Agar TBX para microbiología Chromocult® 500 gr Merck

Agar TBX para microbiología Chromocult 500 grs Merck

SKU: ME-1161220500 Categorías: , ,

Descripción

1161220500 Agar TBX (Triptone Bile X-glucuronide) para microbiología Chromocult 500 grs Merck
Selective agar for the detection and enumeration of Escherichia coli in foodstuffs, animal feed and water. The medium complies with the recommendations of ISO 16649 -1+2, 2000.

Mode of action
The presence of the enzyme – D – glucuronidase differentiates most E.coli ssp. from other coliforms. E.coli absorbs the chromogenic substrate 5 – bromo – 4 – chloro -3- indolyl – – D -glucuronide ( X- – D – glucuronide ). The enzyme -glucuronidase splits the bond between the chromophore 5 – bromo -4 -chloro -3-indolyle – and the – D – glucuronide. E.coli colonies are coloured blue-green.
Growth of accompanying Gram-positive flora is largely inhibited by the use of bile salts and the high incubation temperature of 44°C.

Typical composition ( g / Litre )
Peptone 20.0;
bile salts No. 3 1.5;
X- – D – glucuronide 0.075;
agar-agar 10.0.

Preparation
Suspend 31.6 g in 1 litre of demin. water by heating in a boiling water bath or in flowing steam until the medium is completely dissolved. Autoclave at 121°C for 15 min.
Cool to 45 – 50°C in a water bath, mix gently and pour 15 ml in sterile Petridishes. pH: 7.2 +/- 0.2 at 25°C. The prepared medium is clear and yellowish. If stored at +2 to +8°C and protected from light plates or medium in bottles are stable for 4 weeks.

Selective agar for the detection and enumeration of Escherichia coli in foodstuffs, animal feed and water. The medium complies with the recommendations of ISO 16649 -1+2, 2000.

Experimental procedure
The pour plate or membrane filtration technique can be used to inoculate the medium.
Pour plate technique: Pipette 1 ml of a homogenate or appropriate 10 -fold dilution into a sterile Petridish, add 15 ml of the medium
(cooled to 45 – 50°C ) and mix gently.
Fresh or raw samples: Plates are incubated at 44°C for 18 -24 h aerobically.
Membrane filtration technique: Filter an aliquot of a liquid sample through a Cellulose – mix- ester Membrane e. g. Gelman GN 6.
Fresh or raw samples: Transfer the membrane-filter to ChromoCult TBX agar and incubate at 44°C for 18 -24 h.
ISO 16649-1 membrane filtration technique: For the recovery of sublethally injured E.coli.
Resuscitation step: The membrane filter is transferred to Mineral modified Glutamat Agar (MMGA) and incubate at 37°C or 30°C
for 4 h. After this resuscitation step transfer the membrane-filter to ChromoCult TBX Agar and incubate at 44°C for another 18 -20 h.
ISO 16649-2 pour plate technique: Pipette 1 ml of a homogenate or oppropriate 10-fold dilution into a sterile Petridish, add 15 ml
of the medium (cooled to 45-50°C) and mix gently.
Resuscitation step: For the recovery of sublethally injured E.coli, plates are incubated at 37°C or 30°C for 4 h. After this resuscitation
step incubation is continued at 44°C for another 18-20 h.

Results
E.coli colonies are blue – green ( X- – D- glucuronide reaction ).
Attention: – Glucuronidase-negative E.coli strains (3 – 4 %) form colourless colonies, e. g. E.coli 0157, or they cannot grow
at elevated temperature of 44°C, e.g. E. coli 0157: H7

Información adicional

Peso 1 kg