9 21 notes (1).docx - Roberta Durham PDF

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Roberta Durham...

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Traditional growth media including Selective and/or Differential media are essential in the culture and identification of bacteria (classical approach). The more recent use of chromogenic substances (typically peptides that react with enzymes to yield a colored product) in bacteriological media has gained much attention. The product can be visually (easily) detected by direct observation of a distinct color change in bacterial colonies and sometimes, the medium itself. Advantages of chromogenic media include: 1. Faster results compared to traditional media- color reactions occurring within 24 h. 2. In some cases, visible detection is enough to satisfy identification. 3. Additional tests can be conducted using bacteria directly from the chromogenic medium. Researchers have discovered that one chromogenic substrate is very useful because several different enzymes react with it (i.e. specific to individual bacterial species) and as a result, different colored products occur based on those individual enzymes. For example, an enzyme produced by E. coli would react with the substrate to create a blue product, while a different enzyme produced by Salmonella would react to create a purple product.

This allows not just for identification but also for differentiation between different bacterial species. The chromogenic substrate is indoxyl substrate. Here is an example of a chromogenic medium and some reactions specific to three different bacterial species:

The next two labs for you will involve the use of chromogenic media to 1) determine the causative agent(s) of an individual’s urinary tract infection and 2) the causative agent(s) of food poisoning. You will be assigned a Case and have one week to complete the exercise. Your lab instructor will describe the media you will be using for each case.

Here are a few questions to test your understanding of the material: 1. What are the advantages of using chromogenic media to identify bacteria compared to using standard biochemical media that you used in lab for your unknown? a. Some advantages of using chromogenic media to identify bacteria include getting faster results occurring within 24 hours, visible detection is enough to satisfy identification in some cases, and additional tests can be done using bacteria directly from the chromogenic medium. 2. What is the definition of a chromogenic substance? Can you provide an example of one? a. A chromogenic substance is typically peptides that react with enzymes to yield a colored product. An example of one would be indoxyl substrate. 3. How quickly can you get an identification using a chromogenic medium? a. We can get the results from the chromogenic medium in 24 hours

Sometimes, confirmation of the identification you get from chromogenic media is needed. For example, if on a chromogenic medium you find you have E. coli, and you need to make sure it is E. coli, what would you do? Gram stain? TSI? Citrate? Mac? Yes, all of these can help. Mental cognition: Orientation - who you are and what is the environment around you Registration Attention and calculation

Mini-mental state examination (developed by Folstein, Folstein, McHugh) - Assess cognitive functions in number of clinical conditions, medical, or psychiatric - 5-10 min to complete - Initial assessment or even, serial measure - Max score - 30; 23-30 is normal -- 19-23 is borderline --...