Part of Thermo Fisher Scientific
Organisms in the Clinical sector this product works with:
Featured Organism: Staphylococcus sp
CHROMOGENIC UTI MEDIUM (CLEAR)
Code: CM1050
A chromogenic medium for the presumptive identification and differentiation
of all the main micro-organisms that cause urinary tract infections (UTIs).
Formula |
gm/litre |
Peptone |
15.0 |
Chromogenic mix |
13.0 |
Agar |
15.0 |
Final pH 7.0 ± 0.2 |
|
Directions
Suspend 43 grams of Chromogenic UTI Medium in 1 litre of distilled
water. Mix well and sterilize by autoclaving at 121°C for 15 minutes. Cool
the medium to 50°C and pour into sterile Petri dishes.
Description
Chromogenic UTI Medium (Clear) is a differential agar which provides presumptive
identification of the main pathogens which cause infection of the urinary tract.
This medium uses the same chromogenic substrates as the existing opaque Chromogenc
UTI Medium CM0949 but has a clear background to make multiple sample testing
easier.
Chromogenic UTI Medium (Clear) contains two specific chromogenic substrates
which are cleaved by enzymes produced by Enterococcus spp., Escherichia
coli and coliforms.
In addition, it contains tryptophan which indicates tryptophan deaminase
activity (TDA), indicating the presence of Proteus spp. It is based
on Cystine Lactose Electrolyte Deficient (CLED) Medium which provides a valuable
non-inhibitory
diagnostic agar for plate culture of other urinary organisms, whilst preventing
the swarming of Proteus spp.
The chromogen, X-glucoside, is targeted
towards ß-glucosidase enzyme
activity, and allows the specific detection of enterococci through the formation
of blue
colonies.
The other chromogen, Red-Galactoside, is cleaved by the enzyme ß-galactosidase
which is produced by Escherichia coli, resulting in pink colonies. Any uncertainty
in identification may be resolved by removing suspect colonies from the plate
and performing an indole test using Microbact Reagent spot indole DMACA (oxoid
order code MB1448).
Cleavage of both the chromogens by members of the coliform
group, results in purple colonies.
The medium also contains tryptophan which acts
as an indicator of tryptophan deaminase activity (TDA), resulting in halos around
the colonies of Proteus,
Morganella and Providencia spp.
Organism | ß-galactosidase |
ß-glucosidase |
TDA |
Colony colour |
Enterococci | - |
+ |
- |
Blue |
Escherichia coli | + |
- |
- |
Pink |
Coliforms | + |
+ |
- |
Purple |
Proteus/Morganella |
- |
- |
+ |
Brown |
Pseudomonads | - |
- |
- |
Fluoresce |
Staphylococci | - |
- |
- |
Normal pigmentation |
It should be noted that organisms with atyptical enzyme patterns may give
anomalous reactions. For example, in a trial, over 45% of Enterobacter
cloacae were shown to lack ß-glucosidase, resulting in pink colonies
which were indistinguishable from Escherichia coli1. In
such cases an indole test can be performed using DMACA indole (do not use Kovac’s
as the
colour of
the Escherichia
coli colonies may interfere with the red colour of a positive indole test).
The test should be performed on filter paper, not directly on the plate. This
test will distinguish between Escherichia
coli and Enterobacter spp, and also between Proteus mirabilis and
other species.
Appearance:
Dehydrated Chromogenic UTI Medium (Clear) is a free-flowing straw -colored
powder.
The prepared medium is a straw-colored, transparent agar.
Precautions:
Chromogenic UTI Medium (Clear) should only be used for in vitro diagnostic
purposes. Do not use beyond the stated expiry date, or if the product shows
any sign of deterioration.
Storage conditions and Shelf life
The dehydrated medium should be stored
at 10-30°C and used before the expiry date on the label.
Prepared
medium may be stored, out of direct light for
up to 2 weeks at 2-8°C.
Quality control
Positive controls: |
Expected results |
Escherichia coli ATCC® 25922 * | Good growth; pink coloured colonies. |
Enterobacter aerogenes ATCC® 13048 * | Good growth; purple coloured colonies. |
Enterococcus faecalis ATCC® 29212 * | Good growth; blue-green coloured colonies. |
Proteus hauseri ATCC® 13315 * | Good growth; straw coloured colonies; brown halo. |
Staphylococcus aureus ATCC® 25923 * | Good growth; white colonies. |
Negative control: |
|
Uninoculated medium. |
No change |
* This organism is available as a Culti-Loop®
Reference
Data on file at Oxoid.