MIC456 Microscopy

TYPES OF STAINING METHODS

2. Special staining – Capsule staining
▪ Capsule is a semi-rigid polysaccharide layer produced by some
bacteria as protection against

▪ Phagocytosis – virulence factor
▪ Dryness
▪ Chemicals – such as detergent
▪ Viruses

▪ Since capsule does not readily retain dyes, negative stainig methos is often used
whereby the cells are stained with safranin or crystal violet (basic dye) prior to
flooding the smear with Indian ink to stain the background

▪ Capsules appear as a halo ring around the red-stained dye/ purple-stained dye

Steps in Capsule staining

1. Place a drop of Indian ink on one end of your slide.
2. Then add your bacteria to the Indian ink and make a smear (like a blood smear)
3. Air-dry the smear BUT DO NOT HEAT FIX
4. Flood the smear with safranin for 30 seconds to 1 minute – be gentle because the

smear has not been heat-fixed
5. Rinse the stained smear and allow the slide to air-dry.
6. Observe under a microscope.

https://goo.gl/images/uU3CT9



LEARNING OUTCOMES

At the end of this topic, students should be able to

▪ Understand the concept of microscopy
▪ Differentiate the different types of microscopes
▪ Describe sample preparation strategies
▪ Explain the process and theory behind staining techniques in

microbiology

ANY QUESTIONS?

Reading assignment:
• Functional anatomy of prokaryotes
• Tortora pg 98-119