Lab Questions

Different types of media used in lab

General Purpose Medium or General Medium

General Purpose Medium or General Medium

Nutrient Agar

Enrichment Medium

Blood Agar

Enrichment Medium

Chocolate Agar

Differential Medium

Mac Conkey Agar

Differential Medium

TSI (Triple Iron Sugar Iron Agar)

Differential Medium

Hugh and Liefson Medium for Oxidation/Fermentation (O/F TEST)

DNA Agar plate

Used to see if the organism has the ability to produce the exoenzyme deoxyribosenuclease. To cleave DNA

Mannitol salt agar

selective and differential medium in the isolation of staphylococci. It contains 7.5% sodium chloride and selects for those bacteria which can tolerate high salt concentrations. MSA also distinguishes bacteria based on the ability to ferment the sugar mannitol

Mac Conkey Agar

Used to differentiate gram negative bacteria that can ferment lactose

Gamma Reaction

The blood cells are not lysed and there isnt a change in agar colour.

Alpha Reaction

The blood cells are partially lysed and have a green hue to the colonies. This indicates that iron is left behind.

Beta Reaction

Complete absorbance of the blood cellls and a halo is seen around the colonies. This means the bactiera is capable of heamolysis.

TSI (Triple Sugar Iron Agar)

Used to differentiate enteric bacteria depending on the ability to ferment lactose, sucrose and glucose.

Hugh and Leifson Medium (O/F)

Test to see whether glucose is metabolized by oxidation and fermentation.

O/F Colour for oxidation Closed tube

Green

O/F Colour for oxidation open tube

Yellow

O/F Colour for fermenting sealed and open tube

Yellow

No action of glucose for O/F

Green

Braid Parker OF medium

A moderately selective and differential medium for the isolation and enumeration of Staphylococcus aureus in foods, environmental, and clinical specimens

A positive reaction will show dark colonies with a clear halo around the colonies

Trehalose broth

sugar that some bacteria can use because of an enzyme that begins the breakdown of this compound.

Phenol red is used to determine whether the microbe can use the sugar trehalose for carbon and energy.

A positive reaction would indicate the colour change to yellow

Ornthine decarboxylase medium

To see if the microbe can use the amino acid ornithine as a source of carbon and energy for growth.

Use of ornithine is accomplished by the enzyme ornithine decarboxylase.

If colour goes to yellow the glucose can be made but if goes to purple then this means the enzyme can be used.

Bile Aesculin medium

Selective and differential

Bile salts prevent the growth of gram positive bacteria that is not Strep group D and enterococci .

A positive reaction will indicate dark brown deposists on the agar plate.

6.5% salt Broth

Indication if the microbe can grow in high salt environments.

Streptococcal grouping kit

A latex agglutination kit that indentifies the strep bacteria by the antigens on the bacteria, in the presence of the antigens the latex molecules will agglutinate indicating the identification of Strep molecules.

CAMP test

This is done on Blood agar medium and is used to identify the different beta heamolytic Strep species.

This is done by streaking a line of Staph and then streaking the Strep species perpendicular to the Staph streak.

A positive reaction will show a arrowhead zone indicating enhanced heamolysis by the Strep species.

Optochin Susceptibility test

This is an antibiotic susceptibility test used to see if the bacteria has a susceptibility to Optochin

A positive reaction will indicate a zone of inhibition around the Optochin disk.

This is done on blood agar plates.

XLD Agar

isolate the species of shigella and salmonella

Selective and differential medium

Selective as it inhibts for gram positive bacteria and allows the growth of gram neg

Fermentation of the sugars xylose and lactose will show YELLOW colonies

hs2 PRODUCTION shows black colonies

EMB Media

Selective and differential medium

Selective as it inhibts for gram positive bacteria and allows the growth of gram NEG

Lactose ferment - green metallic sheen

Non-Lactose ferment - Colourless colonies

Hektoen Enteric Agar

Selective and differential medium

Selective as it inhibts for gram positive bacteria and allows the growth of gram NEG

Fermentation (lactose, sucrose and salicin) indication of acid production so Yellow colonies

Peptone (carbon source) = Alkaline = Blue/green colonies

Hydrogen sulfide production (sodium thiosulphate and iron citrate) = Black colonies

Urea Broth

If M.O hydrolysing urea to produce ammonia & carbon dioxide = Alkaline = Pink

ONPG Broth

ONPG test is used to detect the enzyme βgalactosidase production.

late lactose fermenters & non-lactose fermenters = colorless colonies on MacConkey agar.

Positive result will change colour to yellow

Fermentation of lactose depends on two enzymes:

• Permease • Beta-galactosidase

Permease allows lactose to enter the bacterial cell wall, where it is then broken down into glucose and galactose by betagalactosidase

Indole media

To detect the ability of organism to produce enzyme tryptophanase.

Differential media

If M.O produce tryptophanase: Tryptophan hydrolysis to = Ammonia + Indole + Pyruvic acid

----- add Kovacs reagent -----

Red ring (positive result)

Citrate media

M.O utilize citrate as the sole carbon source

Differential media

Sodium citrate ------ Sodium bicarbonate + Ammonia (NH3) ------ alkaline (blue)

Blue will indicate a positive result of the microorganism using citrate.

Glucose Peptone Water Media

Differential

Done for the indication of the fementation of carbohydrate and also gas production.

If ferments Glucose, colour will turn Yellow

Motility Media

Determine the motility of microorganisms (flagella)

PDA media

Phenylalanine Deaminase Media

To determine if M.O deaminate phenylalanine to phenyl pyruvic acid.

Phenylalanine ------phenyl pyruvic acid ---

Add 10% ferric chloride ----Green(positive)

MR/VP Media Voges–Proskauer

To determine if an organism produces acetylmethylcarbinol from glucose fermentation.

M.O digest glucose to acetylmethylcarbinol-----

First, add the ∝- naphthol; then, add 40% KOH ----

If Red/Purple then it’s positive

Cetrimide agar plates

Selective and Differential Media

Positive indication of colony growth will be fluroscent green colonies , negative will show no growth.

Cetrimide is a quarternary ammonium compound with bactericidal activity against a broad range of Gram-positive organisms and some Gram-negative organisms.

Arginine dihydrolase medium

To distinguish from other groups of Pseudomonas spp.

The purpose is to see if the microbe can use the amino acid arginine as a source of carbon and energy for growth.

Colour change from purple to yellow and then back to purple is positive reaction

Nitrate medium

Recommended for detecting nitrate-reducing and indole-producing microorganisms