Problem 57 - Objective Biology for NEET

Question

A bacterial cell was taken and gram staining was done and observed that it did not take up gram stain such a bacteria is known as (a) Gram positive (b) Gram negative (c) Non-effective to gram stain (d) None of these

Step-by-Step Solution

Answer

(b) Gram negative

Step 1: Understanding Gram Stain

Gram stain is a method of staining used in microbiology to differentiate bacterial species into two large groups (Gram-positive and Gram-negative). The name comes from the Danish bacteriologist Hans Christian Gram, who developed the technique. The method is based on the ability of bacteria to retain the crystal violet stain.

Step 2: Identifying the Bacteria

The exercise tells us that the bacteria did not retain the gram stain. This is indicative of the characteristics of a Gram-negative bacterium. Gram-negative bacteria do not retain the violet stain but instead turn pink from a counterstain.

Key Concepts

Gram Positive

Gram-positive bacteria are a group of bacteria that retain the crystal violet stain used in the Gram stain technique, appearing purple under the microscope. The reason for this retention is the thick peptidoglycan layer in their cell walls, which traps the stain. This peptidoglycan layer is much thicker in Gram-positive bacteria compared to Gram-negative bacteria, which is a distinguishing feature.

Some key characteristics of Gram-positive bacteria include:

• High susceptibility to antibiotics like penicillin.
• Less complex cell walls compared to Gram-negative bacteria.
• Presence of teichoic acids in the cell wall, which help in the retention of the stain and contribute to their rigid structure.

Examples of Gram-positive bacteria include Staphylococcus, Streptococcus, and Bacillus species. These bacteria are commonly found in the environment and can cause diseases, but they also play essential roles in natural processes and industrial applications.

Gram Negative

Gram-negative bacteria don't retain the crystal violet stain and instead take up the counterstain, typically safranin, which makes them appear pink or red under a microscope. This difference in staining is due to their complex cell wall structure.

The cell wall of Gram-negative bacteria is characterized by:

• A thinner peptidoglycan layer compared to Gram-positive bacteria.
• An outer membrane that contains lipopolysaccharides, contributing to its structural complexity.
• Higher resistance to certain antibiotics, often making them more challenging to treat.

These structural differences also contribute to their ability to withstand harsh environments and contribute to their pathogenicity in certain species. Common examples of Gram-negative bacteria include Escherichia coli, Pseudomonas aeruginosa, and Salmonella species. Understanding these bacteria's unique characteristics helps in designing effective treatments and in studying various biological processes.

Gram Stain Technique

The Gram stain technique is a fundamental method used in bacteriology to classify bacteria into two main groups: Gram-positive and Gram-negative. This differentiation is crucial because it helps guide the treatment of bacterial infections.

The Gram stain process involves several steps:

• Application of a primary stain (crystal violet), which penetrates all bacterial cells.
• Adding iodine, which acts as a mordant to fix the stain inside the cells.
• Decolorization with alcohol or acetone, which differentiates the bacteria based on cell wall properties.
• Finally, a counterstain (usually safranin) is applied so that Gram-negative bacteria, which lost the crystal violet stain, can be seen as pink.

This technique was developed by Hans Christian Gram in 1884 and remains an essential laboratory procedure. It is not only a quick and simple way to classify bacteria but also helps in understanding the structural differences between bacteria, thereby influencing antibiotic treatment choices.