Media and Cultures (Unifinished)

Pure culture

composed of cells arising from a single progenitor (CFU); growth from only one type of bacteria present

Mixed culture

growth from 2 or more types of bacteria present; must be isolated prior to identification testing

Colony-forming unit (CFU)

used with urine cultures; each CFU= approximately 1,000 organisms which give the doctor an idea of the severity of infection

Streak-plate

an agar plate used for the isolation of bacteria. Inoculum is streaked over the agar surface to isolate individual colonies on the last quadrants of the plate

Pour-plate

method used for counting the number of microorganisms in a mixed sample which is added to a cooled molten agar medium prior to solidifying. Results in colonies uniformly distributed throughout the solid medium. Used to perform viable plate counts, especially in generating growth curves

Slant tubes

Test tube containing agar media that solidified while the tube was resting at an angle; screw-capped tube partially filled with agar & tilted at an angle when cooling resulting in a larger surface area for bacterial growth

Isolation (of bacteria)

the technique of separating one strain of bacteria from a mixed population

Incubation (of bacteria)

length of time plates are held & examined for growth or pathogens; minimum of 48 hours before being discarded

Petri plates (dishes)

shallow transparent lidded dish filled with media used to grow bacteria & molds

Defined media

​Also called synthetic media; exact chemical composition is known; fastidious organisms require the addition of a large number of growth factors

Complex media

Culturing medium with an unknown exact chemical composition because of partial digestion of nutrients (yeast, beef, soy, or proteins such as casein from milk) that release many different chemicals in a variety of concentrations each time it is made & due to the variety of nutrients available, it supports a wider variety of microorganisms; used to culture organisms with unknown nutritional needs

General purpose media

A routine culture media that microbiology laboratories use to cultivate a wide variety of microorganisms.

Selective media

Culturing medium containing substances that either favor the growth of particular microorganisms or inhibit the growth of unwanted ones; maybe selective when a single crucial nutrient is left out of it

Enrichment media

use of a selective media to increase the numbers of a chosen microbe to observable levels while inhibiting the growth or more abundant organisms may require a series of cultures to enrich for the desired microbe; cold enrichment used to enrich a culture with cold-tolerant species

Differential media

help microbiologists help differentiate between the various organisms growing on the surface

Anaerobic media

​obligate anaerobes must be cultured in the absence of free oxygen reducing media contain compounds that combine with free oxygen remove it from the medium

Transport media

used to ensure clinical specimens are not contaminated and to protect people from infection; rapid transport of samples is important

What are coliforms?

Gram-negative rods which can ferment lactose that are normally present in the digestive tract & found in feces; when found in drinking water, they are an indication of fecal contamination

If an organism “ferments” a carbohydrate, what does that mean?

The microorganism uses the carbs to produce energy to fuel their energy needs

What has happened to chocolate agar to make it look like chocolate?

The lysis of red blood cells in the media which release nutrients that aid in growth of fastidious organisms

What makes fastidious organisms unique?

Complicated nutritional requirements & won’t grow without specific factors present or in specific environmental conditions