Danh mục
Formula
Tryptone: 20.0
Lactose :5.0
Bile Salts No. 3 :1.5
Di-potassium phosphate :4.0
Mono-potassium phosphate :1.5
Sodium chloride :5.0
Directions
Dissolve 37 g in 1 litre of distilled water. Dispense into final containers and sterilize by autoclaving at 121oC for 15 minutes.
Principles and uses
Chromogenic Coliforms Agar (CCA) is a selective medium for the detection of E. coli and other coliforms in waters and foods. The recovery and enumeration of Escherichia coli and coliforms are important indicators of environmental and food hygiene. CCA is especially recomended for waters with low bacterial numbers, whether it is drinking water, disinfected pool water, or finished water from drinking water treatment plants.
The interaction of ingredients in the medium, such as peptone, sorbitol and pyruvate, grants a quick colony growth, including infectious coliforms and also permits the recovery of sublethal thermally injured coliforms. Tergitol-7 inhibits Gram-positive bacteria and some Gram-negative without affecting the coliform bacteria. Sodium chloride maintains the osmotic balance and phosphate salts act as a buffer system. Bacteriological agar is the solidifying agent.
Detection of ß-glucuronidase is widely used to differentiate Escherichia coli, as the enzyme is present in E. coli but not in other member of coliform group. The chromogenic mixture contains chromogenic substrates: Salmon-GAL and X-glucuronide. Coliform enzymes produced, ß-D-galactosidase and ß-D-glucuronidase, cleave these substrates resulting in the different coloration of bacteria colonies. The ß-D-galactosidase cleaves Salmon-GAL substrate, and gives a salmon-red color to the coliform colonies. The ß-D-glucuronidase, enzyme characteristic of E. coli, cleaves X-glucuronide, giving a blue color to these colonies. E. coli has the two enzymes and cleaves both chromogenic substances giving dark blue to violet colonies. Total coliforms are the sum of E. coli colonies plus salmon-red colonies. The addition of tryptophan to the medium allows the performance of the Indole test for further E.coli confirmation.
For the enumeration of E. coli and coliform bacteria according to ISO 9308:
- Filter sample through a membrane .
- Place the membrane filter over a E. Coli Coliforms Chromogenic Agar plate.
- Invert Petri dish and incubate at 36±2 ºC during 21±3 h.
- Count the ß-D-galactosidase colonies (pink to red in color) as presumptive coliform bacterias that are not E. coli
-To avoid false positive results, caused by oxidase-positive bacteria, for example, Aeromonas spp, confirm bacterial colonies through an oxidase-negative reaction. - The positive colonies ß-D-galactosidase and ß-D-glucuronidase (dark blue to violet) are counted as E. coli.
- The total coliform bacteria count is the sum of oxidase-negative colonies, ß-D-galactosidase-positive colonies (pink to red) and all colonies which dark blue to violet.
- Some Shigella strains contain the enzyme ß-D-glucuronidase and can grow as light blue colonies.
Violet Red Bile Agar (VRBL) is a selective medium used for the detection and enumeration of coliform and thermotolerant coliforms food products.
Chromogenic coliform agar (CCA) conforms to the ISO 9308-1 guidelines for the detection, enumeration and isolation of coliforms and more specifically Escherichia coli in water samples by the membrane-filtration technique.
The colonial differentiation is provided by the chromogenic substrates, Salmon-GAL and X-glucuronide.
Salmon-GAL is used for the detection of ß-D-galactosidase enzymatic activity.
X-glucuronide is used for the detection of ß-D-glucoronidase enzymatic activity.
β-D-galactosidase, expressed by all coliforms, cleaves the Salmon-GAL substrate and producing red/pink coloured colonies.
Unlike other coliforms, Escherichia coli cleaves both Salmon-GAL and X-glucuronide producing a violet/blue coloured colonies.
Tryptophan is used to increase detection reliability by improving the indole reaction.
The peptones, sodium pyruvate and sorbitol support bacterial growth and simple recovery of sub-lethal thermally injured coliforms.
Sodium di-hydrogen phosphate and di-sodium hydrogen phosphate phosphate buffer the medium and sodium chloride is used to achieve osmotic balance.
The selectivity is attained by the addition of Tergitol® 7 as it inhibits the growth of Gram-positive bacteria.
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Bromocresol Purple (BCP) Lactose Agar is a non-selective medium, used for the differentiation of Enterobacteriaceae. It is used for the confirmation of coliforms in the context of the standard T90-425, for the bacteriological examination of containers and recipients used in water bottling.
Tergitol 7 Agar is used for the enumeration of Escherichia coli and coliform bacteria in water, notably potable water, through the membrane filtration method.
This media is also used for testing swimming pool water.
Lactose Broth is used principally as a liquid enrichment media for the detection of Escherichia coli in cosmetic products, if neutralizers or dispersal agents are not necessary. It is also adapted to the culture of all Gram negative bacteria. Armed with a Durham tube, it can detect the fermentation of lactose.
Principles and uses
Endo Agar Base is a differential and moderately selective culture medium for the detection and confirmation of coliforms and other enteric microorganisms in waters, milk, dairy and other food products.
It uses fuchsin to differentiate between positive lactose-fermenting and lactose non-fermenting bacteria. Acetaldehyde production by lactose-fermenting organisms such as E. coli produce characteristic red colonies and a red surrounding area, marked by its reaction with Sodium sulphite in the presence of fuchsin. Lactose non-fermenters form colorless, transparent colonies.
Peptone provides nitrogen, vitamins, minerals and amino acids essential for growth. Lactose is the fermentable carbohydrate providing carbon and energy. Dipotassium phosphate acts as a buffer system. Bacteriological agar is the solidifying agent.
Formula:
For 1 liter of media :
- Pancreatic digest of meat.......................................................................................... 10,0 g
- Lactose...................................................................................................................... 10,0 g
- Dipotassium phosphate............................................................................................... 3,5 g
- Sodium sulfite.............................................................................................................. 2,5 g
- Basic fuchsin .............................................................................................................. 0,5 g
- Bacteriological agar................................................................................................... 15,0 g
pH of the ready-to-use media at 25 °C : 7,5 ± 0,2.
Preparation
Dissolve 41,5 g of dehydrated media (BK057) in 1 liter of distilled or demineralized water.
Slowly bring to boiling, stirring with constant agitation until complete dissolution.
Dispense in tubes or flasks.
Sterilize in an autoclave at 121 °C for 15 minutes.
Cool and maintain in a molten state at 44-47 °C.
Mix well in order to distribute any precipitate.
Pour into sterile Petri plates and let solidify on a cool, even surface.
Dry the plates in an incubator, covers partially removed.
Desoxycholate (0.1%) Lactose Agar is a selective medium for the enumeration of coliform bacteria in milk, dairy products and other food products. The medium is also recommended for the isolation and culture of Shigella.
Bromocresol Purple (BCP) Lactose broth is used as enrichment media for the enumeration of coliforms and of thermotolerant coliforms in water