Chap 6 Flashcards
Physical requirements for microbial growth
- Temperature
- pH
- Osmotic pressure
Chemical requirements for growth
- Carbon
- N,S,P
- trace elements
- Oxygen
- Organic growth factors
Types of temperatures involved in growth
Minimum growth temperature
Optimum growth temperature
Maximum growth temperature
Psychrophiles
cold-loving
Mesophiles
Moderate temperature loving
Thermophiles
heat-loving
Psychrotrophs grow between which temperatures?
0 C and 20-30 C
Psychotrophs cause
food spoilage
Refrigerator temperatures
40 to 40 F
Many bacteria survive, some may grow
40 F to 60 F
Danger zone temp range
60 F to 130 F
Very slow bacterial growth
50-60 C
Temperatures in this range destroy most microbes, although lower temperatures take more time
above 60 C
Thermophiles optimum growth temperature
50-60C
Thermophiles are found in
hot springs and organic compost
Hyperthermophiles optimum growth temperature
above 80C
Most bacteria grow between what pH range?
6.5-7.5
Molds and yeasts grow between what pH range?
5 and 6
Acidophiles grow in what environments
acidic
What is plasmolysis?
the process of water leaving plant cells, allowing the cytoplasm and plasma membrane to shrink away from the cell wall.
What causes plasmolysis?
hypertonic environments; high osmotic pressure
Extreme or obligate halophiles require what kind of osmotic pressure?
high osmotic pressure (high salt)
Faculative halophiles tolerate what?
high osmotic pressure
Why are hyperthermophiles that grow at temperatures above 100C seemingly limited to oceanic depths?
the extreme pressure at those depths allows water to remain liquid at such high temperatures, which is necessary for their survival; essentially, the high pressure counteracts the boiling point of water, enabling them to exist in a liquid environment where they can function properly.
Other than controlling acidity, what is an advantage of using phosphate salts as buffers in growth media?
primary advantage of using phosphate salts as buffers in growth media is that they provide a readily available source of phosphorus, an essential nutrient for most bacteria, making them non-toxic and beneficial for microbial growth.
Why might primitive civilizations have used food preservation techniques that rely on osmotic pressure?
Growth of the cell is inhibited as the plasma membrane pulls away from the cell wall. The high salt or sugar concentrations draw water out of any microbial cells, thus prevent their growth.
Name each of the four elements needed in large amounts for microbial growth.
carbon, nitrogen, sulfur, and phosphorus
Identify ways in which aerobes avoid damage by toxic forms of oxygen
produce enzymes such as catalase, peroxidase and/or superoxide dismutase that break down toxic forms of oxygen and their intermediate byproducts.
Function of carbon
Structural backbone of organic molecules
Chemoheterotrophs use organic molecules as
energy
Autotrophs use
CO2
Nitrogen is a component of
proteins, DNA & ATP
Most bacteria decompose protein material for the
nitrogen source
Some bacteria use NH4+ or NO3- from
organic material
A few bacteria use what in nitrogen fixation?
N2
Sulfur is used in
- Amino acids,
- Thiamine
- Biotin
Most bacteria decompose protein for the
sulfur source
Some bacteria use SO4 2- or H2S
true
Usage of phosphorus
DNA, RNA, ATP
Phosphorus is found in
membranes
What is a source of phosphorus?
PO4 3
What are trace elements?
Inorganic elements required in small amounts
Trace elements usually function as
enzyme cofactors
Examples of trace elements
iron, copper, molybdenum, and zinc
Obligate aerobes+
require oxygen
Facultative anaerobes
grow via fermentation or anaerobic respiration when oxygen is not available
Anaerobes
unable to use oxygen and most are harmed by it
Aerotolerant anaerobes
tolerate but cannot use oxygen
Microaerophiles
Require O2 concentration lower than air
Growth of obligate aerobes
Growth on top. Growth occurs where high concentrations of oxygen have diffused into the medium
Faculative anaerobes
Growth
Growth is most concentrated on top, but some is into the medium. Growth is best where most oxygen is present, but occurs throughout the tube.
Growth of obligate anaerobes
Growth occurs only where there is no oxygen. At bottom of broth.
Aerotolerant anaerobes growth
growth occurs evenly, oxygen has no effect
Singlet Oxygen
boosted to a higher-energy state and is reactive. 1O2 -
Superoxide radicals
O2
Superoxide radicals equation
O2- + O2- + 2H+ —> H2O2 + O2
Peroxide anion
O2 2-
Peroxide Anion equation
2H2O2 —> 2H2O + O2
H2O2 + 2H+ —> 2H2O
Hydroxyl radical
OH -
OH.
Organic compounds are obtained from the
environment
Examples of organic growth factors
- Vitamins,
- amino acids,
- purines,
- pyrimidines
If bacterial cells were given a sulfur source containing radioactive sulfur (35 S) in their culture media, in what molecules would the
35 S be found in the cells?
Bacterial cells would incorporate the radioactive sulfur (35S) into amino acids, proteins, and nucleic acids in their cells
How would one determine whether a microbe is a strict anaerobe?
culture it in an oxygen-free environment and observe if it grows well; if the microbe only grows in the absence of oxygen, it is considered a strict anaerobe
Oxygen is so pervasive in the environment that it would be very difficult for a microbe to always avoid physical contact with it. What, therefore, is the most obvious way for a microbe to avoid damage?
