Lancefield Grouping & Hemolysis Testing Quiz

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Questions and Answers

What is the purpose of the methyl red test in microbiology?

To detect bacteria producing stable acidic end products from glucose (correct)

To identify bacteria that can utilize citrate as a carbon source

To differentiate between bacteria based on their ability to hydrolyze tryptophan

To identify bacteria based on their fermentation of lactose

Which differential medium is used in the Voges-Proskauer test?

Simmon’s citrate agar

MAcConkey agar

Tryptone broth

MR-VP broth (correct)

What pH indicator is used in the citrate hydrolysis test, and what does it change to indicate a positive result?

Bromthymol blue, turns blue (correct)

Methyl red, turns yellow

Phenol red, turns pink

Litmus, turns purple

Which product is detected in the indole test after adding Kovac’s reagent?

Indole Signup and view all the answers

Which of the following fermentation pathways does the methyl red test assess?

Mixed acid fermentation pathway Signup and view all the answers

In the citrate hydrolysis test, what do the alkaline products produced signify?

The bacteria successfully utilized citrate as a carbon source Signup and view all the answers

What may cause a false negative result in carbohydrate fermentation tests?

Testing a sample that has been stored for over 24 hours Signup and view all the answers

What is the primary substrate for the Voges-Proskauer test?

Glucose Signup and view all the answers

What is the differential medium that distinguishes Proteus species based on urease production?

Urea broth Signup and view all the answers

What is a common detectable product in the methyl red test?

Acetic acid Signup and view all the answers

Which substrate is tested in urea broth to determine urease activity?

Urea Signup and view all the answers

What color indicates a positive result for urease activity in urea broth?

Bright pink Signup and view all the answers

What is the role of ammonia produced during the urea hydrolysis process?

To increase the pH, making it more alkaline Signup and view all the answers

Which of the following mistakes could lead to a false result in a urease test?

Contamination of the test sample Signup and view all the answers

What is the primary role of lactose in MacConkey agar?

To differentiate bacteria based on their ability to ferment lactose Signup and view all the answers

What color indicates lactose fermentation in MacConkey agar?

Pink/red colonies Signup and view all the answers

Which test series is used to differentiate members of the Family Enterobacteriaceae?

IMViC series of tests Signup and view all the answers

Which of the following describes a potential mistake that could lead to false results on MacConkey agar?

Incubating the agar for over 24 hours Signup and view all the answers

What is the pH indicator used in urea broth to demonstrate urease activity?

Phenol red Signup and view all the answers

What is the purpose of triple sugar iron agar?

To differentiate members of the Enterobacteriaceae family Signup and view all the answers

Which sugar in triple sugar iron agar is used to detect hydrogen sulfide production?

Glucose Signup and view all the answers

How does the pH indicator neutral red function in MacConkey agar?

It changes color to indicate lactose fermentation Signup and view all the answers

What are non-coliforms in the context of MacConkey agar?

Bacteria that do not ferment lactose and produce colorless colonies Signup and view all the answers

What indicates a lactose fermentation reaction in triple sugar iron agar?

Color change of medium to yellow Signup and view all the answers

Study Notes

Lancefield Grouping and Hemolysis Testing

Differentiates streptococci and enterococci into groups A-T
Based on carbohydrate composition of antigens on cell wall surfaces
Group A: Streptococcus pyogenes
Group B: Streptococcus agalactiae
Group D: various streptococci and enterococci

Bacitracin and Optochin Sensitivity Testing

Bacitracin test: differentiates Group A (Streptococcus pyogenes) from Group B (Streptococcus agalactiae)
- Grow bacteria on blood agar
- Place bacitracin disc on agar
- Check for clear zone (zone of inhibition)
- 10mm zone = sensitive; no zone = resistant
Optochin test: distinguishes Streptococcus pneumoniae(sensitive) from other alpha-hemolytic streptococci like Streptococcus viridans(resistant)
- Grow bacteria on blood agar
- Place optochin disc on agar
- Look for zone of inhibition
- Zone = sensitive; no zone = resistant

Bile Esculin Agar

Selective and differential medium
Separates Group D streptococci and enterococci from other streptococci
Selective ingredient: bile (inhibits most non-group D organisms)
Differential ingredient: esculin (a sugar compound that certain Group D streptococci can chemically alter)
Color indicator: dark brown/black iron precipitate forms when esculin is broken down

6.5% Salt Broth

Selective medium
High sodium chloride concentration
Selects for enterococci (like Enterococcus faecalis) and against other bacteria.

MacConkey Agar

Selective and differential medium for Enterobacteriaceae
Selective ingredient: bile salts (inhibits gram-positive bacteria)
Differential ingredient: lactose (color indicator shows if lactose is fermented)
- Pink/red colonies = acidic pH (fermented lactose)
- Colorless colonies = neutral pH (did not ferment lactose)

Triple Sugar Iron Agar (TSIA)

Differential medium for Enterobacteriaceae
Differentiates based on fermentation of sugars (glucose, lactose, sucrose) and production of hydrogen sulfide (H2S)
- Yellow slant + yellow butt = glucose fermentation
- Red slant + yellow butt = glucose fermentation only
- Red slant + red butt = no fermentation
- Black precipitate in butt = H2S production

Urea Broth

Differential medium, distinguishes Proteus from other lactose non-fermenters
Detects urease (enzyme that degrades urea)
Positive result = pink color indicates ammonia production and alkaline pH.

Indole Test (Tryptone Broth)

Differentiates bacteria based on their ability to produce tryptophanase (breaks down tryptophan).
Positive = red ring after adding Kovac's reagent.

Methyl Red Test (MR-VP Broth)

Detects mixed acid fermentation products (acidic pH).
Positive = red color.

Voges-Proskauer Test (MR-VP Broth)

Detects 2,3-butanediol fermentation products
Positive result = red color

Citrate Test (Simmon's Citrate Agar)

Differentiates bacteria based on their ability to use citrate as a sole carbon source.
Positive result = blue color due to alkalinity.

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Description

Test your knowledge on Lancefield grouping and hemolysis testing in streptococci and enterococci. This quiz covers key concepts such as bacitracin and optochin sensitivity testing, along with the use of bile esculin agar. Perfect for microbiology students and enthusiasts!