microbial growth Flashcards
What is an exception to chromosome shaped bacteria
borrelia burgorferi (Lyme disease) is linear
What is the most common mechanism for replication for bacteria
Binary fission
What are the steps of binary fission
cell grows and increases size and cellular components
DNA replication
formation of division septum
cell separation
Where does DNA replication begin during binary fission
on the origin of replication where the chromosome is attached to the inner cell membrane moving in opposite directions
where does DNA replication end during binary fission
the terminus
how many daughter cells at the end of binary fission
2
what directs cytokinesis and cell division
protein FtsZ
what does FtsZ assemble into
a Z ring on the cytoplasmic membrane
What anchors the Z ring
FtsZ binding proteins
what does the Z ring define
the division plane between the two daughter cells
what happens when addition proteins are added to the Z ring
it forms the divisome
what does the divisome do
activates to produce a peptidoglycan cell wall and build a septum that divides the two daughter cells
what is the generation time in eukaryotes
time between the same points of life in two successive generations
what is another name for generation time in prokaryotes
doubling time
what is the generation time in prokaryotes
the time it takes for the population to double through one round of binary fission
what is the generation time of E. coli.
20 minutes
what is the generation time of tuberculosis
15-20 hours
what is the generation time of M. leprae
14 days
What is a closed culture
a culture where no nutrients are added and no waste is removed
what is an example of a closed culture in nature
a pond
what is culture density
the number of cells per unit volume
in a closed culture it is also the number of cells in a population
what are the phases of the growth curve
lag phase
log phase
stationary phase
death or decline phase
what is the lag phase
no increase in number of living bacterial cells
what is the lag phase
exponential increase in number of living bacterial cells
what is the stationary phase
plateau in number of living bacterial cell, rate of cell death and division are roughly equal
what is the death phase
exponential decrease in number of living bacterial cells
what happens to cells during the Lag phase
they grow larger, are metabolically active, synthesize proteins to grow. repair if damaged during transfer to medium
what do cells do during the log phase
they divide by binary fission
what is the intrinsic growth rate
generation time under specific growth conditions that are genetically determined
what are cells in the log phase used for
industrial purpose due to constant growth and uniform metabolic activity
when are bacteria most susceptible to disinfectants and antibiotics
the log phase
what factors contribute to a slowing growth rate
accumulation of waste products
used up nutrients
depletion of oxygen
what happens to cells in the stationary phase
synthesis of peptidoglycan, proteins, and nucleic acids slows, sporulation in bacteria that create endospores
what stage are antibiotics synthesized in
stationary phase
what cells are persisters in the death phase
those with a slow metabolic rate.
what makes persisters important
they are associated with certain chronic infections such as TB, that do not respond to abx treatment.
what is an industry that keeps bacteria in a log phase
microbial production
what is a chemostat used for
to maintain a continuous culture where nutrients are supplied at a steady rate, a controlled amount of air is added and bacterial suspension is removed at the same rate as nutrients flow in to maintain an optimal growth environment
what does bacterial count indicate
the extent of an infection
what is the direct cell count method
counting cells in a liquid culture or colonies on a plate
what is the direct microscopic cell count
transferring a known volume of a culture to a calibrated slide and counting cells under a microscope (simplest way)
what is a petrol-hausser chamber
the calibrated slide used in direct microscopic cell count
what is the advantage of a petrol-hausser chamber
its easy to use
relatively fast
inexpensive
does not work well with dilute cultures because their mayn’t be enough cells to count
what are the cons of a chamber
does not necessarily yield an accurate count of live cells
can’t tell difference between living and dead cells
what does a Coulter counter do
detects the changes in electrical resistance in a saline solution. as a cell passes by the change in resistance is measured and the cell ocunged
what if a sample in Coulter counter is too dense
more than one cell may pass by at one time and not be counted properly skewing results,
does Coulter counter distinguish between live and dead cells
no
what is a plate count
counting colony forming units after incubation
what are the cons of a plate count
more than one cell may give rise to a colony
those that grow in clusters or chains are hard to disperse, a single colony may be many cells
some cells are viable but nonculturable
how many colonies on a typical plate
30-300
what happens if there are less than 30 colonies
it is not statistically reliable
what happens with colonies over 300
overcrowding making it difficult to count
how is a serial dilution made
1ml of culture is added to 9ml of sterile broththe process is continued until until the desired concentration is reached
what happens after dilution is complete
from each tube a sample is plated using pour plate method spread plate method and incubated until colonies appear
how many plates made for each dilution
2-3
What are the steps of the pour plate method
bacterial sample is mixed with agar
sample is our onto sterile plate
sample is swirled Tomis and allowed to solidify
plate is incubated
what are the steps of the spread plate method
sample is poured onto a solid medium
spread sample evenly over the surface
plate incubated until colonies grow
what is the membrane filtration technique
a modified plate count technique that concentrates a sample rather than diluting.
