Gram Staining in Curd Sample

1. Take two clean glass slides and wash them properly.

2. Place a small amount of curd sample in a beaker.

3. Using a dropper, take a drop of the liquid part of the curd and place it on one slide.

4. Use the second slide to spread the sample at a 45° angle to form a thin layer (smear).

5. Allow the smear to air-dry completely.

6. Heat-fix the smear by passing the slide gently over a spirit lamp flame for about 30 seconds.

7. Stain the slide with crystal violet and let it retain the stain for a short time.

8. Rinse off the excess stain with water and let the slide dry for 1 minute.

9. Apply iodine solution to the smear (mordant) and allow it to retain the stain.

10. Rinse off the extra iodine solution and let the slide dry again.

11. Add a decolourising agent (ethanol) for a few seconds to remove excess primary stain.

12. Rinse immediately with water and let the slide dry.

13. Apply safranin solution (counterstain) and let it remain for a short time.

14. Rinse off the extra safranin and allow the slide to air dry completely.

15. Once dried, the Gram-stained slide is ready.

16. Observe the sample under a microscope to identify Gram-positive and Gram-negative bacteria.

The curd sample appeared violet or purple in colour after Gram staining, indicating the presence of Gram-positive bacteria.
The bacterial species observed under the microscope were Lactobacillus and Streptococcus, both of which are Gram-positive, rod- and cocci-shaped bacteria commonly found in curd.