Chapter 6 Microbial Growth Flashcards
What is the definition of microbial growth?
It the increase in the number of cells not the cell size.
What do cells grow into?
Cells grow into a colony
What can understanding microbial growth do for us?
If we understand the conditions that are necessary for microbial growth, we can prevent disease and food spoilage.
What are the physical requirements for growth?
Temp
-pH
Osmotic
What are the chemical requirements for optimal microbial growth?
Carbon Nitrogen, sulfur, and phosphorous Trace elements Oxygen Organic growth factor
How is temperature described in microbial growth?
Minimum growth temp
Optimal growth temp
Maximum growth temp
What are Psychrophiles/Psychrotrophs? What are their temperature ranges and what are they responsible for.?
Cold-loving
They grow in the refrigerator
Cause food spoilage
Psychrophiles grow below 20 C
Psychrotrophs- grow 0-30 degrees C
Describe Mesophiles optimal growth temp?
Moderate temp-loving
Because body temp is 37 C, pathogens belong to this group
Describe Thermophiles and their optimal growth temp?
They grow above temps 40 C and will not grow below 40 C.
Below 40 are called obligate thermophiles
What is the range of optimal grow for most bacterial in regards to food preservation?
What temp do many bacteria survive, and some may produce toxins
20-50 for rapid growth of microbes in food
5-15 C bacteria survive and many produce toxins
What are refrigerator temps and what takes place with growth?
0-15 C refrigerator temps which may allow slow growth of spoilage bacteria by very few pathogens
What happens to bacteria at temps within a freezer?
Under zero, no significant growth below freezing
What pH do most bacteria grow in?
6.5 to 7.5
What is the optimal pH that molds and yeasts grow in?
-pH 5 and 6
What pH is effective to keep bacteria from growing? What is a process that uses this pH?
Very few grow below pH 4. This pH is what is used to make yogurt, pickles, sauerkraut. And this prevents spoilage
What type of environment causes bacterial to lose water? And what takes place?
Hypertonic environments, or increase in salt or sugar will cause plasmolysis
The cell will lose water and the plasma membrane pulls away from the cell wall and causes death
This is bacterial osmotic pressure
What bacterial survive in areas that have high salt and have high osmotic pressure?
Who can tolerate these environments as well.
Extreme or obligate halophiles (salt loving) require high osmotic pressure
Facultative halophiles tolerate high osmotic pressure
How can bacteria tolerate Hypotonic (pure water)?
Because the plasma membrane rest on the rigid cell wall and prevents damage
What are the chemical requirements for bacterial growth?
Need a carbon source and an energy source
What the energy sources that are used for bacterial growth?
What do chemoheterotrophs and autotrophs use?
Energy source comes from carbohydrates, proteins and lipids.
Chemoheterotrophs use organic carbon sources
Autotrophs use CO2
What is another chemical requirements that comes from amino acid and proteins?
Nitrogen - comes from amino acids and proteins
Most bacteria decompose protein
What can N2 gas be used for and what bacteria uses it and for what?
N2 is use for nitrogen fixation
Rhizobium (symbiosis with plant roots)
Besides Nitrogen what other elements are used by bacteria for growth?
Sulfur and Phosphorus
What sulfur and phosphorus compounds are used?
Where are these compounds found?
Sulfur is present in come AA
Phosphorus is in DNA, RNA, and ATP and membranes
Some bacterial use SO4 2- (sulfate) or H2S (rotten egg gas)
PO4 3- is a phosphate ion and a source of phosphorus
What are trace elements?
These are inorganic elements that are required in small amounts to help enzymes function.
Fe (iron), Cu (copper), Zn (Zinc) these are enzyme cofactors
What is the effect of 02 on growth?
Even though we need it O2, its a poisonous gas
What type of bacteria need O2 to grow?
Obligate aerobes need O2 to grow
What bacteria can grow in the presence of O2 but can live without it?
What type of environment causes this growth without O2 present
Facultative anaerobes: use O2 when present but can live without it.
Without its fermentation or anaerobic respiration. E. coli
What type of bacteria lives without the presence of O2?
Obligate anaerobes: can only live in the absence of O2
O2 is toxic to these bacteria because they don’t have SOD and Catalase enzymes.
