BMS2400-Yoganathan-bacteria-1

Medical Microbiology Introduction

• Instructor: Dr. Sabesan Yoganathan

• Course Code: SAH-330

• Contact: yoganats@stjohns.edu

• Confidentiality: Document is for classroom use only, do not share externally.

Bacteria Overview

Basic Concepts (Chapter 21)

Pathogenesis of Bacterial Infections (Chapter 22)

• Staphylococcus aureus: Gram-positive bacteria

• Peptidoglycan: Key component of bacterial cell wall

Characteristics of Bacteria

Key Features of Bacteria

• Appearance:

  • Shape (coccus, bacillus, etc.)

  • Gram stain results

• Growth Requirements:

  • Specific nutrients and selective media requirements

• Metabolism:

  • Types include aerobic, anaerobic, and facultative

• Biochemistry:

  • Includes proteases and various enzymes

• Antigenicity:

  • Mechanisms of immune recognition

• Genotype:

  • Methods like DNA hybridization, PCR, sequencing of 16S rRNA

Bacterial Cell Structure

Cell Wall Composition

• Gram-positive Bacteria:

  • Thick peptidoglycan layer (50%)

  • No outer membrane, susceptible to cell wall disruption

• Gram-negative Bacteria:

  • Thin layer of peptidoglycan, double membrane structure

  • Outer membrane contains high lipid content, resistant to disruption

Functions of Bacterial Cell Wall

• Maintains Shape and Rigidity

• Protects Against Osmotic Lysis

• Enables Attachment to Surfaces

• Provides Protection from the Immune System

Gram Staining Technique

• Steps:

  1. Crystal violet application

  2. Gram iodine application

  3. Application of decolorizer (alcohol/acetone)

  4. Application of safranin red

• Results:

  • Gram-positive bacteria appear purple

  • Gram-negative bacteria appear red

Important Notes on Gram-Staining

• Some gram-positive bacteria can be easily decolorized, others retain the crystal violet color.

• Spatial arrangement (shape and clustering) is vital for interpreting results.

Bacterial Shapes and Configurations

Common Shapes

• Coccus: Circular bacteria

• Bacillus: Rod-shaped bacteria

• Spirilla: Spiral-shaped bacteria

• Variants: Curved forms (Vibrio, Spirillum)

• Grouping:

  • Diplo-: pairs

  • Strepto-: chains

  • Staphylo-: clusters

Peptidoglycan Structure

Composition and Function

• Polymers of N-acetylmuramic acid and N-acetylglucosamine

• Rigid glycan chains cross-linked by peptide bridges

• Essential for maintaining bacterial cell integrity and shape

Bacterial Metabolism

Types of Metabolic Processes

• Catabolism vs. Anabolism:

  • Catabolism involves breakdown of complex molecules to generate energy

  • Anabolism involves synthesis of complex molecules from simpler ones

Energy Production Processes

• Glycolysis (Fermentation)

• Aerobic Respiration

• Anaerobic Respiration

• Pentose Phosphate Pathway: Generates NADPH

Transport and Secretion Mechanisms

Transport Systems

• Facilitated Diffusion

• Active Transport: Involves binding proteins and ATP

• Secretion Systems: Include multiple types for gram-positive and gram-negative bacteria

  • Examples include Type I to Type IV secretion

Genetic Material Exchange

Mechanisms of Genetic Transfer

• Transformation: Uptake of naked DNA from the environment

• Transduction: Transfer of DNA via bacteriophages

• Conjugation: Transfer of plasmid DNA through direct contact

• Transposition: Movement of transposable elements within the DNA

Plasmids and Their Functions

• Plasmids: Self-replicating genetic elements

• Can contain genes for antibiotic resistance and virulence factors

Mutations and Their Impact

Types of Mutations

• Substitution (Transition and Transversion)

• Frameshift Mutations: Caused by insertions or deletions

• Consequences: Effect on protein synthesis and function, potential for antibiotic resistance

Lac Operon and Gene Regulation

Structure and Function

• Regulatory Gene (lacI): Controls transcription

• Operon Components: lacZ, lacY, lacA for lactose metabolism

• Control Mechanisms: Inducible and repressible systems involving various proteins and conditions