CPA #7 Questions Flashcards
What is catalase?
an enzyme that coverts hydrogen peroxide to water and molecular oxygen
how do you test for catalase?
add a sample of bacteria to hydrogen peroxide; if it bubbles, catalase is present
what organisms DO NOT have catalase?
obligate anaerobes
why is nitrogen considered a growth-limiting nutrient?
they do not have enough nitrogen to build proteins and nucleotides; anabolisms stops
why are nitrogen fixers critical?
they provide nitrogen in a form that is useable by other organisms; change unusable N2 into usable NH3
define: nitrogen fixation
reduction of nitrogen gas to ammonia
explain the effect of temperature on proteins
if temp. is too high, a protein will denature and lose their shape and function because the hydrogen bonds break
explain the effect of temperature on lipids/phospholipids
if temp. is too low, the membranes of cells will become rigid/fragile; if temp. is too high, lipids can become too fluid and membrane cannot contain the cell/organelle
why are organisms sensitive to pH?
sensitive to changes in acidity; hydrogen ions interfere with hydrogen bonding within proteins and nucleic acids
how does the pH of the vagina and stomach reduce microbial infection?
the acidity of these areas inhibit microbial growth
why is cholera a concern in flooded areas?
Vibrio cholerae (causative agent) grows best outside of the body in water with pH of 9.0
why is water important to microbes? (3 reasons)
- require moist enviro. to be metabolically active
- water is needed to dissolve enzymes and nutrients
- water is a reactant in many metabolic reactions
why is osmotic pressure important?
restricts certain microbes to certain environments
define: obligate halophiles
grow under high osmotic pressure; high salty enviroments; will burst if in freshwater enviro.
define: facultative halophiles
do not require high salt enviro; able to tolerate the salty enviro; Staphylococcus aureus can tolerate up to 20% salt (allows it to colonize on human skin)
what type of relationship do biofilms represent?
complex synergistic (both sides receive greater benefits than if they were by themselves)
where would you find biofilms?
teeth, shower curtains, catheters, mucous membranes of digestive system
what percentage of bacterial diseases do biofilms contribute to?
70%
define: quorum sensing
when microbes respond to the density of nearby microbes; secrete quorum sensing molecules that communicate number and types of cells among the biofilm; how many other like bacteria are around to create a biofilm
minimum number needed to form a biofilm
what is a consequence of quorum sensing?
microbes become more harmful when they are a part of a biofilm; groups of bacteria are more dangerous
define: streak-plate method
an innoculating loop is used to streak a set pattern across a petri dish that gradually dilutes a sample to a point that CFUs are isolated from one another
define: CFU
colony-forming unit
list the 6 types of culture media
defined media, complex media, selective media, differential media, anaerobic media, & transport media
define: defined media
aka synthetic medium; the exact chemical composition is known
define: complex media
contains nutrients released by the partial chemical breakdown of yeast, beef, soy, or proteins
define: selective media
typically contain substances that either favor the growth of particular microbes or inhibit the growth of unwanted ones
define: differential media
formulated so that either the presence of visible changes in the medium or differences in the appearance of colonies help differentiate among bacteria
define: anaerobic media
stab culture; innoculating wire to the anoxic part of a medium; reducing media uses special anaerobic culturing conditions
define: transport media
carry clinical specimens of human bodily fluids/products in such a way to ensure that people are not infected and the sample is not contaminated
why do scientists refrigerate bacteria cultures?
to slow down the metabolism to prevent the accumulation of waste and the exhaustion of all nutrients in a medium
why do scientists sometimes freeze bacteria?
allows cultures to be restored years later
benefit of direct count
know exactly how many are present
con of direct count
time consuming
pro of indirect count
quick
con of indirect count
only an estimate; not exact
what are the 4 direct count methods
microscope counts
serial dilution and viable plate count
membrane filtration
flow cytometry
What are 4 indirect counts?
- dry weight
- turbidity & spectrophmeter
- PCR
- metabolic activity
counting 1 by 1
microscopic counts (direct)
pour liquid onto membrane to count
membrane filtration (direct)
count cells that glow
flow cytometry (direct)
weigh a pellet
Dry Weight (indirect)
cloudiness & amount of light that flows through
turbidity & spectrophotometer (indirect)
look for a specific band
PCR (indirect)
change in color
metabolic activity (indirect)
serial dilution & viable plate count (SD & VPC)
diluting sample until able to count individual (direct)
