38 Questions
What is the purpose of the citrate test?
To distinguish bacteria capable of growth in a citrate medium
What happens to the pH of the medium when bacteria grow in it?
It becomes alkaline
What is the function of the bromthymol blue indicator?
To determine the pH of the medium
What is the purpose of the DNA hydrolysis test?
To determine the ability of an organism to hydrolyze DNA
What is the color of the DNA-methyl green complex?
Green
What happens to the color of the medium if an organism can hydrolyze DNA?
It becomes colorless
What is the primary purpose of the test described?
To determine the ability of an organism to produce and maintain stable acid end products
What is the role of the MR indicator in the test?
To detect mixed acid fermentation
What is the color of the MR indicator at pH 4.4?
Red
What does a clear red result indicate?
A positive result
What does the VP test detect?
The ability of an organism to convert acid products to acetoin and 2,3-butanediol
What is the purpose of the VP test?
To determine the ability of an organism to convert acid products to acetoin and 2,3-butanediol
What type of fermentation is detected by the MR indicator?
Mixed acid fermentation
What is the result of a yellow MR indicator?
Negative result
What is a characteristic of E. coli O157:H7?
It doesn't ferment sorbitol
What is the primary reservoir of Edwardsiella tarda?
Reptiles and fresh water fish
What is a common source of Salmonella transmission?
Poultry
What is a characteristic of Shigella?
It is motile
What is a common location for Shigella infection?
Day-care centers
What is a characteristic of Citrobacter freundii?
It is motile
What is a characteristic of Salmonella typhi?
It has a Vi antigen
What is a way to differentiate Edwardsiella tarda from Salmonella?
Indole test
What is the characteristic of Salmonella in the citrate test?
Colorless
Which of the following bacteria is a Rapid Lactose Fermenter?
Klebsiella
What is the characteristic of Enterobacter in the citrate test?
Produces pink color
Which of the following bacteria is a Late Lactose Fermenter?
Hafnia
What is the characteristic of Serratia in the citrate test?
Produces colorless medium at first, turning pink
Which of the following bacteria is a Non-Lactose Fermenter?
Salmonella
What is the characteristic of Proteus in the citrate test?
Produces colorless medium
Which of the following bacteria is aerogenic?
Escherichia
What is the primary function of the test that determines an organism's ability to hydrolyze tryptophan?
To hydrolyze tryptophan to pyruvate, ammonia, and indole
What is the reaction between Kovac's reagent and indole?
Produces a red color
What is the expected result of a positive test?
A pink to wine-colored ring forms
What is the purpose of the Lysine Iron Agar (LIA) test?
To differentiate gram-negative bacilli
What is the role of ferric ammonium citrate in Lysine Iron Agar?
It is the source of iron
What happens to the butt of the Lysine Iron Agar medium when glucose is fermented?
It becomes acidic (yellow)
What is the function of sodium thiosulfate in Lysine Iron Agar?
It detects the presence of hydrogen sulfide
What is the composition of the medium in Lysine Iron Agar?
Lysine, peptones, glucose, ferric ammonium citrate, and sodium thiosulfate
Study Notes
Microbiology Laboratory Tests
- Pyruvate can enter the organism's metabolic cycle for energy production
- Bacteria capable of growth in citrate medium convert ammonium phosphate to ammonia and ammonium hydroxide, creating an alkaline pH
- Bromthymol blue indicator turns from green to blue in the presence of alkaline pH
DNA Hydrolysis (Dnase Test Agar)
- Purpose: differentiate organisms based on deoxyribonuclease production
- Principle: determines an organism's ability to hydrolyze DNA
- Expected result: pink to wine-colored ring after adding Kovac's reagent
Tryptophanase Test
- Purpose: determines an organism's ability to hydrolyze tryptophan to form indole
- Principle: tryptophanase-producing bacteria hydrolyze tryptophan to pyruvate, ammonia, and indole
- Expected result: pink to wine-colored ring after adding Kovac's reagent
Lysine Iron Agar (LIA)
- Purpose: differentiates gram-negative bacilli based on decarboxylation or deamination of lysine and H2S formation
- Principle: lysine iron agar contains lysine, peptones, glucose, ferric ammonium citrate, and sodium thiosulfate
- Expected result: acid production (yellow) in the butt of the medium
Methyl Red (MR) and Voges-Proskauer (VP) Tests
- Purpose: determines the ability to produce and maintain stable acid end products from glucose fermentation
- Principle: methyl red detects mixed acid fermentation, and VP detects the ability to convert acid products to acetoin and 2,3-butanediol
- Expected result: clear red (positive), yellow (negative), or shades of orange (inconclusive)
Bacterial Identification
- Shigella: causes dysentery, found in crowded or substandard conditions
- Edwardsiella tarda: opportunistic, found in reptiles and fresh water fish
- Salmonella: causes typhoid fever, bacteremia, and enterocolitis, found in poultry
- Citrobacter freundii: causes nosocomial infections
- Klebsiella: causes pneumonia, found in humans and the environment
- Enterobacter: causes opportunistic infections
- Serratia: causes opportunistic infections
- Proteus: causes urinary tract infections
- Morganella: causes opportunistic infections
- Providencia: causes opportunistic infections
- Yersinia: causes plague and gastrointestinal infections
A quiz on microbiology tests, including citrate test and DNA hydrolysis, to identify bacterial growth and hydrolysis of DNA.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
