Table of Contents
- 1 How do you make MacConkey broth?
- 2 What ingredients are in MacConkey broth?
- 3 What is the indicator in MacConkey broth that causes it to turn yellow?
- 4 What does Salmonella look like MacConkey?
- 5 Why is violet red bile agar not autoclaved?
- 6 What is the function of lactose broth in the MPN test?
- 7 Why is MacConkey agar used?
- 8 What does it mean if a bacteria can ferment lactose?
How do you make MacConkey broth?
To prepare single strength broth add 40g to 1 litre of distilled water. Distribute into containers fitted with fermentation (Durham) tubes. Sterilise by autoclaving at 121°C for 15 minutes. MacConkey Broth has long been used as a presumptive medium for the detection of the coli-aerogenes organisms.
What ingredients are in MacConkey broth?
According to the Harmonized USP/EP/JP, MacConkey Broth is used as a selective enrichment broth, with subculture performed onto MacConkey Agar….Item No. NCM0060A.
| Formula | Liter |
|---|---|
| Pancreatic Digest of Gelatin | 20.0 g/L |
| Lactose Monohydrate | 10.0 g/L |
| Dehydrated Ox Bile | 5.0 g/L |
| Bromocresol Purple | 0.01 g/L |
Why is MacConkey broth used in MPN test?
MacConkey Broth can be used for the enumeration of coliforms by the MPN technique, selecting positive tubes that show turbidity, a colour change to red purple and gas production. The tubes that show turbidity change to red purple in colour and show gas production (bubble in the Durham tube) are considered positive.
What is the indicator in MacConkey broth that causes it to turn yellow?
Lactose-fermenting, Gram negative rods grow well in MacConkey Broth and produce acid, causing the medium to turn yellow after sufficient incubation time.
What does Salmonella look like MacConkey?
Result Interpretation on MacConkey Agar Lactose non-fermenting strains, such as Shigella and Salmonella are colourless and transparent and typically do not alter appearance of the medium. Yersinia enterocolitica may appear as small, non-lactose fermenting colonies after incubation at room temperature.
What Gram positive bacteria can grow on MacConkey agar?
Colony Morphology of some common bacteria on MacConkey Agar
| Organism | Type |
|---|---|
| Salmonella spp | Non-Lactose Fermenter |
| Pseudomonas spp | Non-Lactose Fermenter |
| Yersinia spp | Non-Lactose Fermenter |
| Gram positive bacteria |
Why is violet red bile agar not autoclaved?
DO NOT AUTOCLAVE. Mix well and pour into sterile Petri plates. Violet Red Bile Agar w/ Glucose and Lactose is a selective medium recommended for detection of Enterobacteriaceae species. This media is selective due to presence of the inhibitors; bile salts mixture and crystal violet.
What is the function of lactose broth in the MPN test?
Lactose Broth is used for the detection of coliform bacteria in water, foods and dairy products. Lactose Broth is recommended by the American Public Health Association (APHA), for the presumptive test of coliform bacteria in water, food and milk.
What is the indicator in MacConkey?
Key components of the MacConkey medium include crystal violet dye, bile salts, lactose, and neutral red (pH indicator). Crystal violet dye and bile salts halt the growth of gram-positive bacteria.
Why is MacConkey agar used?
MacConkey agar is used for the isolation of gram-negative enteric bacteria. It is used in the differentiation of lactose fermenting from lactose non-fermenting gram-negative bacteria. It is used for the isolation of coliforms and intestinal pathogens in water, dairy products and biological specimens.
What does it mean if a bacteria can ferment lactose?
Bacteria that can produce the enzyme lactase can ferment the lactose and will produce an acid waste, which will lower the pH of the media. A pH indicator, neutral red, turns bright fuchsia in color, due to the lowered pH when lactose is fermented.
Can staph grow on MacConkey?
MacConkey agar selects for organisms like Escherichia coli (Gram negative bacilli) while inhibiting the growth of organisms like Staphylococcus aureus (Gram positive cocci).