how does membrane filtration technique work
known volumes are vacuum filtered aseptically through membrane with a pore small enough to trap organisms and then transferred to a petri plate
how is calculation of cell density made from membrane filtration technique
dividing the cell count by volume of filtered liquid
What is most probable number
a statistical procedure for estimating the number of viable microorganisms in a sample
what is the best method for counting bacteria in water
membrane filtration technique
what is the most probable number method used for
water and food sampels
what does the MPN method evaluate
detectable growth by observing changes in turbidity or color due to metabolic activity
what is a typical application of MPN method
estimating coliforms in pond water
what are coliforms
gram-negative rod bacteria that ferment lactose
what is the presence of coliforms a sign of
contamination by fecal matter
how does the MPN method work with pond water
three dilutions of water is tested by inoculating five lactose broth tubes with 10ml of sample, 5 lactose broth tubes of 1ml and 5 lactose broth tubes of 0.1ml of sample with a ph indicator in the tube
what color on the ph indicator indicates fermentation
yellow
what do indirect cell counting methods use to estimate number
cell density
what is the most common indirect cell count
measuring turbidity
what is turbidity
cloudiness
what is a spectrophotometer
an instrument used to measure turbidity
what happens to turbidity as bacterial cell count increases
turbidity increases and less light can reach the detector
what is measuring the dry weight of a sample
another indirect method of evaluating culture density
what must happen before a dry weight of a sample is taken
the sample must be concentrated, washed and dried
what is the dry weight method good for
filamentous microorganisms
what is fragmentation
when many nucleotides accumulate in an enlarge round cell or along a filament and many new cels split from the parent filament and float away
what is a bacteria that does fragmentation
cyanobacteria and actinomycetes
describe actinomycetes
gram-positive, anaerobic bacteria found in soil.
what is budding
, a form of reproduction of where an organism forms a long narrow extension whose tip swells and forms a smaller cell that detaches.
where does budding occur
most commonly in yeast but in some posthecate bacteria and cyanobacteria
what are biofilms
ecosystems that form on a variety of surfaces in a liquid environment
what are filamentous biofilms called
streamers
where do filamentous biofilms form
in rapidly flowing water such as streams eddies and specially designed laboratories
how are streamers anchored to the substrate
by a head while the tail floats down stream
what shape do biofilms take in slow moving water
a mushroom-like shape
what is the extracellular matrix in a biofilm made of
extracellular polymeric substances secreted by the organisms of the biofilm
what percent of the biofilm is extracellular matrix
50-90 percent of the total dry mass
what is EPS
a hydrated gel composed of polysaccharides and other macromolecules
what does EPS do
maintains integrity and function of the biofilm
what are planktonic cells
free-floating microbial cells in an aquatic environment
how is a biofilm formed
a plankton cell attaches to as substrate
first colonizers become irreversibly attached
growth and cell division
production of EPS and formation of water channels
attachment of secondary colonizers and dispersion of microbes to new sites
what is an example of a metabolic collaboration in a biofilm
aerobic microorganisms consume oxygen, creating anaerobic regions to promote growth of anaerobes
what is the mechanisms where cells in a biofilm coordinate their activities
quorum sensing
what does quorum sensing do
enables microorganisms to detect their cell density through the releasing and binding autoinducers
what do gram negative bacteria communicate using
N-acylated homoserine lactones
what do gram positive bacteria use to communicate
small peptides
when did oxygen begin rising on earth
when cyanobacteria started producing it and irons capacity for taking it up was exhausted
What are some environments that are molecular oxygen free
deep ocean
earths crust
marshes
bogs
sewers
in parts of animal bodies
what does a thioglycolate tube culture test for
different requirement of molecular oxygen
what does autoclaving due to thioglycolate
flushes out most of the oxygen
how does a thioglycolate tube culture work
the tube is autoclaved, inoculated and cultured at the appropriate temperature.