Produce enzymes that would neutralize them from toxicity
What are biofilms?
Microbial communities
Biofilms form
slime or hydrogels that adhere to surfaces
How do bacteria in biofilms communicate?
Bacteria communicate cell-to-cell via quorum sensing
quorum sensing
a cell-to-cell communication process that allows bacteria to sense their population density and adjust their gene expression
How do bacteria use quorum sensing to communicate?
Bacteria secrete an inducer (signaling chemical) to attract other bacterial cells
In biofilms, bacteria share
nutrients
In biofilms, the bacteria can be sheltered from
harmful environmental factros
Where can you find biofilms?
digestive system and sewage treatment systems, can clog pipes
How resistant are biofilms to microbicides?
1000x resistant
Biofilms are involved in what perecentage of infections?
70%
Common sites of infections
Catheters, heart valves, contact lenses, dental caries
Identify a way in which pathogens find it advantageous to form biofilms.
- Antibiotic resistance
- Protection from immune system
- Nutrient trapping (concentrated source of food within)
- adhesion to surfaces
- quorum sensing that allows the group to respond to environmental clues
Culture medium
nutrients prepared for microbial growth
Sterile
no living microbes
inoculum
introduction of microbes into a medium
Culture
microbes growing in or on a culture medium
Agar is made of
Complex polysaccharide
Agar is used as
solidifying agent for culture media in Petri plates, slants, and deeps
Agar liquifies at what temp
100 C
Agar solidifies at what temp
approx 40 C
What is chemically defined media?
exact chemical composition is known
Fastidious organisms
those that require many growth factors provided in chemically defined media
Complex media
extracts and digests of yeasts, meat, or plants; chemical composition varies batch to batch
Examples of complex media
- Nutrient broth
- Nutrient agar
Reducing media is used for
the cultivation of anaerobic bacteria
Reducing media contains
chemicals that combine O2 to deplete it (Sodium Thioglycolate)
Reducing media is heated to
drive off O2
Capnophiles
Microbes that require high CO2 conditions
Things needed to culture canophiles
1.CO2 packet,
2. candle jar
B S L - 1
no special precautions; basic teaching labs
BSL-2
lab coat, gloves, eye protection
BSL-3
biosafety cabinets to prevent airborne transmission
BSL-4
sealed, negative pressure; “hot zone”
In BSL-4, the exhaust air is
is filtered twice through H E P A filters
Selective media purpose
- Suppress unwanted microbes and encourage desired microbes
- Has inhibitors to suppress growth
Differential media allows for
distinguishing of colonies of different microbes on the same plate
Some media have both selective and differential characteristics
True or false?
True
What is an enrichment culture?
Encourages the growth of a desired microbe by increasing very small numbers of a desired organism to detectable levels
An enrichment culture is usually which state of matter?
liquid
Growth of chemoautotrophs and photoautotrophs; microbiological assays
chemically defined media
Growth of most chemoheterotrophic organisms
complex media
Growth of obligate anaerobes
reducing media
Suppression of unwanted microbes; encouraging desired microbes
selective media
Differentiation of colonies of desired microbes from others
Differential media
Similar to selective media but designed to increase numbers of desired microbes to detectable levels
Enrichment media
Could humans exist on chemically defined media, at least under laboratory conditions?
Yes, under laboratory conditions, human cells can exist and even proliferate on chemically defined media, meaning a medium where all the chemical components are known and precisely controlled; Has nurteints, can’t grow a whole organsim though
Could Louis Pasteur, in the 1800s, have grown rabies viruses in cell culture instead of in living animals?
No, viruses only reproduce in a living host cell
Pure culture
Contains only one species or strain
Colony
population of cells arising from a single cell or spore or from a group of attached cells
Colony Forming unit
unit used in microbiology to estimate the number of viable microorganisms in a sample
Streak plate method
Used to isolate pure cultures
Can you think of any reason why a colony does not grow to an infinite size, or at least fill the confines of the Petri plate?
as the colony expands, it eventually encounters limitations like depleted nutrients, accumulation of waste products, limited space, and competition between individual cells within the colon
Could a pure culture of bacteria be obtained by the streak plate method if there were only one desired microbe in a bacterial suspension of billions?
It is possible but would be better if you used the selective media to kill off unwanted colonies first THEN use streak method to obtain a pure culture.
as long as that single microbe gets sufficiently separated from the others during the streaking process, allowing it to form a distinct colony which can then be isolated to create a pure culture;
Ways to preserve bacterial cultures
- Deep freezing
- Lyophilization (freeze drying)
At what temp does deep-freezing occur?
-50 to -95c
At what temp does Lyophilization occur?
-54 to -72 C
gets frozen then dehydrated
If the Space Station in Earth orbit suddenly ruptured, the humans on board would die instantly from cold and the vacuum of space. Would all the bacteria in the capsule also be killed?
