Gram Stain ProcedureEssay on

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Purpose: Why do people who drink water from the river without boiling develop stomach problems?

Hypothesis: Boiled water will have no indicator bacteria (for example Escherichia coli) as compared to water from a nearby river.

Apparatus used

i. Petri dish

ii. Inoculation loop

iii. Source of flame

iv. Grain stain solutions (crystal violet, iodine, alcohol, and carbon fuchsin)

v. A reliable source of water (running tap water)

vi. Sterile slides

Gram Stain procedure

i. On a sterile slide, add a loopful of distilled water.

ii. Inoculating loop is used to transfer a colony from a labeled petri dish culture onto the slide.

iii. The culture is spread to an even thin film with the inoculation loop, to a circle of about 1cm diameter.

iv. The culture is dried of air and put over a gentle flame, repositioning the slide in a spherical motion to heat evenly.

v. Two droplets of crystal Violet stain are mixed to the fixed culture and left to rest for a minute then poured off and the stain rinsed with flowing tap water to clean the stain.

vi. To cover the fixed culture, two drops of iodine solution are added and allowed to stand for a minute and slide rinsed with running tap water. Excess water is dried off from the surface.

vii. Two drops of alcohol (decolorizing solution) are added and rinsed with running tap water after ten seconds.

viii. Counter stain with Carbon fuchsine for one minute and wash off with running tap water.


The culture inoculated with water obtained from the river without boiling stains purple.


Purple stain indicates the gram-negative bacteria such as Escherichia coli, which indicates the presence of fecal contamination of water. From this, I have learned that it is essential to boil water before use for drinking. In this experiment, the apparatus used could have been contaminated by other samples.

August 09, 2023

Food Health


Biology Illness

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