Media, Methods of Isolation, & Aseptic Transfer Flashcards
Selective Media
favors growth of ONE group of micro-organisms & inhibits growth of others - usually gram - or +
Differential Media
Allows you to distinguish among the bacteria in a sample by there ability to utilize certain substrates or perform certain reactions
Contains an indicator to detect presence or absence pf specific metabolic activity (e.g. lactose fermenters) which is usually indicated by a color change (allows for distinguishing among types)
Mixed & Pure Cultures
mixed cultures consist of two or more species
pure cultures consist of only ONE species
Coliform bacteria
normally found in large intestine or aquatic environments, soil, and on vegetation
universally present in feces of warm-blooded animals
bacterial indicator of sanitary quality of food & waater
Coliform bacteria includes
E. coli (fecal coliforma) , Enterobacter, & Serratia
Presumptive Identification
Tentative identification of an isolate based on one or more key test results
CFU (Colony Forming Unit)
general term used to describe the origin of a colony
e.g. some colonies form from individual cells & others from pairs, chains, or cluster of cells
Growth Media
Common media used for maintaining bacterial cultures
Must meet the diverse nutrient requirements of routinely cultivated bacteria
Types of growth media
General-purpose media
Enriched media
Selective and differential media
Undefined (complex) media
General-purpose media
used to cultivate microbes
e.g. trypticase say agar
Enriched media
contains special growth factors that certain species must be provided to grow
Selective and differential media
used in identification of microbes
Undefined (complex) media
the exact composition and amounts of carbon and nitrogen are not known
Forms of media
nutrient broth and nutrient agar
Nutrient broth
liquid form
Nutrient agar
solid form
agar slate, agar deep, & agar plate (Petri dish)
Agar slants
allowed to cool and solidify on an angle
Agar deeps
allowed to cool and solidify in upright position
Agar plate (Petri dish)
a lid is used to prevent airborne contamination
plates must be stored or incubated upside down to prevent condensation droplets that may form on the lid
Aseptic transfer technique
techniques utilized during transfer of sample (inoculum) to sterile culture medium
prevent contamination of sample (source), sterile culture medium, or surroundings
Inoculating loops
used to smear, streak, or retrieve an inoculum from a culture of micro-organisms
Identify whole colony features
round
irregular
spindle
filamentous
rhizoid
Identify margin features
smooth
irregular (erose)
lobate
filamentous (filiform)
rhizoid
Aseptic transfer from broth to broth
Aseptic transfer from broth to slant
Aseptic transfer from source plate to sterile agar plate (streak plate method of isolation)
Note for streaking
during streaking, the cell density decreases, eventually leading to individual cells being deposited separately on the agar surface
cells that have been sufficiently isolated will grow into colonies consisting ONLY of the original cell type
Identify
Completed streak plate
Each streak takes a little from the previous quadant, spreads it to the next and then transfers some to the next before finally spreading in the 4th quad for isolated colonies
Thickest growth occurs in the first quadrant streak and isolated colonies occur on the fourth quadrant streaked
Step #1 (thickest growth)
Step #2
Step #3
Step #4 (isolated colony)
