Gram Positive and Gram Negative Bacteria Overview

Study Notes

Structure of Gram-Negative Bacteria

Typical Gram-negative bacteria possess a peptidoglycan layer varying from 2 to 7 nm thick and an outer membrane measuring 7 to 8 nm thick.
A periplasmic space exists between the plasma membrane and the outer membrane, distinct within Gram-negative bacteria.

Gram Stain and Bacterial Classification

The Gram stain is vital in microbiology for bacterial taxonomy and identifying microorganisms clinically.
Initial studies using Bacillus subtilis and Escherichia coli successfully differentiated Gram-positive from Gram-negative bacteria.
Conventional models of bacterial cell walls may not accurately reflect all bacterial types, indicating complex cell wall classifications.

Bacterial Cell Envelope Theories

Lain Sutcliffe suggests shifts in bacterial cell envelope topologies, highlighting that some Gram-positive bacteria might actually be diderms, while Gram-negative species may be monoderms.
Escherichia coli exemplifies Gram-negative bacteria with dual layers consisting of a thin peptidoglycan and an outer membrane.

Peptidoglycan Structure

Peptidoglycan is a fundamental component of bacterial cell walls, forming a mesh-like structure called the peptidoglycan sacculus.
Lipoteichoic acids, a type of teichoic acid, are covalently linked to the plasma membrane.

Functions of Teichoic Acid

Provides a negative charge to the cell wall.
Anchors the cell wall to the plasma membrane, aiding in cell envelope structure.
Protects against harmful substances like antibiotics during cell division.
Facilitates ion uptake and adhesion of pathogenic species to host tissues.

Periplasmic Space Characteristics

The periplasmic space measures 30 to 70 nm wide and constitutes 20 to 40% of total cell volume in Gram-negative bacteria.
Contains various proteins, including transport proteins and exoenzymes that hydrolyze polymers for nutrient acquisition.

Functions and Components of Periplasm

Participates in energy production, peptidoglycan, and outer membrane synthesis.
Engages in the modification of toxic compounds.
Houses chemoreceptors that regulate chemotaxis responses.

Features of Gram-Negative Cell Walls

Gram-negative bacteria belong to the Firmicutes and Actinobacteria phyla.
Their outer membrane is complex, featuring a thin peptidoglycan layer situated within the periplasm.
Braun's lipoprotein links the outer membrane to the cell, incorporating lipopolysaccharides into its structure.

Description

Learn about the distinct layers, periplasmic space, and significance of Gram stain in microbiology. Understand the differences between Gram positive and Gram negative bacteria. Explore how Gram stain has impacted bacterial taxonomy and identification in clinical settings.