Micro Ch. 7, 7.5, & 8 Flashcards
microbial growth
*microbes grow larger only to divide into two new individuals.
*not defined by cell size, but by increase in the number of cells.
binary fission
cell division in bacteria (prokaryotes)
cell division
*cell duplicates its components & divides in two
*daughter cell becomes independent when the septum grows between them and they separate
*prokaryotes do not have a specific period of DNA synthesis, instead, in continuous dividing cells DNA synthesis is continuous
lag phase
*organisms do not increase significantly in number, but they are metabolically active and increase in size
*during this phase, organisms increase in size, produce large quantities of energy in form of ATP
*some adapt to new mediums in hours to days
log phase
*adapted to medium, population growth occurs at exponential rate
*growth appears as straight diagonal line on graph.
*growth at most rapid rate, interval called generation time.
*exponential growth occurs only for short time, then platueaus
stationary phase
*cell division decreases to the point that new cells are produced at the same rate as old cells die.
* straight horizontal line (plateau) on graph
*reasons for stationary phase: limited amount of nutrients may contain toxic quantities of waste material, or O2 supply becomes inadequate, pH changes may occur.
decline or death phase
*conditions become less supportive of cell division, cells lose their ability to divide, cells die.
*number of live cells decreased at logarithmic rate, straight downward diagonal on graph.
*cells undergo involution, assume variety of unusual shapes, difficult to identify.
*duration of phase highly variable. cultures of bacteria go thru all growth phases.
growth in colonies
*growth phases are displayed differently in colonies
*cell divides exponentially, forming colonies
*colony grows rapidly at its edges, cells in center grow more slowly/die (less nutrients/more waste)
*all phases of growth curve occur simultaneously in a colony, growth is non-synchronous
culturing bacteria
*technique was difficult to develop. early attempts isolate single cells by serial dilution, often unsuccessful because two or more organisms often present.
*Kochs technique of spreading bacteria over a solid surface was more effective “streak plate method”
streak plate method
*uses agar plates. *uses sterile wire to pick up bacteria. *move lightly along the agar surface. *depositing streaks of bacteria as you go. *the inoculating loop is flamed after streaking. *individual organisms are deposited in region streaked last. *after incubation, individual colonies derive from a single bacterial cell.
culture media
*many bacteria found growing together in oceans, lakes, soil & on living or dead organic material. (natural media)
*syphilis & leprosy, cannot be cultured in lab.
*lab media:
*synthetic media
*defined synthetic media
*complex media
*peptone
synthetic media
*prepared in lab with precise or reasonably well-defined composition
defined synthetic media
*contains known specific kinds and amounts of chemical substances, media that grows one specific type or species of bacteria
complex medium
*chemically non-defined medium, contains blood or extracts from beef, yeast, soybeans, other organisms. grows various types of species.
peptone
*enzyme digestion proteins. provides small peptides that microorganisms can use. trace elements and vitamins are present in sufficient quantities to support growth of many organisms.
casein hydrolaste
*made from milk protein, contains many amino acids and is used to enrich certain media.
blood agar
*useful in identifying organisms that can cause hemolysis, break down of red blood cells.
selective and differential media
*used to identify particular microorganisms, especially those from patients with infectious disease.
selective media
*one that encourages the growth of some organisms but suppresses the growth of others.
differential medium
*constituent that causes an observable change in the medium when a particular biochemical reaction occurs.
*allows for distinguishing a certain type of colony from others.
measuring bacterial growth (binary fission)
*measured by estimating the number of cells that have arisen by binary fission during growth phase
*measured by serial dilution or standard plate counts
serial dilution
*difficult to count more than 300 colonies on agar plate
*dilution of the bacteria before plating to know the volume of the culture.
*add 1ml of medium to 9ml sterile water 1:10dilution
*add 1ml of the 1:10dilution to 9ml of water 1:100dil.
*continue till we reach 10 to the 5th
*each dilution, culture on a agar plate using pour plate method or spread plate method