Some bacteria might get lyophilized
What does bacterial division do?
Increase in number of cells, not cell size
Binary fission
asexual reproduction where a single-celled organism divides into two identical daughter cells
What is Budding?
asexual reproduction where a new organism develops from a small outgrowth or “bud” that grows on the body of a parent organism, eventually detaching to become a separate individual
(actinomycetes)
group of microbes that make antibiotic compounds and other important metabolites
Conidiospores (actinomycetes)
asexual reproductive spores produced by fungi
Fragmentation of filaments
organism is split into fragments upon maturation and the spilted part becomes the new individual.
Bacterial cells do not divide by
meiosis and mitosis
Most bacteria grow asexually, by a process known as
binary fission
What happens in binary fission?
- Bacteria copies its chromosome
- elongates and splits making two identical daughter bacteria
Can each daughter cell split?
Yes
Step one of binary fission
cell elongates and DNA is replicated
Step 2 of binary fission
Plasma membrane begins to constrict and a new wall is made
Step 3 of binary fission
cross-wall forms, completely separating the two DNA copies
Step 4 of binary fission
cells separate
How does binary fission multiply the number of cells
doubles the number of cells each generation
Total number of cells made by binary fission. Formula.
2^(n)
n= number of generations
Growth curve of binary fission
logarithmically
Unlike eukaryotic cells, bacteria do not need to do what during replication?
assemble mitotic spindle , binary fission is faster.
Can a complex organism, such as a beetle, divide by binary fission?
no, Its only possible for single celled organisms that reproduce asexually
What are the phases of growth?
- Lag phase
- Log phase
- Stationary phase-Bacteria approach the carrying capacity
- Death phase
What happens during the stationary phase?
Bacteria approach the carrying capacity
carrying capacity
the number of organisms that an ecosystem can sustainably support
- Lag phase
Intense activity preparing for population growth, but no increase in population.
- Log phase
Logarithmic, or exponential increase in population
What causes the logarithmic growth in the log phase?
reproduction by binary fission (bacteria), or mitosis (yeast)
yeast reproduces by
mitosis
bacteria reproduces by
binary fission
Stationary phase
microbial deaths balance production of new cells.
Death phase
population is decreasing at a logarithmic rate
Growth in bacteria is defined as
an increase in the number of bacterial cells within a population.
What do the bacteria do in the lag phase?
adjust metabolic activity to the new medium. The number of new cells is equivalent to the number of dying cells.
lag phase can last from
less than an hour to days depending on species
When is the graph linear?
log of number of cells vs generation.
How do bacterial cells survive without nutrients?
switch metabolism to dormant state
If two mice started a family within a fixed enclosure, with a fixed food supply, would the population curve be the same as a bacterial growth curve?
No, this growth curve applies to bacteria and mammals function differently. Mammals use more resources to produce and the mice would, most likely, use most of there food supply before bacteria would
What do direct measurements do?
count microbial cells
types of direct measurements
Plate count
Filtration
Most probable number (meter P N) method
Direct microscopic count
When do you use plate counts?
Count colonies on plates that have 30 to 300 colonies (C F Us)
How do you ensure the right number of colonies in plate counts?
the original inoculum must be diluted via serial dilution
Plate counts are performed on
bacteria mixed into a dish with agar (pour plate method) or spread on the surface of a plate (spread plate method)
Pour plate method
bacteria mixed into a dish with agar
Spread plate method
Spread on the surface of a plate
What is filtration?
Solution passed through a filter that collects bacteria
Filter is transferred to a Petri dish and grows as
colonies on the surface
What happens in the Most Probable Number MPM Method
Multiple tube test
Count positive tubes
Compare with a statistical table
Function of MPN tables
calculate the microbial numbers that are statistically likely to lead to such a result
Direct microscopic count- How does it happen?
- Volume of a bacterial suspension placed on a slide
- Avg num of bacteria per viewing field is calculated
- uses Petroff-Hausser cell counter
Number of bacteria / ml formula
(# of cells counted) /(volume of area counted) = number of bacteria/ml
Why is it difficult to measure realistically the growth of a filamentous mold isolate by the plate count method?
filamentous fungi tend to form complex, interwoven networks of hyphae that can easily fragment during sample preparation, leading to multiple colonies arising from a single hyphae fragment, thus overestimating the actual number of viable cells present in the original sample. Break off and make more leading to overestimation
Turbidity
measurement of cloudiness with a spectrophotometer
Metabolic activity
amount of metabolic product is proportional to the number of bacteria
Dry weight bacteria are
filtered, dried, and weighed; used for filamentous organisms
Direct methods usually require an incubation time for a colony. Why is this not always feasible for analyzing foods?
food often has a high microbial load, potentially leading to overgrown plates where individual colonies cannot be accurately counted, and the rapid analysis needed for food safety often cannot accommodate the incubation period required for colony growth
If there is no good method for analyzing a product for its vitamin content, what is a feasible method of determining the vitamin content?
Metabolic Method - assumes metabolic product is proportionate to # of bacteria present
(ex. Acid production determines amount of vitamins)
