperature?

To prevent clot lysing from fibrinolysin. Signup and view all the answers

During the slide coagulase test, what must be observed within 4 hours?

Results should be read to avoid false negatives. Signup and view all the answers

What is the significance of using diluted plasma in the coagulase test procedure?

It assists in controlling the reaction conditions. Signup and view all the answers

What should be done if no clot forms after the initial 4 hours?

Reincubate at room temperature overnight. Signup and view all the answers

What does the presence of fibrinolysin in some strains of S.aureus indicate?

It can lyse clots formed within 4 hours. Signup and view all the answers

What type of plasma is unsuitable for the coagulase test?

Plasma with citrate. Signup and view all the answers

What does growth in Quadrant 1 of the Columbia Colistin-Nalidixic Acid plate indicate?

The organism is resistant to colistin and nalidixic acid. Signup and view all the answers

Which organism is indicated by absence of growth in Quadrant 2?

Enterobacter aerogenes Signup and view all the answers

What type of hemolysis is characterized by a clear zone surrounding colonies?

Beta-hemolysis Signup and view all the answers

Which of the following organisms is resistant to colistin and nalidixic acid as indicated in Quadrant 4?

Staphylococcus aureus Signup and view all the answers

The characteristic green, opaque zone around alpha-hemolytic colonies is indicative of which organism?

Streptococcus pneumoniae Signup and view all the answers

Which of the following statements is true about Escherichia coli in Quadrant 3?

It is sensitive to both colistin and nalidixic acid. Signup and view all the answers

What is the purpose of adding colistin and nalidixic acid to the Columbia plate?

To inhibit Gram-negative organisms. Signup and view all the answers

Which organism would likely show a partial (alpha) hemolytic reaction on the plate?

Streptococcus pneumoniae Signup and view all the answers

What is the purpose of applying a novobiocin disk in the laboratory procedure?

To measure the zone of inhibition for sensitivity testing Signup and view all the answers

What indicates a novobiocin-sensitive organism according to the measurement protocol?

Zone of inhibition greater than or equal to 16 mm Signup and view all the answers

Which organism is identified as novobiocin resistant based on the provided testing criteria?

Staphylococcus saprophyticus Signup and view all the answers

What does a positive result for the DNase test indicate?

The capability of the organism to degrade DNA Signup and view all the answers

Which of the following organisms does NOT produce deoxyribonuclease?

Staphylococcus epidermidis Signup and view all the answers

What is a characteristic feature of food poisoning caused by enterotoxins A-E?

Heat stable proteins trigger vomiting through the vagus nerve. Signup and view all the answers

What is the incubation temperature required for the novobiocin susceptibility test?

35 to 37°C Signup and view all the answers

Which statement correctly describes Bullous Impetigo?

The infection is highly contagious and spreads through direct contact. Signup and view all the answers

What result from the Beta-lactamase test indicates a confirmed presence of the enzyme?

Color change to pink-red within 30 minutes Signup and view all the answers

What is a key feature of Toxic Shock Syndrome associated with TSST-1?

It involves superantigen stimulating T-cell production. Signup and view all the answers

Which characteristic is used to differentiate Serratia from Enterobacter?

Presence of deoxyribonuclease production Signup and view all the answers

How does Scalded Skin Syndrome typically present?

It leads to localized skin lesions with few blisters. Signup and view all the answers

What mechanism contributes to the cytotoxic effects at higher concentrations of enterotoxins?

Leakage by endothelial cells leading to tissue damage. Signup and view all the answers

Study Notes

Columbia Colistin-Nalidixic Acid

Selective medium used in the isolation of gram-positive cocci from clinical and non-clinical materials
Differential - blood hemolysis
Contains colistin & nalidixic acid, which inhibits gram-negative bacteria
Enterococcus faecalis - resistant to colistin and nalidixic acid, growth present in Quadrant 1
Enterobacter aerogenes - sensitive to colistin and nalidixic acid, no growth in Quadrant 2
Escherichia coli - sensitive to colistin and nalidixic acid, no growth in Quadrant 3
Staphylococcus aureus - resistant to colistin and nalidixic acid, growth present in Quadrant 4

Blood Agar Plate (BAP)

Beta Hemolysis is complete hemolysis and is characterised by a clear zone surrounding the colonies.
Staphyloccous aureus, Streptococcus pyogenes and Streptococcus agalactiae are b-hemolytic
Partial hemolysis is alpha-hemolysis and colonies will be surrounded by a green, opaque zone.
Streptococcus pneumonia is alpha-hemolytic

Modified Oxidase Test

Bacteria that produce cytochrome C produce a dark-blue end product when reacted with the modified oxidase reagent
Micrococcus organism possess cytochrome C, while Staphylococci does not.
Staphylococcus aureus will produce a negative slide coagulase test due to the clumping factors not being present in all strains.
The negative slide coagulase test must be confirmed via tube coagulase test.

