Yogurt

OBJECTIVE: The objective is to know how does the Gram stain and also to find bacteria that are called Lactobacillus and Streptococcus, that are G+ and G-

MATERIAL:

• Yogurt
• Ethanol
• Crystal violet
• Distilled water
• A bunsen burner
• 3 beakers
• Dropper
• Lighter
• Slide and cover slide
• Needle
• Lugol
• forceps
• Petri dish
• Microscope

PROCEDURE:

1. Take the needle and warm it up in the bunsen burner, and then, with the cold needle, take a sample of the yogurt
2. Put the sample on a slide and put some drops of distilled water. Also warm it up in the bunsen burner and with the help of a forceps until the water evaporate
3. Add two or three drops of crystal violet in the sample of yogurt and wait for one minute and a half. Then clean the slide with distilled water
4. Add also two or three drops of Lugol to seal the crystal violet and wait for one minute
5. After this minute clean the sample with distilled water to move away the excess of dye.
6. Then add ethanol to take away the dye of the G- and to see the G+

RESULTS:

The G+ are the ones that are dieying with a red colour and the G- are the ones that are transparent.

QUESTIONS:

1.  Explanation of Gran stain

Gram staining involves three processes: 

• staining with a water-soluble dye called crystal violet

• decolorization

• counterstaining

Due to differences in the thickness of a peptidoglycan layer in the cell membrane between Gram positive and Gram negative bacteria.

Gram positive bacteria retain crystal violet stain during the decolorization process, while Gram negative bacteria lose the crystal violet stain and are instead stained by the safranin in the final staining process.