Lab Test 1 Flashcards
Growth curve
represents an increase in cell numbers
typically includes four phases
Four phases of growth curve
lag phase
log phase
stationary phase
death phase
lag phase
inoculum is transfered to fresh medium
cells must adjust to new medium and synthesize full complement of enzymes
individual cells increase in size
log phase
cells divide, grow, and divide again
Each cell is divided into two cells
period of tremendous growth
generation time
The time it takes for a culture to double in size
stationary phase
culture exhausts the limited nutrients
division of cells slows, and the formation of new cells matches an equal amount of cell death
death phase
cell death rate exceeds any cell division
caused by accumulation of waste products and cell damage due to exposure to environment (light or chemicals)
What are the major atoms present in cells
CHNOPS
carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur
liquid media
nutrient broth
used to grow large numbers of organisms
solid media
used to examine morphology and help isolate organisms
what is most common solidifying agent
agar
Agar
a seaweed extract
polysaccharide
only melts at really high temp, once melted will remain liquid until cooled
is not digested by most microorganisms
complex media
non-synthetic or undefined
their exact chemical composition is not known
general purpose media
will support a wide range of organisms
used to grow dense cultures of bacteria, typically for experiments
Examples of general purpose media
nutrient broth
nutrient agar
tryptic soy broth
tryptone
peptone
soy extract
synthetic media
defined
made up of a strict list of inorganic compounds and carbon sources
what kind of organisms are incapable of growing on synthetic media
ones that rely on importing compounds from their environment
selective media
select for a certain type of microbe by supplying optimal conditions for growth
selects against potential competitors
What does Bromocresol purple broth (BPB) select for
enterococcus faecalis
Differential media
allow certain bacteria to be differentiated from others
typically by change in color or production of zone clearing
in many cases, they also include selective media to retard the growth of competitors
How is MacConkey Agar selective and differential
selects for Gram negative and against Gram positive
differential because color changes if lactose fermentation is present
exoenzymes
secreted by the cell into their environment
Three common exoenzymes
hydrolase
catalase
oxidase
hydrolytic enzymes (function)
break down complex molecules in their environments in order to obtain food for the cell
hydrolytic enzymes (types)
amylase
casease
gelatinase
amylase
catalyzes starch hydrolysis
Casease
hydrolyze milk proteins (casein) into peptides and ultimately amino acids
medium containing casein is often opaque
Gelatinase
hydrolyzes gelatin, a protein derived from collagen
catalase
enzyme that protects cell from hydrogen peroxide
hydrogen peroxide in the presence of catalase will produce water and oxygen
Oxidase
oxidase activity indicates the presence of cytochrome c
Cytochrome c
a component of some electron transport systems
pseudomonads are always oxidase…
positive
enteric bacteria are always oxidase…
negative
motile
can move under their own power
most common organelle for bacterial motility
flagellum
flagella
one or more long protein filaments that rotate to cause cell motion
T/F older cultures often do not exhibit motility
true
want to look at young cultures
Brownian motion
small particles are jostled by random collisions with water molecules
cells will move around randomly
how to tell if the cells are motile
move very quickly and in straight or curved paths
Motility Agar
semisolid- motile organisms can move through it
disadvantage of motility agar
if the organism is a strict aerobe it will only appear at surface and slightly away from stab line
It may appear that the organism is non-motile
Hanging Drop
views motility without the oxygen depletion and drying problems of wet mounts