as oxygen diffuses bacterial density increases where the oxygen concentrations is best suited for growth
in a thioglycolate tube culture what type of bacteria grow best at the top of the tube
obligate strict aerobes
what type of bacteria grow at the bottom of a thioglycolate tube culture
obligate anaerobes that will likely be killed by oxygen
what grows at the top of the tube and through out the tube
facultative anaerobes
what is a facultative anaerobe
an organism that thrives I oxygen but also grows in its absence relying on fermentation or anaerobic respiration.
what kind of organism grow uniformly throughout the tube
aerotolerant anaerobes, the are indifferent to oxygen and have a fermentative metabolism
where do microaerophiles gather in the tube
just below the surface
what are the oxygen requirements for microaerophiles
1-10 percent
examples of obligate aerobes
mycobacterium tuberculosis
micrococcus luteus
neisseria meningitidis
n. gonorrhoeae
what type of bacteria make up a large portion of the gut
obligate anaerobes mainly bacteroidetes
what are transient anaerobic conditions
when tissues are not supplied with blood circulation and die breeding obligate anaerobes
obligate anaerobes that cause infections in humans
C. diff
c. tetani
c. perfringens (gangrene)
what is the most common way to grow obligate anaerobic bacteria
in an anaerobic jar that has chemical packs that remove oxygen and release carbon dioxide
what is an anaerobic chamber
an enclosed box where all oxygen is removed
name two examples of facultative anaerobes
staphylococci
enterobacteriaceae
what do the presence of facultative anaerobes lead to
an environment for obligate anaerobes thrive
what are some examples of aerotolerant anaerobes
lactobacilli
streptococci
what is an example of a microaerophil
campylobacter jejuni
what is minimum permissive oxygen concentration
the lowest concentration of oxygen that allows growth
what is maximum permissive oxygen concentration
the highest tolerated concentration of oxygen
what does. aerobic respiration generate
reactive oxygen species, byproducts that must be detoxified
what enzymes break down ROS
superoxide dismutase
peroxidase
catalase
what does peroxidase oxidize
hydrogen peroxide or other peroxides into water
what does superoxide dismutase break down
superoxide anions generated by aerobic metabolism
what does catalase breakdown
hydrogen peroxide to water and oxygen
what detoxification enzymes do obligate anaerobes have
none
what detoxification enzymes do aerotolerant anaerobes have
superoxide dismutase
what are capnophiles
bacteria that grow best with high CO2 and low oxygen
how do you grow capnophiles
a candle jar
what is a candle jar
a jar with a tight lid that can accommodate the cultures and a candle. the candle burns out most oxygen and releases CO2
what gives yogurt, pickles, and lime seasoned dishes the tangy taste
acid content
what happens to macromolecules at a high ph
hydrogen bonds holding DNA break
lipids are hydrolyzed
concentration gradient collapses and impairs energy production
hydrogen bonding in amino acid functional groups is broken down
what is optimum growth PH
the most favorable PH for growth of an organism
what is minimum growth ph
the lowest ph an organism can candle.
