Chapter 2, Problem 12RQ

Summary Introduction

To review:

The importance as well as limitations of Gram staining for bacterial taxonomy.

Introduction:

Chemical dyes can be used to distinguish between different strains of bacteria. The ability of the colored dye to absorb light of a particular wavelength and also chemically bind to the key components of the bacterial cell can be used to identify various bacterial features. The identification of these features can also be used in classification.

Gram staining is widely used to detect the bacteria and their nature as well as the type inside the laboratory. Gram staining classifies bacteria into two major classes depending on whether they absorb the crystal violet or not. The taxa Firmicutes is Gram-positive as it absorbs the crystal violet while the taxa Proteobacteria is Gram-negative as it does not absorb the crystal violet. The absorption depends on whether the bacterial cell has peptidoglycan layers or not.

The use of Gram staining can help distinguish between Gram-negative bacteria like Proteobacteria, Escherichia coli, and related intestinal bacteria and Gram-positive bacteria like Firmicutes, Clostridium, and Enterococcus. It can help us understand the normal gut microflora as well as the detection of pathogenic bacteria like Streptococcus pneumonia in pus.

However, limitations of Gram staining are the results that may be variable in some species. Variable results are also evident in some species like Bacillus belonging to phylum Firmicutes. The result depends upon the stage of microbial growth and environmental conditions. The microorganism possessing a variable type of cell wall is also not distinguished by the Gram staining.