Medical Microbiology Introduction

Lecture 1: Introduction to Medical Microbiology

• Lecture presented by Dr. Rasha Mokhtar Elnagar, a Medical Microbiology and Immunology Associate Professor and Consultant
• Course covers the basics of Medical Microbiology, including definitions and classifications of microorganisms

Definitions

• Microbiology: The study of microorganisms that are too small to be seen without a microscope
• Microorganisms: Living organisms that require a microscope to be seen

Classification of microorganisms

• Acellular: Not composed of cells. Examples: viruses
• Cellular: Composed of cells
  • Prokaryotes: Lack a nucleus and membrane-bound organelles. Examples: bacteria
  • Eukaryotes: Have a nucleus and membrane-bound organelles. Examples: Fungi, protozoa, helminths

Classification of Bacteria

• Morphology (Shape & Arrangement): Bacteria are classified based on their shape and arrangement

  • Cocci: Spherical or oval cells
    • Diplococci: Pairs (e.g., Streptococcus pneumoniae)
    • Chains: Chains of cocci (e.g., Streptococcus pyogenes)
    • Grape-like clusters: Clusters of cocci (e.g., Staphylococcus aureus)
  • Bacilli: Rod-shaped bacteria
    • Curved/Comma-shaped: Curved or comma-shaped (e.g., Vibrio cholerae)
    • Club-shaped: Club-shaped (e.g., Corynebacterium diphtheriae)
    • Coccobacilli: Short rod-shaped (e.g. Haemophilus influenzae)
  • Spirochetes: Long, slender, spiral-shaped bacteria with coils (e.g. Treponema, Borrelia, Leptospira)

• Staining reaction: Gram stain, Acid-Fast stain

  • Gram-positive: Appear violet (e.g., Staphylococcus, Streptococcus, Clostridium)
  • Gram-negative: Appear red (e.g., Neisseria, Moraxella, Escherichia coli, Klebsiella, Vibrio, Haemophilus)
  • Acid-fast stain: Used to identify bacteria requiring this stain due to a waxy cell wall (e.g., Mycobacterium tuberculosis)

• Cell wall:

• Lacking cell wall: Mycoplasma

• Flexible cell wall: Spirochetes (e.g., Treponema)

• Rigid cell wall:

  • Filamentous Bacteria: Include those that produce antibiotics (e.g., Streptomyces)
  • Simple Unicellular: Includes some bacteria that are obligate intracellular parasites (e.g. Rickettsia, Chlamydia)
  • Free living: Generally free living bacteria

Medically Important Bacteria

• Diagram showing classifications: laking cell wall, rigid cell wall, flexible cell wall, gram positive, gram negative and specific shapes

Test Your Understanding

• Q1: Gram-positive bacteria have peptidoglycan in their cell walls
• Q2: Treponema pallidum is an example of spirochete bacteria
• Q3: Staphylococcus aureus is a gram-positive bacteria
• Q4: Neisseria species is a gram-negative cocci bacteria

Reference

• Lippincott Illustrated Microbiology 4th edition, Chapters 1