Flashcards in Microbiology Deck (51):
What are the 3 domains of life?
What morphological features could you distinguish microbes using?
Cell shape and size
Villa and flagella
What physiological and metabolic characteristics can microbes be distinguished under
Carbon and nitrogen sources
Cell wall constituents
General nutritional requirements
Growth temperature optimum
Water activity requirements
Salt requirements and tolerance
What’s the hierarchy or taxonomy?
Domain - bacteria
Phylum - protobacteria
Class - alpha beta protobacteria
Family - enterobacteriacae
Genus - escherchia
Species - coli
What temperatures do psychropjile, mesophile, thermophile, psychotroph and hyperthermophiles like?
Psychrophile - below 20
Mesophile - between 20-50
Thermophile - above 50
Psychotroph - between 20-50 but low
Hyperthermophile - above 80
What are he % oxygen requirements for aerobes, anaerobes, microaerophiles and facultive organisms?
Anaerobes - 0%
Microaerophiles - 2%-10%
Facultive organisms - 0-21%
What are the 2 microbial growth requirements with examples?
Macronutrients - C,N,Pho, S, K
Micronutrients - Fe,Ca,Mg,Mn,Zn
Growth factors - vitamins, amino acids, nitrogenous bases
What is an undefined(complete/complex) medium?
An undefined medium has some complex ingredients, such as yeast extract or casein hydrolysate, which consist of a mixture of many chemical species in unknown proportions. Yeast extract, beef extract etc.
What is a defined medium?
A chemically defined medium is a growth medium suitable for the in vitro cell culture of human or animal cells in which all of the chemical components are known.
What is the difference between prototrophs and autotrophs?
Autotrophs - mutant organism especially bacterium that requires particular additional nutrient which the normal strain does not?
Prototroph - a microorganism that has the same nutritional requirements as a parent organism. Capable or synthesising its metabolites from inorganic material requiring no organic nutrients
What is enriched medium?
Enriched with extra supplements, such as horse blood agar and chocolate agar
What is a differential medium?
A medium that allowing the differentiation of two species. Regarding the growth of one and allowing the growth of the other
What are the three types of cells that can be counted?
Viable but not cultivable - low metabolic activity and do not divide
What two instruments are usually used for cell counting?
How does a haemocytometer work and what are its advantages and disadvantages?
Cells counted on a special microscope slide with a grid to allow counting of cells
- can distinguish between inanimate matter and cells
- long process
Subject to human error
-average cell count)x(1/volume in sample cm3)x(1/dilution factor)
What is a coulter counter and how does it work?
Cells pass through different sized orifice in a glass tube and are measured electronically. Cell size and number can be determined.
-Automated and rapid
-not subject to human error
-requires expensive equipment
-can not distinguish between cells and inanimate matter or distinguish species
-average cell count)x(1/volume in sample cm3)x(1/dilution factor)
What 3 methods are used for determination of variable count?
Spread plate on solid medium
Pour plate on solid medium
Most probable number in liquid medium
How is the spread plate method carried out?
-sample of known volume and solution pipettes onto surface and spread with sterile spreader
How is the pour plate method carried out?
-sample of known volume and dilution pipetted into empty sterile plate
-sterile medium is added and mixed well with the same ole
-plate is incubated at suitable temperature
-the number of colonies on the plate are counted
What is the equitation for spread plate and pour plate methods?
=average colony count (1/dilution factor)x(1/sample volume)
What is the most probable number method of counting cells and what advantages does it have?
Probability of viable cells present in diluted sample follows Poisson distribution.
Essentially making serial dilutions and checking for growth in each
(Organisms/volume of dilution)x(1/most concentrated dilution) = number of cells
-Can be used for species that do not readily form colonies on solid medium
What methods of dry weight determination are there and how do they work?
Small particles scatter light in proportion to their concentrations. This can be measured as absorb acne and a day weight can be calculated using a graph.
Dry weight determination
Record weight of centrifuge tube - A
Add known volume of liquid culture
Harvest cells by centrifugation
Record weight of wet cell pellet in tube B
Dry cel pellet at >100 degrees to constant weight
Record weight of dry cell pellet in tube
What is required in a continuous culture for it to function?
Substrate to be a limiting factor to allow medium to remain at exponential phase
Overflow system for volume to remain constant
What is cell generation time or (td)?
Td is the cell generation time, it is usually around 0.693t
What is cell yield?
Amount of growth produced usually as dry weight per unit amount of substrate produced. Both weights have to be in the same unit
What is a synchonomous culture and how is it obtained?
All the cells are at the same stage of the cell cycle
By applying an environmental shock such as heat shock.
