Separation Of Two Bacterial Species Biology Essay

In the first session, you attempted dividing S. aureus and E.coli bacteriums from a assorted civilization. Analyze your home base after incubation at 37C. for the production of bunchs of growing ( colony organizing units, c.f.u.

s, ‘colonies ‘ or ‘clones ‘ ) on the home bases. Is there grounds of two different bacterial species on the home base? Observe settlement morphology and coloring material for each of the two bacteriums present in the assorted civilization and finish the tabular array below:

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Table I. Separation of S. aureus & A ; E. coli from a assorted civilization



Colony morphology

1Round, white, big settlements, smooth and raised2Punctifom, yellow, little settlements, smooth and raised


What is a bacterial settlement and why it is referred to as a colony-forming unit ( C.F.U.

) ?

A bacterial settlement is a seeable assemblage of beings turning on the surface of or within a solid medium. It is referred to a CFU, as it is comprised of over a million single bacteriums, all posterities from a individual bacteria.


In the old session, you have plated Staphylococcus aureus and Alcaligenes faecalis on both alimentary agar home bases and on home bases incorporating alimentary agar supplemented with 3M NaCl.Observe and contrast the features of any growing on the home bases in the tabular array below:

TABLE II. Growth choice of S. aureus and A.

faecalis by NaCl

Bacterial species

Growth ( +/- )

NA NA + NaCl

S. aureus


Slight growing





Notes: S.

aureus, yellow, Punctifom and smooth

A.faecalis white/colourless, Punctifom.


You inoculated E.

coli and P. vulgaris on McConkey agar. Compare the growing features of both species and enter your observations in the tabular array below:

TABLE III. Differentiation of E. coli and P. vulgaris on McConkey agar

Bacterial species

Colony coloring material

NA McComkey


Notes: McConkey has a pH index which changes coloring material with pH.

E.coli usage lactose which forms lactic acid and changes the pH, the settlements were round, big, smooth and raised

P.vulgaris produces NH4 and changes the pH in the McComkey agar and the index changes coloring materials.

How does the McConkey medium work to distinguish between lactose fermenting bacteriums and those that do non?

This medium is an index medium and a low selective medium. It contains bile salts and crystal violet dye, which hinder Gram-positive bacteriums, impersonal ruddy dye which stains bugs fermenting milk sugar, lactose and peptone.

Lactose fermenting bacteriums such as E.

coli produce ruddy settlements. E.coli used lactose and signifiers lactic acid as a by-product, as the lactic acid has a low pH this lowers the pH of the agar medium and alterations colour due to the index nowadays.Non-lactose zymosis settlements for case salmonella utilise peptone, this signifiers ammonia and increases the pH of the agar hence leads to the formation of white/colourless settlements.

Contrast selective and differential media.

Selective media are intended to cultivate specific bacteriums but non others. It selects for a certain characteristic leting bacteriums to turn for illustration, Mannitol Salt Agar ( MSA ) selects for the growing of halotolerant bacteriums.

The medium has a high salt. Therefore merely bacteriums that can turn in a high degree of salt can turn and remain alive, for illustration S.aureus.

Differential media is designed to show the difference between different beings grown on it for illustration on McConkeys agar some beings look pink while others look colourless

C GRAM Staining

Pure home base civilizations of S. aureus and E. coli were provided to your group to stain utilizing the Gram staining technique that should sort these bacteriums as Gram positive or Gram negative.Detect your Gram stained bacterial vilifications in the microscope utilizing the submergence oil lens taking great attention non to damage the microscope. Read the Appendix and inquire advice from your Coach on how to utilize the oil submergence lens. After usage, carefully wipe oil submergence lens nonsubjective with lint free paper.Record bacteria coloring material ( pink-red or violet violet ) and microscopic form ( cocci or B ) for each of your Gram stained vilifications


Separation of S. aureus & A ; E. coli from a assorted civilization



Bacterial species

Gram staining

Bacteria coloring material Microscopic form

1S.AureusPurpleGram positiveCoccus7E.coliTapGram negativeBacillus


What is the cellular footing for the Gram staining technique? Illustrate your reply with a diagram.

The bacterium that is gram positive has a cell wall that is heavy 20-80 nanometer midst, this is 60-90 % peptidoglycan. It has frequent complecting beds of peptidoglycan.

Besides in the cell wall are teichoic acids, which go throughout the cell wall and are comprised of phosphates, sugar intoxicant ribitol and polymers of glycerin. A few have a lipid attached. The external surface of the peptidoglycan has proteins, which vary with species of the bacteriums. Whereas gram negative cell walls merely contain 10-20 % peptidoglycan and is surrounded by a outer membrane,

In Gram-positive bacteriums the crystal violet and iodine combine to organize a big molecule that precipitates off from the cell. The intoxicant mixture causes desiccation of the peptidoglycan accordingly diminishing the infinite between the cell wall to ensnare the crystal violet complex inside the cell. Whereas in Gram-negative bacteriums the intoxicant mixture dissolves the lipid outer membrane of the cell wall and amendss the membrane on which the peptidoglycan in affiliated and the cell is decolourised.




You used and/or observed a figure of stained bacterial vilifications during Practical 1 and were advised to happen out about the taxonomy, biological science and importance of each of the micro-organisms observed.Use the Table below to enter the most of import characteristics of bacteriums species observed.

TABLE V. Importance of bacterium species observed utilizing compound microscope

Escherichia coli

Bacillus, gm -ve

Synthesizes vitamin K for the liver

Staphylococcus aureus

Cocci, gm +ve

Found in nose and on tegument, capable of bring forthing staphyloxanthin

Alcaligenes faecalis

Bacillus, gm -ve strand

Converts most infective signifiers of arsenic and arsenite to a less unsafe signifier, it is found in dirt and H2O, besides in respiratory piece of lands of people with cystic fibrosis.

Proteus vulgaris

Bacillus, gm -ve,

Ferment sugars in anaerobiotic conditions. Degrades urea to ammonia. Inhabits the enteric piece of lands of worlds and animate beings.

Salmonella typhi

Cocci, gm -ve, flagellated. Pathogen of Typhoid febrility. Found in worlds poulets and cowss

Vibrio sp

Bacillus, gram-ve

Produces antibacterial substances,

Rhizobium leguminosamus

Cocci, blue/green

Fix N in root nodules of leguminous plants. Found in dirt.

Bacillus megaterium

Bacillus, gm -ve, compact

Found in dirt, found in ironss where the cells are joined together by polyoses on the cell walls. Can last utmost conditions conditions. Produces penicillin amidase, which is needed for doing penicillin. It produces enzymes for modifying corticoids.

Nostoc sp.

Bacillus, viridity stranded


Found in salt-cured Waterss, photosynthetic.

Oscillatoria sp.

Bacillus, green stranded.

Filamentous Cynobacteria. Reproduces by atomization. Photosynthetic.


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