Podcast Beta
Questions and Answers
Which of the following Staphylococcus species is classified as coagulase negative and is the most commonly encountered?
Which characteristic is true about the modified oxidase test?
Which of the following is NOT classified as a coagulase negative staphylococcus?
Which of the following statements about Staphylococci is correct?
Signup and view all the answers
Which of the following is true regarding coagulase negative staphylococci?
Signup and view all the answers
What must be true for the tube coagulase test to be confirmed after a negative slide test?
Signup and view all the answers
At what temperature is staphylokinase more active?
Signup and view all the answers
Why should negative tubes be held overnight at room temperature?
Signup and view all the answers
During the slide coagulase test, what must be observed within 4 hours?
Signup and view all the answers
What is the significance of using diluted plasma in the coagulase test procedure?
Signup and view all the answers
What should be done if no clot forms after the initial 4 hours?
Signup and view all the answers
What does the presence of fibrinolysin in some strains of S.aureus indicate?
Signup and view all the answers
What type of plasma is unsuitable for the coagulase test?
Signup and view all the answers
What does growth in Quadrant 1 of the Columbia Colistin-Nalidixic Acid plate indicate?
Signup and view all the answers
Which organism is indicated by absence of growth in Quadrant 2?
Signup and view all the answers
What type of hemolysis is characterized by a clear zone surrounding colonies?
Signup and view all the answers
Which of the following organisms is resistant to colistin and nalidixic acid as indicated in Quadrant 4?
Signup and view all the answers
The characteristic green, opaque zone around alpha-hemolytic colonies is indicative of which organism?
Signup and view all the answers
Which of the following statements is true about Escherichia coli in Quadrant 3?
Signup and view all the answers
What is the purpose of adding colistin and nalidixic acid to the Columbia plate?
Signup and view all the answers
Which organism would likely show a partial (alpha) hemolytic reaction on the plate?
Signup and view all the answers
What is the purpose of applying a novobiocin disk in the laboratory procedure?
Signup and view all the answers
What indicates a novobiocin-sensitive organism according to the measurement protocol?
Signup and view all the answers
Which organism is identified as novobiocin resistant based on the provided testing criteria?
Signup and view all the answers
What does a positive result for the DNase test indicate?
Signup and view all the answers
Which of the following organisms does NOT produce deoxyribonuclease?
Signup and view all the answers
What is a characteristic feature of food poisoning caused by enterotoxins A-E?
Signup and view all the answers
What is the incubation temperature required for the novobiocin susceptibility test?
Signup and view all the answers
Which statement correctly describes Bullous Impetigo?
Signup and view all the answers
What result from the Beta-lactamase test indicates a confirmed presence of the enzyme?
Signup and view all the answers
What is a key feature of Toxic Shock Syndrome associated with TSST-1?
Signup and view all the answers
Which characteristic is used to differentiate Serratia from Enterobacter?
Signup and view all the answers
How does Scalded Skin Syndrome typically present?
Signup and view all the answers
What mechanism contributes to the cytotoxic effects at higher concentrations of enterotoxins?
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.
Related Documents
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.