Or selecting cells of the same size
By repeated lowering asynchronomous cell cultures to a sub optimal level then repeating over time
By size filtration
Where does the growth/germ tube grow?
Apically forming a hypha which grows exponentially. The branches are produced on alternating sides.
Produced by apical succession, the youngest branch is closest to the apex.
What is a mycelium? And how are they formed?
A network of branches hyphae. Vesicles with lytic enzymes bind to the cell wall weakening them. Enzymes include chitinase. Chitin synthase
And glucan synthase are then used to repair the wall.
How are the hypha elongated?
Water and nutrients move up the hypha forming turgor pressure that forces the tip to extend. The hypha stay away from each other though negative tropism, they are attracted to areas with more nutrients causing them to stay away from each other
What is hypha growth unit?
A way of calculating the growth of hypha, calculated as
G=total length of mycelium/ no of branches
The value is unique to each fungi
What is chemotaxis and what are the stimuli?
The movement of bacteria towards or away from a stimulus. Attractants and repellants
What is the difference between clockwise and anti-clockwise rotation of the flagella?
Clockwise is random movement known as tumbling
Anti-clockwise is deliberate movement
Name the parts of the flagellum?
3 main parts
-complex body with various components
- a complex nasal body with a P ring, M ring, L ring
(m ring insisting of FliG and Mot A and B proteins)
Not A and B are channel proteins within the cytoplasm
How does the flagella change rotation?
FliG receives signals from methl accepting chemotaxis proteins (MCPs)
What are the methods of nutrient uptake against a concentration gradient?
ATP Binding Cassette (ABC) transport
What methods do antibiotics work by?
Interference with cell wall synthesis
Inhibit protein synthesis
Interfere with nucleic acid synthesis
Inhibit metabolic pathways unique to bacteria
Disrupts bacterial membranes
What is a high chemotherapeutic (C.I) index?
A high maximum tolerated dose compared to a low minimum curative dose
Maximum tolerated dose/minimum curative
What is the antibiotic sensitivity test?
Paper discs containing known concentrations of antibiotics are placed on a freshly prepared spread plate. Some of inhibition examined.
What is meant by minimum inhibitory concentration?
The minimum bacterial concentration is the lowest concentration of antibiotic that inhibits growth.
What’s the difference between disinfectants and antiseptics and how to they work?
Reduce viable microbial population to a threshold level. However antiseptics can be used on living tissue.
What factors effect efficacy of a disinfectant?
Large volume of disinfectant
Lower microbial loud
Presence of inactivating compounds
What modes of action do alcohols, glutaldehyes, halogens, iodine, phenol employ to act as disinfectants?
Alcohol - denature proteins
Glutaldehyes - cross link proteins + nucleic acids
Halogens - yield chlorinated based
Iodine - interacts with nucleotides, fatty acids and amino acids
Phenol - denatures proteins
What is sterilisation and disinfection? What methods of sterilisation are there?
Sterilisation - freeing an object of all living bacteria spores, fungi and viruses
Heat, filtration, radiation
Disinfection - elimination of all pathogens but not all microorganisms
What types of pasteurisation are there?
Holder - 63oC for 30 mins
Flash - 72oC for 15-20 seconds
What are boiling, low temperature steam and filtration?
Boiling - object in boiling water for 5 minutes
Low temp steam - sub atmospheric pressure generate steam at low temps. 75oC for 20-30 mins
Filtration - high efficiency particulate air
Captures 99.97% bacteria in air. Used in laminar flow safety, operating rooms and isolation rooms for inmunocompromised individuals
What is thermal death point, thermal death time and decimal reduction time?
Thermal death point - lowest temperature used to kill microorganisms within 10 mins in an aqueous environment
Thermal death time - time taken to achieve complete killing of microorganism at given temperature
Decimal reduction time - the time taken to reduce the microbial population by 90% at a stated temperature
What is constitutive control of enzyme production?
Enzyme production occurring under all conditions eg those needed for glycolysis
What are the 4 types of control of enzyme transcription?
Induction - controlled by concentrations of enzymes
Repression - controlled by concentrations of enzymes
Autogenous - transcription occurs anyway but the concentration of eg free ribosomes affects transcription. No accumulation of free ribosomes causes transcription to occur, once built up the free ribosomes binds the 5’ of mRNA.
Explain simple feedback inhibition, branches inhibition, triple branched?
Simple inhibition forms one product and the product interferes with its own synthesis
Branched has 2 products which can respectively affect their own synthesis
Triple branched has 3 products which can also respectively affect their own synthesis
What is the effect of transcription on an operon when catabolic activity is high? And when it’s low?
High catabolic activity leads to low cAMP disallowing transcription
Low catabolic activity leads to high cAMP allowing transcription