SOD breaks down superoxide radicals to O2 and peroxide. Catalase breaks down peroxide to water and oxygen
What is an example of an obliged anaerobes?
Clostridium which cause tetanus and botulism
What are Aerotolerant anaerobes?
Do not need O2 but can tolerate it
What microbes use O2 but need less of it to survive.
Microaerophiles: they are aerobic but need less concentration of O2 because they produce a large amount of toxic material in the presence of O2.
What are the forms of toxic oxygen?
Singlet oxygen: these are vey reactive and found in phagocytic cells
Superoxide free radicals (O2-) is very toxic found in obligate anaerobes
What enzyme neutralizes superoxide free radicals
SOD Superoxide dismutase
What enzyme neutralizes peroxide anion and generates O2, which one does not produce O2?
Catalase produces O2
Peroxidase does not generate O2
What is the most reactive molecule, this is also one of the body’s best defenses agains pathogens?
Hydroxyl radical
Very reactive molecule
Where are Organic growth factors found?
What is a key feature about them and our body?
Organic compounds obtained from the environment
They are vitamins, amino acids, purines, and Pyrimidines
These are essential and found in our environment. We are unable to synthesize them.
Bacteria seldom live individually. Where do you find bacteria? What type of community?
Microorganisms live in communities called Biofilms
What are Biofilms?
They are a thin slimy layer that encase bacteria, which allow them to adhere to surfaces easier
What are Biofilms composed of, and what do they form?
Made of polysaccharides and they form slime or hydrogels
they are found on the surface of a rock or the human tooth
What is distinct trait about a biofilm community?
Their function within the community are usually coordinated together. They are able to coordinate their activity as a group
How do bacteria within a biofilm communicate?
Use cell-to-cell communication called Quorum sensing
What are the benefits of a biofilm?
They can share nutrients
They are sheltered from harmful factors like desiccation and antibiotics
Also allows for the share of genetic information through conjugation
What problems do Biofilms cause humans?
They are a factor in human disease
They cause nosocomial infections that are acquired in hospitals: like on a catheters
What is lactoferrin? What does it do?
Found in human secretions (milk) and inhibits biofilm formation
What was found on the catheters in hospitals after it was grown for several days?
Pseudomonas fluorescens was cultured form the catheters
What is culture medium?
Nutrients prepared for microbial growth
What does sterile mean?
No living microbes
What is the difference between inoculated and contamination?
Inoculum: Intentionally introducing microbes into a medium
Contamination: undesirable bacterial presence
What is a culture?
It’s the microbes that grow in or on a culture medium
What is Agar?
What is it made of?
It’s a complex polysaccharide that is used as a solidifying agent for culture media in Petri plates, slants and deeps
Not metabolized by microbes
Why is agar being used and what was originally use and why did we stop using it?
Used to use gelatin, but some bacteria could utilize it
What are its working temps?
Agars liquid temp is: 100 C
It Solidifies at ~40 C
What is chemically defined media and complex media?
Chemically defined media: exact chemical composition is known
Complex media: extracts and digest of yeasts, meat, or plants
What are examples of Complex media?
Nutrient Broth
Nutrient Agar
What type of media does Anaerobic microbes need?
Reducing media
What types of culture methods does anaerobic microbes need to grow?
Reducing media
What is reducing media?
Contains chemicals like thioglycolate or oxyrase that combine to with dissolved O2 to deplete it
They are then heated to drive off the O2
What are some things used to remove O2
Anaerobic Jar, Anaerobic Chamber, and capnophiles.
What are Capnophiles?
Microbes that require high CO2 conditions
These conditions can come from CO2 packets or a candle jar
What is selective media?
This media suppress unwanted microbes and encourage desired microbes
What is Differential Media?
Bacterial colonies that show distinctive appearance on different media
A way to distinguish specific organism based on the media being used.
Ex MSA S.aureus like the high salt environment
Makes it easy to distinguish colonies of different microbes
What is Enrichment Culture used for?
Encourages growth of desired microbe that is in small numbers. This will help produce enough of the bacteria to form a colony
This is often used on soil and fecal samples.
What is colony? Which comes from what?
A colony is a population of cells arising from a single cell or spore or from a group of attached cells.
A pure culture contains only one species or strain
What is the method used to isolate pure cultures?
The streak plate method
What are two other methods used for isolation of a pure culture?
