Biochemical Tests for Enterobacteriaceae Identification

A biochemical test used to differentiate bacteria within the Enterobacteriaceae family based on their ability to produce indole from tryptophan.

An enzyme produced by certain bacteria that breaks down the amino acid tryptophan.

The reagent used in the indole test to detect the presence of indole, resulting in a red color at the top of the test tube.

A biochemical test used to differentiate members of the Enterobacteriaceae family based on their ability to ferment glucose and produce acidic end products.

A biochemical test used to differentiate members of the Enterobacteriaceae family based on their ability to ferment glucose and produce acetoin.

A biochemical test used to differentiate members of the Enterobacteriaceae family based on their ability to utilize citrate as a sole carbon source and ammonium as a sole nitrogen source.

A series of four biochemical tests (indole, methyl red, Voges-Proskauer, and citrate) commonly used to differentiate members of the Enterobacteriaceae family.

A family of bacteria that are commonly found in the intestines of humans and animals.

The Simon Citrate Agar (SCA) test is a microbiological test used to determine a bacteria's ability to utilize citrate as a sole carbon source. It uses Simmons Citrate Agar, a medium containing citrate as the only carbon source, sodium ammonium phosphate as the nitrogen source, and bromthymol blue as the pH indicator. The test is considered positive if the color of the agar changes from green to blue, indicating that the bacteria metabolized citrate and produced an alkaline end product. A negative result is indicated by a color change from the original green to a yellow color.

The Urea Hydrolysis Test, or Urease Test, is a microbiological test used to determine if a bacteria can hydrolyze urea into ammonia using the enzyme urease. This test utilizes Urea broth, which contains yeast extract, monopotassium phosphate, disodium phosphate, urea, and phenol red as the pH indicator. A positive result is shown by a color change from yellow to pink, indicating the production of ammonia and a rise in pH. A negative result remains yellow.

The Triple Sugar Iron Agar (TSIA) test is a multi-test agar that assesses a bacterium's ability to ferment glucose, lactose, and sucrose, while also testing for the production of hydrogen sulfide from amino acids. The agar contains these sugars, phenol red as a pH indicator, and ferrous sulfate to indicate hydrogen sulfide production. A positive result is indicated by a color change from red to yellow in the slant and/or butt of the tube. A negative result remains red.

In the Simon Citrate Agar test, a positive result is indicated by a change in color from green to blue. This change indicates that the bacteria utilized citrate as a sole carbon source, producing an alkaline end product.

In the Urea Hydrolysis Test, a positive result is indicated by a color change from yellow to pink. This indicates a rise in pH due to the production of ammonia from the hydrolysis of urea by the bacterium.

In the Triple Sugar Iron Agar (TSIA) test, a positive result in the slant of the tube indicates the bacterium can ferment lactose or sucrose and produce acid. This is indicated by a color change from red to yellow.

A positive result in the butt of the Triple Sugar Iron Agar (TSIA) test indicates that the bacterium can ferment glucose and produce acid. This is indicated by a color change from red to yellow.

In the Triple Sugar Iron Agar (TSIA) test, a black precipitate in the agar indicates the production of hydrogen sulfide by the bacterium. This is a result of the bacterium reducing sulfur compounds in the media to form hydrogen sulfide gas.

A gram-negative, lactose non-fermenting, straight or slightly curved rod with a length ranging from 1.5 to 7 µm and a width of 0.5 to 1.0 µm.

It is catalase positive, oxidase positive, and motile with one or more polar flagella.

Pseudomonas aeruginosa is the only gram-negative bacillus capable of producing the very distinctive water-soluble pigment pyocyanin.

It can be identified by a combination of tests including growth on Cetrimide Agar, growth at 42 °C, and biochemical tests such as Oxidase, Citrate, OF glucose, and Arginine Dihydrolase.

It produces colonies with a characteristic "grape-like" or "fresh-tortilla" odor on bacteriological media.

Gram-negative, rigid, curved rods or comma-shaped, highly mobile with a single polar flagellum, non-sporulated, and non-capsulated.

Catalase and oxidase tests are positive.

It ferments glucose, mannitol, maltose, mannose, and sucrose, but not inositol, arabinose, or lactose.

A gram-negative bacterium that appears in pairs (diplococci) with flattened adjacent sides resembling coffee beans under the microscope. Neisseria are non-spore-forming, non-motile, encapsulated, and non-acid-fast bacteria. They require oxygen for growth (aerobes), but can also grow in anaerobic conditions. Their growth is enhanced with 5% CO2. They grow on selective media such as Chocolate agar and Thayer-Martin agar, but not on MacConkey or Blood agar.

Laboratory diagnosis of N. gonorrhoeae usually involves obtaining samples from the vaginal, cervical, or urethral regions. Biochemical tests show that this bacteria oxidizes glucose but not maltose or sucrose. It can be cultured on Blood agar, where it appears non-hemolytic.

N. meningitides can be differentiated from other Neisseria species by its ability to produce acid from glucose and maltose, but not from sucrose or lactose. Samples for this bacteria are typically obtained from cerebrospinal fluid, particularly within neutrophils.

Neisseria can be identified through several tests including: 1. Gram staining: showing gram-negative cocci in diplococcal arrangement. 2. Kovac's oxidase test: resulting in a positive reaction. 3. Carbohydrate utilization: N. gonorrhoeae specifically ferments glucose but not maltose or lactose. 4. More advanced methods like Nuclear acid amplification tests (NAATs) can also be used for rapid and accurate detection.

For a reliable Kovac's oxidase test, ensure you use a fresh pure bacterial culture, not a nichrome wire loop as it can lead to false-positive results. Wet the commercial Taxo N disk with water and use a toothpick to transfer the colony to the wet disk. A positive reaction is indicated by a dark blue/purple color appearing within 3 minutes.

Vibrio cholerae is a gram-negative, comma-shaped bacterium that thrives in alkaline environments. As a result, it is sensitive to the acidic environment of the stomach and often survives in alkaline environments like intestinal fluids and contaminated water.

TCBS Agar (Thiosulphate Citrate Bile Salts Sucrose Agar) is a selective medium that promotes the growth of V. cholerae while inhibiting other bacteria. Colonies of V. cholerae on TCBS agar appear large and yellow due to their ability to ferment sucrose.

Vibrio cholerae can be differentiated from other species like V. parahaemolyticus by their distinct appearance on TCBS agar. V. cholerae forms large yellow colonies, while V. parahaemolyticus grows as greenish colonies.