BIOS242 Lab 5
Name:
Lab 5: Differential Staining
Learning Objectives:
 Explain the principle of differential staining
 Apply differential staining to identify bacteria
Differential stain uses two or more stains to specifically stain certain structures or cellular components which cannot be easily observed using simple stains.
Differential staining principles are based upon the specific chemical nature and composition of cellular components and therefore, different structures are
observed using different stains and staining procedures. Differential staining often becomes the basis of identification of the bacteria in clinical labs.
In this lab, we will learn about four separate staining procedures.
 Gram Staining
 Endospore Staining
 Capsule Staining (Special Staining)
Exercise 1: Gram Staining
Gram staining is used to identify cells based on the differences of the cell wall. While some bacteria may contain a thick layer of peptidoglycan that forms a thick
rigid cell wall (Gram positive), other bacteria have a very thin layer of peptidoglycan forming a thin cell wall sandwiched between two cell membranes (Gram
negative). The outer membrane is rich in
lipopolysaccharides (LPS). Gram staining
takes advantage of these differences in the
cell wall of bacteria. Using two different
stains that offer a lot of contrast, bacteria
containing a thick cell wall are stained