Tuesday, January 6, 2009

agar plates

A comparison between Blood agar plate and MacConkeys agar

MacConkeys agar is more tranperent as compaired to the blood agar hence the finger placed below the agar plate of MacConkeys medium is visible and that one below the blood agar plate is not.
Blood agar plate inoculated with Staphylococcus aureus

The Staphylococci are gram positive cocci which live in cluster as the cocci divide in 3 planes and the daughter cocci fail to separate from each other.
On blood agar they form characteristic colonies which shows haemolysis with golden yellow pigmentation in the medium.The pigments are secreted best at 22 degree Celsius.
MacConkeys agar plate showing colonies of Klebsiella species
The colonies produced are large mucoid,dome shaped,lactose fermenting pink colonies.
MacConkeys agar showing colonies of Escherichia coli
The e.coli colonies are circular,2-3 mm n diameter,flat pink due to lactose fermentation with central umbonation.

Pseudomonas aeruginosa colonies on nutrient agar

The colonies are smooth,translucent large low convex 2-4 mm in diameter with irregular spreading edge and sweetish aromatic odour.Fluorescent greenish blue growth and pigment diffuses into medium.

MacConkey's agar plate showing growth of Salmonella typhi

The Salmonella typhi colonies are circular low convex smooth translucent,colourless due to absence of lactose fermentation.

Salmonella species are the causative agents for Typhoid fever.
Blood agar plate showing growth of Proteus species

The organism shows characteristic swarming in the form of succesive waves forming concentric circles with fishy smell.The swarming can be prevented by increasing the concentration of agar to 6% as compared to normal which is 2%

The important organisms in proteus species are Proteus vulgaris and Proteus mirabilis

Blood agar plate showing colonies of Vibrio cholerae

Most of the colonies are surrounded by zone of greening which later clear due to haemodigation.

This organism is responsible for cholara disease.

TCBS agar plate-Uninoculated

Thiosulphate citrate bile salt sucrose medium.

This medium is selective as well as differential medium for vebrio cholara.

It contains yeast extract,peptone,sodium thiosulphate,sodium citrate sucrose agar and bromothymol blue.
It is sterilisation is by autoclaving.

Wilson Blair Medium-Uninoculated

Its a selective and differential medium.

It contains peptic digest of animal tissue,beef extract,dextrose,disodium phosphate,ferrous sulphate,bismuth sulphate indicator,brilliant green.

Sterilization is by autoclaving.
Use:For isolating Salmonella species.
Its differential because H2S producing bacteria will produce black colonies and non H2S producing bacteria green colonies.

Comparison between Wilson blair medium and TCBS agar

The wilson blair medium shows colonies which are black for S.typhi and green for the S.paratyphi,while the V.cholerae shows yellowish colonies which later become green.

Also TCBS is little transparent than W-B. medium.

Uninoculated Lowenstain-Jensen medium

This is the selective medium for Mycobacterium tuberculosis.

It contains Egg,aspergin,peptone,agar,etc

the colonies appeare after 2-8 weeks which are yellow in colour.

Muller Hilton agar plate with Antibiotic sensitivity testing.

Its a special type medium which contains Beef extract,casein hydrolysate,starch and agar.

Its sterilised by autoclaving

Its used for antibiotic sensitivity testing.


1 comment:

  1. nice ones.. how about neisseria mening. in thayer hilton agar.. that would be a nice addition to this helpful collection..
    and thanks a lot