SLIDE
PREPARATION FROM CURD
Curd Sample Smear Preparation and Gram
Staining
INTRODUCTION
Curd
is a milk product formed by fermentation.
Fermentation is the activity of a genus of bacteria named as Lactobacillus.
Lactobacillus bacteria convert sugars into lactic
acid by means of fermentation.
Milk contains a sugar called lactose, a
disaccharide (compound sugar) made by the glycosidic bonding between glucose and
galactose (monosaccharide). Curd contains different types of bacteria such as cocci,
bacillus etc. By Gram staining method a differential stain is used for
demonstration of Gram positive and Gram negative bacteria. The Method for staining
bacteria is as under:
METHOD FOR PREPARATION OF SLIDE OF BACTERIA
1. Take a grease free
glass slide and draw a thin smear of curd sample with the help of another
slide.
2. Heat fix the smear.
3. Now put a few drops
of crystal violet and keep it for 2 minutes.
4. Next wash the
slide with tap water.
5. After washing put few
drops of Gram's Iodine on the smear and keep it for 2 minutes.
6. Wash again with tap
water.
7. Then put few drops
of Safranine on
the smear and keep it for 1 minute and wash.
8. Observe under
compound microscope.
Figure:
Gram Positive and Gram Negative Bacteria
OBSERVATIONS
1. Gram
Positive Cocci: Color-Purple
2. Gram
Negative Bacilli: Color-Red
