How Microbiologists Use Chromogenic Agar Media

Standard growth media in the microbiology laboratory has been advancing in its development over the decades since the late 1800s, when agar was discovered by the use of extracts from red seaweeds, a gelling agent used also in making jellies. Agar is still in use today, and its use has not changed much over the decades. The many things that have changed are the chemicals and infusions used to create specialized growth media that is both selective and identifying: Chromogenic agar media.

Chromogenic agar media is a highly specialized growth medium for microbiologists to aid in the isolation and identification of certain types of pathogenic microorganisms. Many pathogenic organisms are also fastidious, difficult to grow on standard agar plates without enrichment of some sort. The use of broths for the proliferation of certain fastidious organisms is a technique that has not changed much in recent years, as it is a proven method for the enrichment of the organisms prior to agar plate inoculation.

Broths have a certain amount of nutrients to stimulate the propagation of a specific organism so there would be an abundance of living material to work with in the lab. Beef and brain extracts in broths can cause a dramatic escalation of organisms prior to inoculation of chromogenic agar media, so there is no doubt that there will be success after timed incubation.

When the enriched organism is available, inoculation of the chromogenic media follows, in the standard practice using aseptic techniques. After an incubation period of 18-24 hours, the agar plate is analysed for colony growth, colony count, colony morphology, which includes colony colour. This is vital for the positive identification of the specific organism being researched or diagnosed. Selective media like chromogenic agar can be specialized for a variety of fastidious and hard to identify bacteria strains.

There is a diversity of chromogenic agar media available to the microbiologists today. One such important media is MRSA identification media. Methicillin-resistant Staphylococcus Aureus is an organism that has been wreaking havoc in the populations of major countries, as well as undeveloped countries. This organism causes illnesses such as toxic shock syndrome or staph infections of skin, eye, and wounds. It is difficult to identify considering the other organisms that may contaminate or proliferate during the culturing process.

Hospitals and nursing care facilities have been attempting to isolate patients diagnosed with the harmful pathogen, and immediate identification is not only encouraged, but also necessary. Specialized chromogenic agar media is used for this, as it leaves no doubt of the identity of the organism if present. The selective agar has color indicators for easy morphological identification, as well as specialized inhibitors to screen out undesirable normal flora from interfering with the isolation techniques.

Chromogenic agar media is also used in the isolation and identification of gram-negative pathogens like Neisseria spp., which can cause not only meningitis in children, but can also be blamed for the spread of sexually transmitted disease throughout a community. Specialized growth media not only isolates the growth of these highly fastidious organisms, but inhibits the growth of less fastidious organisms as well. The chromogenic action of the agar makes identification more efficient also, as the colonies of Neisseria species have exclusive colour. Chromogenic agar media is the gold standard for the identification and analysis of pathogenic fastidious bacteria.