Microbial Nutrition and Media Types

Study Notes

Production media require knowledge of microbial nutritional needs
Microbiologists have developed mediums based on years of experience
Some organisms, like those causing syphilis & leprosy, still need special media with living cells.
Many well-known organisms can be grown using various types of media.

Laboratory medias are usually synthetic, different from natural mediums.
Synthetic medias are created with precisely defined components in a lab setting.
Defined synthetic media use known amounts and kinds of chemicals.
Defined synthetic media examples are in tables 6.3 and 6.4.
Complex media, or non-chemically defined mediums use known, but variable materials. These can vary chemically batch to batch.

Many medias contain blood, extracts from beef, yeasts, soybeans, or other organisms.
Peptones (a product of enzyme digestion of proteins) are frequent ingredients.
Peptones supply small peptides for microbial use.
Complex media may have unknown trace elements and vitamins, yet still support numerous organisms' growth.
Complex medias include liquid broth and solidified agar.
Common lab media examples include "chocolate agar," which comes from cooked blood. It's used for fastidious organisms. Also, yeast extract provides vitamins, coenzymes, etc. and casein hydrolysate provides amino acids.

Media are generally categorized by physical state (liquid, semi-solid, solid).
Media are also based on their chemical composition (synthetic, complex).
Some medias have specific functions like general purpose, enriched, selective, and differential use.
Some media are used in enumerating, and for assays, etc .
Media can serve multiple functions.

Gelatin, while creating a reasonably solid surface, isn't as good as agar.
Gelatin can be digested by microbes and melts at warmer temps.
Nonliquefiable solid mediums (e.g., rice grains, cooked meat media, egg/serum) don't melt

Selective mediums contain compounds that inhibit the growth of specific microbes while allowing others to thrive.
These are very important for isolating individual microbes from complex mixtures found in samples.

Differential media used highlight differences in microbial growth.
Microbes reacting differently to their environments are visually represented (e.g., color changes, gas bubbles, precipitates)
These medias reveal how different microbes metabolize substances.
Some differential medias contain particular chemical substrates that lead to colored organisms.