microbiology Flashcards
(54 cards)
Classification of bacteria
The physical difference of bacteria relates to their: size, shape, cell wall structure and hence staining charecteristics- genetic difference produces different metabolic features and different surface molecules- so they have different surface properties.
Classification of bacteria- prokaryotes
Prokaryotes vary a lot in size- smallest = archea- the size of the smallest cells is limited by size of molecules needed for life.
staphyloccocus aureus
classification by shape
a genus of a bacteria has 3 main shapes- shape sometimes is indicated in its name Bacillus or rod shaped-Eschericha; bacillus Coccus or spherical- staphyloccocus; streptococcus Spiral or corkskrew- spirillum
Further identification…
According to the way bacteria groups- may be single- helicobacter, in pairrs eg Diplococcus pneumoniae or in chains eg Streptococcus or in clusters eg Staphylococcus
Classiication by gram stain reaction
Gram stain allows people to distinguish between gram positive and gram negative bacteria
Difference between gram positive and gram negative bacteria
The cell wall of all bacteria is a 3 dimensional network of polysaccharides and polypeptides, known as peptidoglycan or murein- cross linking of these molecules provides strength- gives cell its shape- protects against swelling or bursting caused by osmotic uptake of water- +ve has this basic cell wall structure whereas gram negative has an extra layer of lipopolysaccharide
So why does +ve and -ve stain differently
Gram positive bacteria have cell walls with a thicker layer of peptidoglycan/murein (than Gram-negative bacteria), which retains the crystal violet/iodine complex within their cells when washed with alcohol - staining purple.
more on difference between +ve and -ve- staining/ positive
On treatment with alcohol, the Gram negative cell walls lose their outer lipopolysaccharide membrane, and the thin inner peptidoglycan layer is left exposed, this means that the crystal violet/iodine complexes are washed from the gram-negative cell along with the outer membrane - they stain red with the counterstain safranin Absence of outer layer means +ve can bind stain efficiently but does make them more succeptible to penicillin and enzyme lysozyme
more on difference between +ve and -ve- negative
Gram negative’s cell wall is supplemented with large molecules of lipopolysaccharide that protect cell- exclude dyes like crystal violet lipopolysaccharide protects peptidoglycan below- more resistant to penicillin- needs different antibiotics which interfere with cells ability to make proteins - eukaryotic cells also make proteins but protein making machinery is different- unaffected by antibiotics
Lysozome effect
Bacteria constantly makes/ breaks chemical links in cell walls- lysozyme hydrolyses these bonds holding peptidoglycan molecules together
Penicillin effect
Prevents bonds interlinking peptidoglycan molecules from forming- significant when bacteria make new cell walls when they divide- makes the cell walls weak and easy to collapse- water uptake by osmosis bursts the cell
gram staining
Image: Gram Staining (binary/octet-stream)
gram positive vs negative structure
Image: Gram Positive Vs Negative (binary/octet-stream)
chemicals used in gram staining steps
Crystal violet- basic dye- binds to peptidoglycans so all bacteria stain purple Lugol’s iodine- Mordant- Binds crystalviolet to peptidoglycan more strongly Acetone alcohol- Decolouriser- removes unbound crystal violet and lipopolysaccharide- -ve loses stain goes colourless, +ve stays purple Sutamin- counter stain- -ve- red, +ve- stays purple
Conditions necessary for culturing bacteria in lab
Bacteria reproduce asexually by binary fission and can be cultured on a nutrient rich agar jelly or in a nutrient broth. These growth media must include: ● A suitable carbon source, usually glucose or lactose ● A suitable nitrogen source such as ammonium or amino acids ● A source of sulphur and phosphorous ● Vitamins, minerals and growth factors ● A suitable pH ● The growth media should be incubated at a suitable temperature – 25oC ● Different species vary in their requirements and usually grow over a range of temperature and pH values, with an optimum within the range
nutrients
glucose/ lactose- glucose= easier to break down- monomer- carbon- needed for making up organisms eg proteins, lipids, carbohydrates- carbon mostly provided in organic form (glucose not CO2- bacteria adapted to living on organic (living or once living material)
Nutrients pt 2
nitrogen needed for proteins, DNA, RNA- usually given in organic form (proteins) or inorganic form (nitrogen gas or ammonia) growth factors- essential substances that the bacteria can’t synthesize itself from simpler substances- needed in tiny amounts- vitamins to make enzymes, mineral salts, amino acids
The effect of oxygen
●Obligate aerobe require oxygen for metabolism ●Obligate anaerobe metabolism is inhibited in the presence of oxygen. ●Facultative anaerobes grow best in the presence of oxygen, but can respire anaerobically if they need to
How to classify bacteria- oxygen
Obligate aerobes- bacteria are clustered at top of tube as they need oxygen for respiration and growth (O2 diffuses from air into growth medium) Obligate anaerobes- bacteria are at bottom of tube, away from their source of oxygen Facultative anaerobes- bacteria is found throughout tube but mainly toward top can grow without O2 but grow best with it
Aseptic techniques are used to prevent…
Contamination of the environment by the microorganisms being handled. Contamination of the bacterial cultures by unwanted microorganisms from the environment