what is a maximum growth PH
The highest PH an organism can grow in
what is the optimal growth ph of salmonella
7.0-7.5
what is a neutrophile
a bacteria that grows at a pH within one two ph units of neutral
examples of neutrophiles
e. coli (minus some strains)
staphylococci
salmonella
bacteria that dont do well in stomach acid
some e. coli
s. typhi and other intestinal pathogens
what ph do fungi thrive at
5-6
what are acidophiles
microorganisms that grow optimally at a ph of less than 5.55
examples of acidophiles
sulfolobus
ferroplasma
lactobacillus
what ph do sulfolobus survive at
2.5-3.5
what ph do ferroplasma live in
0-2.9
what ph does lactobacillus live at
3.5-6.8
what adaptations do organisms make to live at a low pH
proteins have increased negative surface charge to stabilize them
what are alkaliphiles
microorganisms that grow best at a ph of 8-10.5
examples of alkaliphiles
vibrio cholera
matron-bacterium
bacillus firmus
what ph does cholera grow best at
8-10.5
grows better at 8 but can survive up to 11 and inactivated by stomach acid
what pH does natronobacterium grow best at
10.5
what adaptations do extreme alkaliphiles have
modifications lipid and protein structure and compensatory mechanisms to maintain proton motive
higher isoelectric point due increase in amino acids
what is a mesophile
an organisms that likes moderate temperatures 20-45C
what are examples of mesophile
human microbiota Ecoli, salmonella, lactobacillus
what are psychotrophs
prefer cooler environments 4-25C
what are psychotrophs responsible for
food spoilage of refrigerated food
what is a psychrophile
cold loving organism 0C-15C
what are thermophiles
organisms that grow from 50C to 80C
examples of thermophiles
thermos aquaticus
geobacillus
what’s a hyperthermophile
organisms that grow in 80-110C
examples of hyperthermophiles
pyrobolus
pyrodictium
effects of low temperature on macromolecules
membranes lose fluidity and damaged by ice crystal formation
chemical reactions slow
proteins too rigid to catalyze reactions and may denature
how does heat affect macromolecules
denatures proteins
increases fluidity
how have proteins in psychrophiles adapted
increase flexibility
lower number secondary stabilizing bonds
may have antifreeze proteins
unsaturated lipid membranes to increase fluidity
adaptations in thermophiles and hyperthermophiles
increased ratio saturated to polyunsaturated lipids to limit fluidity
DNA has higher guanine-cytosine bases
replacement of key amino acids to stabilize folding
what are halophiles
salt loving organisms that require high salt concentrations
what are practical applications of thermoenzymes
degradation enzymes are added as ingredients in hot-water detergent increasing effectiveness
what is the salt concentration of marine environments
3.5%
examples of halophiles
red alga dunaliella salina
halobacterium
what is the salt concentration of the great salt lake
3.5-8X saltier than the ocean
what is the salt concentration of the dead sea
10x the ocean
how does dunaliella counter osmotic pressure
which a high cytoplasmic concentration of glycerol and by pumping out salt ions
how does halobacterium counter osmotic pressure
by accumulating large concentrations K and other ions in the cytoplasm
what are halo tolerant organsism
tolerate salt but dont need it for growth
example of halo tolerant organisms
halomonas
staphylococci
micrococci
corynebacteria
s. aureus
bacillus cereus
v cholerae
what bacteria cause food born illness because of their ability to reproduce in food
s. aureus
bacillus cereus
cholerae
what is moisture measured as
water activity
what is water activity
the ratio of the vapor pressure of the medium of interest to the vapor pressure of distilled water
bacteria vs fungi water requirements
water requires more fungi requires less
what are ways of decreasing water content to prevent spoilage
drying like jerky, freeze drying, making brine and jams
what are barophiles
organisms that require high atmospheric pressure
where is large atmospheric pressure found
bottom of the ocean
what is an example of an all-purpose media
tryptic spy broth
what does enriched media contain
growth factors, vitamins, and other essential nutrients to promote growth of fastidious organisms
what is a fastidious organisms
organisms that cannot make certain nutrients and need them added to the medium
what is a chemically defined medium
when the complete chemical composition a medium is known
what is an example of a chemically defined medium
EZ medium
what is complex media
contains extracts and digests of yeasts meat or plants and the precise composition is not known
examples of complex media
nutrient broth
tryptic soy broth
bran heart infusion
what does non-selective media do
supports the growth of all microorganisms without any specific inhibition
what is non-selective media used for
to cultivate organisms for other uses and in specific procedures
what is an example of a non-selective media
mueller-hinton agar
what is mueller Hinton agar used for
to test antibiotics like in the Kirby Bauer disc diffusion test
what does mueller Hinton agar contain
beef extract, agar, starch
what does starch do for mueller-hinton agar
supports growth, absorbs toxins and ensures abx will continue to function
what are selective media
media that inhibits growth of unwanted microorganisms and support growth of the organism of interest
how do selective media work
by supplying nutrients and reducing competition
What is an example of a selective media
macconkey agar
what does macconkey agar contain
bile salts and crystal violet that interfere with the growth of gram-positive bacteria in favor of gram negative bacteria, particularly Enterobacteriaceae
what do enrichment cultures do
foster preferential growth of a desired microorganism that represents a fraction of the organisms present in an innocculum
ex bacteria that eat crude oil
what does differential media do
make it easy to distinguish colonies of different bacteria by a change in color of the colonies or color of the medium
what makes color changes in differential media
the result of end products created by interaction of bacterial enzymes with differential substrates or lysis of red blood cells
what can be observed on macconkey agar
differential fermentation of lactose
what color does lactose fermenters turn macconkey agar
hot pink due to the acid interacting with indicator neutral red
Which of the following methods would be used to measure the concentration of bacterial contamination in processed peanut butter?
