Classification and Identification Flashcards
What are the types of microorganisms?
What form do they exist in?
Which have cell walls?
bacteria, algae, yeast, moulds, protozoa
virus - generally not included as they re ‘not-living’
can exist as
unicellular, multicellular or cell clusters
cell walls in
bacteria, algae, yeast, moulds - cell walls can be identified using gram stain method
What is the difference between gram positive and gram negative bacteria?
gram positive
- have thick peptidoglycan cell wall = several layers
- plasma membrane = cytoplasmic membrane
gram negative
- outer membrane = lipopolysaccharide and proteins
- lipoproteins
- periplasmic membrane = between inner and outer membrane
- thin peptidoglycan cell wall
- plasma membrane = cytoplasmic membrane
What is the method for gram staining?
1 - flood the smear with crystal methyl violet = primary stain
2 - flood with iodine = forms complex with crystal violet
3 - decolourise with 95% ethyl alcohol or acetone = dehydrates peptidoglycan, destains and allows differentiation between gram + and - = decolourising agent
5 - flood with safranin = counter stain
gram positive - retains crystal violet purple stain due to thick cell wall
gram negative - retains pink/red safranin stain due to crystal violet stain being removed
How do genetic probes identify bacteria?
used to identify species specific DNA and RNA sequences
used to locate specific genes
- have a base sequence complementary to the base sequence of the target allele
- labelled with a compound to identify where it goes
compounds
- fluorescence dye
- peroxidase
What is the difference between macroscopic and microscopic identification?
macroscopic - appearance of colony size, shape, colour - pigment = colour - speed of growth morphology - form - shape, texture - elevation - flat, raised
microscopic
- cell shape and size = cocci, bacillus, spiral, vibrio
- gram stain
- acid fast reaction
- endospore? capsule? granule?
What are the types of bacterial identification?
colony morphology or gram stain biochemical test - oxidase, catalase, urease, coagulase acid fast stain spores growth character - oxygen, temperature, pH motility antigenic properties - molecular or genetic characteristics
How can bacteria be cultured? What are they cultured in?
inoculum is introduced to a medium
inoculum - sample, medium - collection of nutrients
microorganisms that are grown from an inoculum are called a culture
culture can be grown in
broth - liquid
agar - solid
What should a culture media contain?
source of protein
pH control
defined salt concentration
What are the types of agar and what do they contain?
agar
- is a complex polysaccharide derived from the cell walls of red algae
- most microbes cannot digest agar
nutrient agar
- peptone, beef extract, NaCl, agar
tryptone soya agar
- casein enzymichydrolysate, papaicdigest of soyabeanmeal, NaCl, methylumbelliferyl-β-D-glucuronideand agar
What is a progenitor?
may be either a single cell or a group of related cells
is termed a colony forming unit
- colony is an aggregate of cells derived from a single progenitor cell
What are the types of culture media?
defined media
- exact chemical composition is known, synthetic
complex media
- contains nutrients that are released by the partial digestion of beef, yeast and soy
- variety of growth factors means it supports a wider range of microbes = used to grow organisms whose exact nutritional needs are not known
selective media
- contains substances that either favour the growth of a specific microbe or inhibit the growth of unwanted microbes
differential media
- used to distinguish one microbe from another = grow microbes on the same media
- uses biochemical interactions of microbes growing in the presence of specific nutrients/indictors = positive or negative results
anaerobic media
- used to grow anaerobic/facultative microbes
- contain components that chemically combine with and remove oxygen from the media
transport media
- used to move specimen from one location to another
media can be selective and differential
How are microscopes used to identify bacteria?
wavelength of radiation
- radiation differs in wavelength
- electrons move as waves
magnification
- increases size of the objects
- occurs when the beam of radiation refracts as it passes through a lens
resolution
- ability to distinguish two objects that are close together
contrast
- refers to differences in intensity between two objects or between an object and its background
- important in determining resolution
How does electron microscopy work? What are the different types?
must work in a vacuum
uses electrons of wavelengths between 0.01 nm – 0.001 nm = makes resolving and magnification power stronger
types
- transmission electron microscopes = specimen must be thin
- scanning electrons microscopes
How does light microscopy work?
uses light = visible, UV
uses a series of lens for magnification
oil immersion increases resolution and magnification
- add oil to the area being observed
How does staining allow identification? What are the types of stain?
must microbes are colourless
staining increases contrast and resolution
- necessary for light and electron microscopy
simple stain
- composed of basic dye
- involves only soaking the sample then washing off
differential stain
- uses more than one dye
