Mikrobiologi 3
How is growth defined in microbiology according to the course-book? Can growth be defined in other ways?
measured by the increase in population by measuring the increase in cell mass and increace in cell number.
What is binary fission
Cell division following enlargement of a cell twice its minimum size
Generation time
The time required for a population of microbial cells to double
Typical growth curve
It is divided in four phases. 1. Lag phase. 2. Exponential phase. 3. Stationary phase. 4. Death phase
Lag phase
The first phase in a growth curve. Low number of cell division and ATP and growth factors are missing. Ribosomes downregulate, specific enzymes are missing and cells can be damaged. This phase is needed for the bacteria to adjust to the new environment.
Exponential phase
Rapid and constant cell division occurs here. The bacteria divide at a consistent rate through binary fission, this leads to an exponential increase in population.
Stationary phase
Cells stop dividing. Lack of nutreins and oxugen levels are changing. Acid and waste- products are accumulated and pH drops. Here the cell population stabilizes they reach an equilibrium.
Death phase
This is the last phase in the growth curve where the cells die. This occurs when the conditions become unfavorable to support bacterial survival.
What factors are required for bacteria to grow
Access to water, nutrients, oxygen level, pH level and temperature
What are obligate aerobic-, obligate anaerobic-, facultative anaerobic- and aerotolerant bacteria? What does it mean that bacteria are microaerophilic?
Obligate aerobic bacteria grows in the presence of oxygen. Obligate anaerobic bacteria dies in the presence of oxygen. Facultative anaerobic bacteria grow in the presence of oxygen. Aerotolerant bacteria can handle oxyge n but cannot use it in cellular respiration.
Microaerophilic bacteria
Grows in the presence of low oxygen levels and can only low levels in cellular respirtion.
How can you test if a bacteria is obligate aerobic, obligate anaerobic, etc?
You can use a sample tube with a thioglycollate broth
How does temperature affect bacterial growth
If its to cold, the bacteria does not grow. Between 20-50 degrees celsius rapid growth occurs, a litle hotter than that slow repruduction of bacteria occurs and over 70 degrees most bacteria are destroyed.
Psychrophilic bacteria
Grows in low temperature, around -10 to 10 degrees
Mesophilic bacteria
Grow in mid temperature, around 10 to 45 degrees.
Thermophilic
Grow in high temperature around 40 to 70 degrees.
Hyperthermophilic
Grow in very high temperature 65 to 115 degrees
What happens with bacteria when it boils
it vill be destroyed and die. Bacterias like thermophilic and endospore forming bacteria can survive
How does pH affect growth
It affects enzyme activity, membrane stability and overall cellular functions
Hyperosmotic shock
When a bacterial cell is exposed to a hypertonic environment, this lead to water loss and can cause cell shrinkage and death
When plotting total bacterial cell number in a logarithmic scale as a function of time exponential growth and death-phase appears as straight lines. Why?
It is because of exponential decay transforms into a linear equation when taking the logarithm.
What is post-exponential and early stationary phase of growth?
Post-exponential phase occurs immediately after the exponential phase. During this stage the rapid cell division begins to slow. Early stationary phase comes after the post- exponential phase. Here the growth rate stabilizes and it results in a steady- state population
What is continuously culturing?
It is a method of growing microorganism in a controlled system where fresh nutrients are continuously supplied and wate products and excess cells are constantly removed.
Chemostat
The chemostatis an open system used to maintain cell populations in exponential growth for extended periods. The rate which a culture is diluted with fresh growth medium controls the doubling time of the population while the cell density is controlled by the concentration of a growth- limiting nutrient dissolved in fresh medium
what is a steady- state when considering continuous growth?
It is when bacteria is forced to exponential growth for a very long time
What dangerous oxygen species exist=
Superoxide anion O2-. Hydrogen peroxide H2O2.
How does dangerous oxygen form
They are formed when oxygen is reduced into H2O.
How do you control dangerous bacteria
You can control it by catalase, peroxidase, sueroxide, dismutase and superoxide reductase
What are cathalase and oxidase test
You use it to characterize bacteria. It can be used to discriminate enteric bacteria from other gammaproteobacteria
How can you count the total number of bacteria in a sample
Direct methods- using a microscope and the plating technique of Koch. Inderect method- turbidity measurements
What are the limitations when using microscopic counting to estimate the number of bacteria in a solution?