Staphylococci

Genera and Species to be considered: Staphylococcus aureus
Coagulase Negative Staphylococci (Most Commonly Encountered):
- Staphylococcus epidermidis
- Staphylococcus haemolyticus
- Staphylococcus saprophyticus
- Staphylococcus schleiferi
Coagulase Negative Staphylococci (Less Commonly Encountered):
- Staphylococcus capitis
- Staphylococcus caprae
- Staphylococcus warneri
- Staphylococcus xylosus
- Staphylococcus auricularis
- Staphylococcus cohnii
- Staphylococcus simulans

Tube Coagulase Test

This test is performed to confirm a negative slide coagulase test.
The clumping factors can be masked by cell surface capsular polysaccharides.
The test must be examined periodically (1, 2 and 4 hours) for clot formation, as some strains of Staphylococcus aureus produce a fibrinolysin which lyses the clot formed within 4 hours.
Negative tubes should be held overnight at room temperature.
Procedure:
- Emulsify growth from isolated colonies in 0.5mL of diluted plasma and incubate for 1 to 4 hours at 35 to 37 degrees Celsius.
- Observe for the presence of a gel or clot
- If no clot forms after 4 hours, reincubate at room temperature overnight.
Note: Result should be read within 4 hours to prevent a false negative reaction because most strains of Staphylococcus aureus will produce a clot within this time.
Plasma with citrate is not suitable for this test as organisms such as Pseudomonas and Enterococci use the citrate and release calcium, thus forming a clot.
Expected Results:
- Positive: Medium is colorless around the test organism.
- Negative: If no degradation of DNA occurs, the medium remains green.

Novobiocin Sensitivity Test

Used to differentiate Staphylococcus aureus from other Staphylococci.
Staphylococcus aureus does not produce DNase.
Procedure:
- Allow containers to come to room temperature before use.
- Prepare a suspension of the organism equivalent to McFarland 0.5 opacity standard.
- Inoculate Mueller Hinton Agar, 5% blood agar, or tryptic soy agar plate with a sterile swab to obtain confluent growth.
- Aseptically apply one 5 µg novobiocin disk onto the inoculated agar surface and lightly press down to ensure full contact with the medium.
- Incubate plates aerobically for 18 to 24 hours at 35 to 37° Celsius.
- Measure the diameter of the zone of inhibition in millimeters, and record it as susceptible or resistant.
Interpretation:
- Resistant - zone size of <12 millimeters
- Sensitive - zone size greater or equal to 16 millimeters
- Staphylococcus saprophyticus - growth < 12 millimeters or uniform growth up to the edge of the disk
- Staphylococcus epidermidis - Zone of inhibition > 16 millimeters or larger

DNAse Test

Used to differentiate Staphylococcus aureus, which produces the enzyme deoxyribonuclease, from other Staphylococci that don't produce DNase.
Also used to distinguish Serratia (positive) from Enterobacter sp.
Moraxella catarrhalis (positive) from Neisseria

Beta (β) Lactamase Test

To detect the enzyme beta-lactamase, which confers penicillin resistance to various bacterial organisms.

Staphylococcus aureus

Resistant to hydrolysis by gastric and jejunal enzymes
Act as neurotoxins that stimulate vomiting through the vagus nerve
Group of seven heat stable proteins: A, B, C, C2, D, E and F
A-E (Food Poisoning) - heat stable and they act to stimulate neural receptors in the GI tract causing pain, vomiting, diarrhea within 6 hours of ingestion
Toxic Shock Syndrome (TSS): TSST-1 (Enterotoxin F/ Pyrogenic Exotoxin C)
- Menstruating-associated TSS = TSS associated with tampon use
- Chromosomal –mediated toxin
- Superantigen that stimulates T-cell production and production of large amounts of cytokines.
- Low concentrations = leakage by endothelial cells
- Higher concentrations = cytotoxic

Staphylococcus aureus Infections

Bullous Impetigo
- Large pustules surrounded by a small zone of erythema.
- Highly contagious infection that spreads by direct contact, fomites, or autoinoculation.
Impetigo
- Superficial cutaneous infection
- Commonly seen in newborns and young children, characterised by the formation of encrusted pustules surrounded by a red border.
Scalded Skin Syndrome
- Bullous exfoliative dermatitis that occurs primarily in newborns and previously healthy young children
- Localized skin lesions: few blisters; pemphigus neonatorum.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge on the isolation techniques using Columbia Colistin-Nalidixic Acid and Blood Agar Plate. This quiz covers the characteristics of various bacteria and their response to selective media. Challenge yourself with questions on hemolysis and antibiotic resistance.