Material

• Microscope slide with heat fixed sample.
• Set of dyes. Methyl-Violet and Safranin.
• Alcohol-Acetone decolorizer.
• Metal tweezers.
• Stopwatch.

Procedure

1.Immerse the microscope slide in methyl violet for 1 minute.
2.Wash with water and leave it to drain.
3.Immerse it in lugol’s iodine. Leave it for 1 minute.
4.Wash with water and leave it to drain.
5.Discolor it with alcohol-acetone for 15 seconds.
6.Take it out and immediately immerse it in safranin to compare it. Leave it in for 1 minute.
7.Wash with water and dry it with filter paper.

In the microscopic observation the Gram-positive bacteria have been dyed purple and the Gram-negative bacteria are pink.

Gram-negative cocci	Gram-positive cocci	Gram-positive cocci and Gram-negative bacilli

Gram-negative/positive cocci Marta Estévez, Minerva Henares  2022-23	Gram-positive cocci Ana Climent, Ana Peñafiel 2022-23	Gram-positive cocci

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