Chapter 2 - 1.B - Different Purpose Media Flashcards
General-purpose Media
Those that will allow the growth of as broad a spectrum of microbes as possible. As a rule, they are of the complex variety. Examples include nutrient agar and broth, brain-heart infusion, and trypticase soy agar (TSA).
Enriched Medium
Contains complex organic substances such as blood, serum, hemoglobin, or special growth factors (Specific vitamins, amino acids) that certain species must have in order to grow.
Fastidious
Bacteria that require growth factors and complex nutrients.
Blood Agar
Made by adding sterile sheep, horse, or rabbit blood to a sterile agar base.
Selective Medium
Contains one or more agents that inhibit the growth of certain types of microbe or microbes, but not others. Selective media are very important in the initial stages of isolating a specific type of microorganism from samples containing dozens of different species-for example, feces, sliva, skin, water, and soil. They speed up isolation by suppressing the unwanted background organisms and favoring growth of the desired ones.
Media for isolating intestinal pathogens (MacConkey agar, Hektoen enteric [HE[ agar) contain bile salts as a selective agent. Other agents that have selective properties are dyes, such as methylene blue and crystal violet, and antimicrobial drugs.
Differential Media
Do not inhibit the growth of any particular microorganisms but are designed to display visible differences in how they grow. Differentiation shows up as variations in colony size or color, in media color changes, or in the formation of gas bubbles and precipitates. These variations often come from the type of chemicals these media contain and the ways that microbes react to them.
Reducing Medium
Contains a substance (Sodium thioglycolate or cystine) that absorbs oxygen or slows the penetration of oxygen in a medium, thus reducing its availability. Reducing media are important for growing bacteria that don’t require oxygen (termed anaerobic) or for determining the oxygen requirements of isolates.
Carbohydrate fermentation Media
Contains sugars that can be fermented (Converted to acids) and a pH indicator to show this reaction.
Transport media
Used to maintain and preserve specimens that have to be held for a period of time before clinical analysis or to sustain delicate species that die rapidly if not held under stable conditions.
Assay Media
Used by technologists to test the effectiveness of antimicrobial drugs and by drug manufacturers to assess the effect of disinfectants, antiseptics, cosmetics, and preservatives on the growth of microorganisms.
Enumeration Media
Used by industrial environmental microbiologists to count the number of organisms in milk, water, food, soil, and other samples.
Peptone
A soluble protein formed in the early stage of protein breakdown during digestion.
Protein hydrolysates formed by enzymatic or acidic digestion of various raw materials and many complex media contain peptones as the source of nitrogen
Hydrolysate
a substance produced by hydrolysis.
Chemically Defined Media
Termed Defined/Synthetic. Such media contain pure organic and inorganic compounds that vary little from one source to another and have a molecular content specified by means of an exact formula. Defined media may contain nothing more than a few essential compounds such as salts and amino acids dissolved in water or may be composed of a variety of defined organic and inorganic chemicals.
Useful for research applications when the exact concentration of components in the media is controlled so that the metabolic processes of the microbe can be precisely monitored.
Chemically complex media
contain extracts of animals, plants, or yeasts, including such materials as ground-up cells, tissues, and secretions. Examples are blood, serum, and meat extracts or infusions. These materials are sure to contain a rich supply of nutrients, although the type and amounts will vary from batch to batch-which is not a problem for many situations. Other possible ingredients are milk, yeast extract, soybean digests, and peptone.