Pour Plate and spread plate method
How do prokaryotes reproduce? What are the different methods?
Divide by binary fission, budding, and some by Conidiospores, some by fragmentation of filaments
What are the steps of Binary Fission?
Cell elongates and DNA is replicated.
Cell wall and plasma membrane begin to constrict
Cross-wall forms, completely separating the two DNA copies
Cells separate
What does the number that is the exponent or power of 2 show in bacterial generation?
When the number of cells is expresses as a power of 2, then the exponent show the number of generation
2^0 = 1 initial number of cells 2^1 = 2 number of cells after the first generation 2^2 = 4 number of cells after 2 generations 2^3 = 8 number of cells after 3 generations
What is doubling time?
The time required for bacterial cells to divide or double in number
Using standard numbers to define the total number of bacterial that has divided is way to big. What is used in its place?
Use a logarithmic scale
What is the difference between logarithmic and arithmetic graphs when graphing cellular growth?
Arithmetic plot Dow not shoe the population changes in the early stage of growth
When the growth began to show it would run off the page.
You are able to graph a best fit line using a logarithmic scale.
What are the 4 phases of Bacterial Growth?
Lag Phase
Log (exponential) phase
Stationary phase
Death phase
Explain the Lag phase. What takes place?
There are no visible changes in the number of cells. The is a period of adaptation
This is the period of preparation for growth but no growth
What is the log (exponential) phase
The sharp increase in the number of cells. It’s a straight line. The generation time is constant.
The cells begin to divide. Reproduction is the most active in this phase
What is the stationary phase?
Growth starts to slow does
The number of microbial deaths balances the number of new cells formed.
What is one of the reasoned cell deaths balances the number of new cells in the Stationary phase?
What is another name for the Stationary phase?
The is due to the exhaustion of nutrients, accumulation of toxic wastes and changes in pH.
This can be referred to as a period of equilibrium.
What is the Death phase?
Number of deaths exceeds the number of new cells ( also called the logarithmic decline phase)
How can we measure growth? Meaning what is measured?
What are the counts that are used to make this measurement?
We can measure the
Cell number and the population total mass
It’s measured either by Viable count: which is the total number of living cells, or by non-viable: which is total cells, either dead or alive.
What are the methods users to measure viable counts and which one is more accurate?
The pour plate method and the spread plate method.
Spread plate method is better to use.
Also use serial dilutions
Why can’t you plate from the first mixture? Meaning no serial dilutions?
Because when plating it there would be a lawn of growth. You are unable to accurately count them.
What is the range to be able to count bacteria?
You want to count colonies on a plate that have 25-250 CFU’s
Some microbiologist say 30-300 CFU’s
When is counting bacteria by membrane filtration used?
Used when the number of bacteria is low and when working with water from lakes and rivers. The filter catches the bacteria.
What are the drawbacks to using the pour plate method?
The agar is at a high temp and some bacteria are unable to handle the 100 C and therefore die. Also the bacteria that form in the Agar could also cause a problem.
What is use when bacteria won’t grow on or in solid media?
MPN. Most probable number
This is statistical estimate. Nothing more than a statement of how many bacteria is estimated to fall within a certain number.
What bacteria is MPN primarily used with?
Most useful to detect coliform (enteric) bacteria that ferment lactose in differential media
It is used in water testing. Lakes and rivers.
When is Direct Microscopic Count done?
Example is when counting bacteria in milk. Time is an issue and must be done quickly, therefore this method is done.
A sample is spread over a slide that is designed to have the area graphed out in the viewing area so that one can count the number of bacteria in them.
What are some disadvantages to Direct count method?
What is an advantage of this method?
Motile cells are hard to count.
Dead cells are counted as live ones giving false results.
Advantage is that no incubation time is needed.
What are the direct methods to measuring microbial growth?
Plate counts
Filtration
MPN
Direct microscopic count
What are the indirect methods for measuring microbial growth?
Turbidity
Metabolic activity
Dry weight: for filamentous organisms
What is turbidity and how is it used to measure microbial counts?
You use a spectrophotometer to measure the turbidity or microbial growth in a sample.
As the number of bacteria grow an increase in turbidity will take place.
As this number of bacteria changes the percent transmission will change indicating a higher count.
You then use absorbance to plot the amount of bacteria