You will need a microscope, small cells can be missed and you are measuring both dead and living cells
what is viable count
It is a measurement of the concentration of live cells in a population. Plate count method is one example of viable counts
Spread- plate VS pour-plate
In a spread plate method a volume of an appropriately diluted culture is spread over the surface of an agar plate spread. In the pour- plate method a known volume of culture is pipetted or poured into a sterile petri plate
Plating technique of KOch
1. One unit of sample is dilutet in 9 units of sterile physiological NaCl- solution. 2. One unit of the dilution is aded to 9 units of NaCl- solution 3. One unit of this dilution is further added to 9 units of NaCl- solution resulting a 100- fold dilution. 4. 100 microliter from each dilution is used to inoculate bacterial growth
Colony- forming unit (CFU)
Measurement of viable colonogenic cell numbers in CFU/mL
Turbidity
A measurement using a spectrometer, an instrument that measures how much light that passes through a cell suspension. The unit for turbidity optical density at the wavelength specified.
OD
Optical density, it is a turbidity measurement of microbial growth.
Why do you sometimes need to dilute a bacterial sample before you measure OD on an OD-meter?
It ensures accuracu, prevents errors from excessive light scattering and keeps reading within the spectrophotometers linear range. You shuld dilute if it measuers 1 or over
Would you expect the growth curves of the same culture to differ if you are measuring turbidity of the culture instead of CFU/ml? If so, why?
Yes OD measures total biomass which is both live and dead cells. CFU/mL only measures viable cells
Decontamination
Treatment of an object surface to make it safe to handle, ex wiping the table after a meal
Disenfection
A chemical of physical agent that directly target pathogens are used ex ytesdesinfection
Sterilization
When you kill and remove all viable organism ex autoclave
Bacterial agent
An agents that kills microorganism
Bacteriostatic agent
An agent that inhibits the growth of the microorganism
Decontamination VS disenfection
A specific chemical agent is used to target and kill pathogens in disenfection. In decontamination only reduces pathogens but does not always kills
Which three parts are included in physical antimicrobial control? How does each work?
Heat sterilization is when you use a very high temperature and macromolecules deature.
Radiation is when you use radiation to alter and disrupt biopolymers such as DNA and protein, there are two types, ionizing with X-ray and gamma ray radiation and you get a sterile product and UV where the number of microorganism are reduced.
Filter is used if its liquids and you use a membrane filter to make a sterile product and if it is gases you use a hepa filter for decontamination
Decimal reduction time (D)
The time required for a 10- fold reduction in the viability of a microbial population
Thermal death time
The time required to kill all cells of a microbial population at a specific temperature
Denaturation
When the weak bond or components get destroyed, the protein will unfold and lose their structure and function. This happens when temperature, pH or salt concentration changes
Problems with endospores and heat sterilization
They are able to survive heat and have a longer decimal reduction time than vegetative cells
Autoclaving process
It is three stages, pretreatment, sterilisation and finishing, Pretreatment, air is pumped out of the chamber and steam is added and pumped out again with air. Sterilisation, it goes through 134 for 3 minutes or 121 for 15 minutes. Finishing, the pressure rapidly droppes and the boiling point of water will be reduced.
Defininition of sterile
Less than 1 bacterium/endospore per 1.000.000 object
What is pasteurization
A way to reduce number of microorganism. It is often used in the foo industry for example milk where you heat it to a specific degree and then it will last longer because you have redused the microorganisms
Radiation sterilization
When radiation is used to sterilize or reduce microorganisms
Filter sterilization
It is for heat sensitive liquids. The pores of the filters are to allow the bacteria to pass, You can use a membrane filter and a hepa filter
Chemical antimicrobial control
A natural or sunthetic chemical that kills or inhibits growth of microorganism. There are cidal and static agents
Bacteriostatic
Inhibits bacterial growth without killing the bacteria.
OD: Plateause, remains steady
Viable cell count: Plateuse, remains steady
Bacteriacidal
Kills the bacteria leading to a decrease in the population
OD: Remains constant
Viable cell count: Decreases
Bacterolytic
Kill bacteria by lysing them, causing the release of cellular contest.
OD: Decrease
Viable cell count: Decrease
Ethanol based disinfectants
It enters the cell and makes the intracellular protein denaturate. If the concentration of ethanol is to high the cell wall can denaturate too quickly and it will prevent alcohol from penetrating further into the cell and the bacteria can survive