total plate count
In which phase would you expect to observe the most endospores in a Bacillus cell culture?
death phase
During which phase would penicillin, an antibiotic that inhibits cell-wall synthesis, be most effective?
log phase
Which of the following is the best definition of generation time in a bacterium?
the length of time it takes for a population of cells to double
If a culture starts with 50 cells, how many cells will be present after five generations with no cell death?
1600
Filamentous cyanobacteria often divide by which of the following?
fragmentation
Which is a reason for antimicrobial resistance being higher in a biofilm than in free-floating bacterial cells?
Cells are metabolically inactive at the base of a biofilm.
Quorum sensing is used by bacterial cells to determine which of the following?
density of the population
Which of the following statements about autoinducers is incorrect?
They bind directly to DNA to activate transcription.
An inoculated thioglycolate medium culture tube shows dense growth at the surface and turbidity throughout the rest of the tube. What is your conclusion?
The organisms are facultative anaerobes.
Pseudomonas aeruginosa is a common pathogen that infects the airways of patients with cystic fibrosis. It does not grow in the absence of oxygen. The bacterium is probably which of the following?
an obligate aerobe
Why do the instructions for the growth of Neisseria gonorrhoeae recommend a CO2-enriched atmosphere?
It is a capnophile.
Bacteria that grow in mine drainage at pH 1–2 are probably which of the following?
acidophiles
Bacteria isolated from Lake Natron, where the water pH is close to 10, are which of the following?
alkaliphiles
In which environment are you most likely to encounter an acidophile?
a hot vent at pH 1.5
A soup container was forgotten in the refrigerator and shows contamination. The contaminants are probably which of the following?
psychrotrophs
Bacteria isolated from a hot tub at 39 °C are probably which of the following?
mesophile
In which environment are you most likely to encounter a hyperthermophile?
hydrothermal bent at the bottom the ocean
Which of the following environments would harbor psychrophiles?
mountain lake with a water temperature of 12 °C
Which of the following is the reason jams and dried meats often do not require refrigeration to prevent spoilage?
low water activity
Bacteria living in salt marshes are most likely which of the following?
Halotolerant
Haemophilus influenzae must be grown on chocolate agar, which is blood agar treated with heat to release growth factors in the medium. H. influenzae is described as ________.
fastidious
Direct count of total cells can be performed using a ________ or a ________.
hemocytometer, Petroff-Hausser counting chamber
The ________ method allows direct count of total cells growing on solid medium.
plate count
A statistical estimate of the number of live cells in a liquid is usually done by ________.
most probable number
For this indirect method of estimating the growth of a culture, you measure ________ using a spectrophotometer.
turbidity
Active growth of a culture may be estimated indirectly by measuring the following products of cell metabolism: ________ or ________.
ATP, acid from fermentation
A bacterium that thrives in a soda lake where the average pH is 10.5 can be classified as a(n) ________.
alkalophile
Lactobacillus acidophilus grows best at pH 4.5. It is considered a(n) ________.
acidophile
A bacterium that thrives in the Great Salt Lake but not in fresh water is probably a ________.
halophile
Bacteria isolated from the bottom of the ocean need high atmospheric pressures to survive. They are ________.
barophiles
Staphylococcus aureus can be grown on multipurpose growth medium or on mannitol salt agar that contains 7.5% NaCl. The bacterium is ________.
halotolerant
Blood agar contains many unspecified nutrients, supports the growth of a large number of bacteria, and allows differentiation of bacteria according to hemolysis (breakdown of blood). The medium is ________ and ________.
complex, differential
