By: Kassapa Ellepola
‘Traditional
standard growth media’ for microorganisms, since its introduction in the 1800’s
has dominated for more than two centuries as the most widely used growth media
for bacteria and fungi. The discovery of Agar, extracted from Red Algae became
the best solidifying agent for microbiological media and not much has changed
in these media apart from their chemical composition depending on the purpose (general
purpose, enrichment, selective etc) of the medium.
Dr. Alain
Rambach in 1979 pioneered the invention of ‘chromogenic culture media’ that at
the time was believed would make a promising change in the medical field as
well as in industry. Chromogenic Agar is a medium that assists the isolation
and identification of certain pathogenic microorganisms with the aid of colony
color, colony morphology and colony growth. Pathogenic microorganisms are fastidious. Therefore he
equipped the medium with special nutrients that enhance their growth while inhibiting
the growth of less fastidious organisms.
The normal
procedure to grow fastidious organisms will be to carryout enrichment before growing
in standard culture media. The proven technique is to carry out Enrichment in
broths before plating out. This has been practiced for a long time. But with
the use of chromogenic agar, will this be necessary!
Detection systems of conventional culture media combine various
carbohydrates, amino acids, and glycosides with a suitable indicator-system.
The incorporation of enzyme substrates as a detection system has led to
the development of numerous primary isolation media.
Chromogenic enzyme substrates
consist of chromophors linked to an enzyme-recognizing-part, such as a
carbohydrate, amino acid or phosphate. Specific enzymes produced by the target
microorganism cleave the chromogenic substrate liberating the chromophor,
which highlight the micro-organism by coloration of the grown colony.
There is a diversity of chromogenic agar that is available for
microbiological work. One such medium is the chromogenic Agar for identifying ‘methycillin
resistant Staphylococcus aeureus’ (MRSA).
There are chromogenic media designed for identifying Neisseria sp as well.
Infections due to Salmonella have become a principle health issue
related with the food industry as well as with water quality. Rapid
identification methods are needed for prevention of outbreaks. ‘Salmonella Chromogenic media’ has been designed
based on Salmonella’s ability to
utilize one of two chromogenic substances in the medium while others in family
Enterobacteriaceae can utilize both.
‘Salmonella
Chromogenic Agar Base’ combines two ‘chromogens’ for the detection of Salmonella sp.
‘Magenta-caprylate’ and ‘X-gal’. β-D-galactosidase acts on X-gal as it is a
substrate for the enzyme . Lactase
negative Salmonella species hydrolyse the chromogen,
Mag-caprylate giving magenta colored colonies. The medium contains bile salts
to inhibit the growth of Gram-positive organisms. The medium may also contain novobiocin
to inhibit Proteus growth and cefsulodin to inhibit
growth of Pseudomonads.
Not only for bacteria, but it also works for fungi such as Candida sp which its different strains
are colored differently in a chromogenic agar plate.
Hospitals and nursing care institutes find it very important to find immediate
identification of pathogens. Specialized chromogenic agar can be used for this
purpose as it would easily inhibit undesirable organisms while enhancing the
growth of the fastidious pathogens while giving colored colonies for pathogens.
Use of chromogenic agar will aid the food industry as well.
Using
chromogenic Agar is distinctively advantageous than traditional methods. Within
24 hours after inoculation, the chromogenic agar medium allows the presumptive
identification of the pathogen with the aid of colony colors. But colonies
grown on a traditional agar plate does not allow direct identification.
Therefore other methods such biochemical tests should be employed which may
involve costly tool kits and would take another day or two to give the results.
Improved accuracy
compared to traditional agars, faster detection of targeted organisms, cost
effective methodologies, ability to easily integrate other molecular
methodologies and accurate selection of colonies without missing or mixing colonies
are few more benefits.
Although classical
media serves as an inexpensive option financially, its results are less reliable.
The modern molecular biological approaches are very accurate but could be
costly and laborious. Chromogenic Agar falls in-between both these techniques
making it a middle cost and appropriately accurate option.
Initially
nobody including industries has showed interest in the Chromogenic medium
developed for E.coli in 1979, patented
by Dr. Rambach. Therefore he stopped his work in chromogenic field for 10 years
and he was more interested in genetic engineering. After 1989 he again
developed ‘Rambach Agar Salmonella’
for identifying Salmonella sp and ‘CHROMagar
E.coli’ for identifying E.coli.
More than three
decades after its invention, chromogenic agar caters to only 10% of the world’s
usage. Expansion of awareness among the microbiology
community will lead to the maximum utility of this technology.
References:
- http://ezinearticles.com/?How-Microbiologists-Use-Chromogenic-Agar-Media&id=3549221
- http://www.oxoid.com/UK/blue/prod_detail/prod_detail.asppr=CM1007&c=UK&lang=EN&org=124&img=CM1007C&sec=
- http://www.internationalpbi.it/docs/PBI/seminari/relazioni/Seminario-CHORMagar-PBI-AlainRambach.pdf
- http://www.chromagar.com/p-30_years_of_innovation.html?PHPSESSID=9f63481a27c30dc4a35d928f18c18482#.ULc9TuT28_h
- Z.Samra, M. Heifetz, J. Talmor, E. Bain and J. Bahar J. Clin. Microbiol. 1998, 36(4):990.
- http://www.internationalpbi.it/docs/PBI/seminari/relazioni/Seminario-CHORMagar-PBI-AlainRambach.pdf
- http://www.biosynth.com/index.asp?topic_id=137
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