Screening For Common Diseases Using Chromogenic Media

Chromogenic media are used for applications which require the detection or enumeration of bacteria and other microbiological growth. These media are available as a granular material or as a powder which contain enzymes which react chromogenically with different types of microorganisms. The exact type of media chosen is dependent on the sort organisms whose presence is being tested for; the enzymes produced by the target population react with the substrate, causing a change of color. With customized incubation procedures, the selectivity of the application can be increased, often allowing for a confirmation of the target organism without any need for further testing.

Chromogenic media is a somewhat recent development in the life sciences, having first been used in the late 1980s when the possibilities of selective detection of microorganisms through chromogenic reactions came to be recognized. This procedure is often used as a simple test for the presence or absence of a particular microorganism, but along with other materials or by plating the media, they can also be used for the quantitative analysis of microbes.

It is color differentiation of this type of media which gives it an advantage over traditional types of culture media. Various types of bacterial colonies can be quickly identified through the distinctive hue or intensity of color that these organisms produce when in contact with chromogenic media. These media are used for easy identification of pathogenic microorganisms including Candida albicans, Staphylococcus aureus, Streptococcus B (used for screening for perinatal Group B Strep in infants) and all serotypes of Salmonella.

Due to the increase infections acquired in medical facilities and the rise of multiply resistant bacteria, these media are becoming an increasingly common item in clinics, hospitals and medical laboratories, with testing for nosocomial MRSA and Clostridium being especially important in clinical settings.

An especially important use for this type of media is for preliminary screening for common diseases; urinary tract infections, for one. These types of infections can be quickly tested for at clinics using plated chromogenic media, with Klebsiella, Enterobacter and E. coli among the organisms readily detectible in urine samples.

Testing for bacterial contamination in foodstuffs is another common application where chromogenic testing is useful; their ability to determine the presence of Staphylococcus aureus, Campylobacter, Salmonella, E. coli and other coliform bacteria and Listeria can all be tested for. Specific organisms can also be tested for using chromogenic analysis, making this an ideal method of ensuring the safety of the food supply.

Quite often, the media must be pre-enriched for at least 24 hours in order to allow the target organism to reach a high enough population to guarantee that these microbes will also be present in the chromogenic media when a subsample is taken for analysis. However, this is not always necessary, depending on the target organism, the type of media used and any other particular demands imposed by the application or environment, whether in water and food testing, screening for common infections or prenatal care. Chromogenic testing has become a valuable tool for quickly detecting potentially disease causing organisms and given the increase in dangerous antibiotic resistant microorganisms, is certain to take on an even larger role in medicine and the environmental sciences.