Introduction to microbiology

INTRODUCTION TO MEDICAL MICROBIOLOGY

Overview

Medical Microbiology is a crucial aspect of medical science that focuses on the study of microorganisms capable of causing diseases in humans. This presentation outlines the foundational concepts, historical perspectives, and the significance of microbes in both beneficial and harmful senses.

Objectives

By the end of this presentation, you should be able to:

  • Describe basic concepts and definitions used in microbiology.
  • Explain the historical perspectives of microbiology.
  • Name and classify microbes.
  • Understand the principles of microbiology and their importance in clinical medicine practice.
  • Recognize the role of microbes in human welfare and health-related diseases.

Basic Concepts and Terminology

Definition of Microbiology

  • Microbiology is described as the study of living organisms that are of microscopic size.
  • Medical microbiology specifically refers to the study of microorganisms that can infect humans and cause diseases, alongside the prevention, diagnosis, and treatment of these infectious diseases.

Microorganisms

  • Micro-organisms are defined as minute living organisms that are individually too small to be seen by the naked eye.
  • The group comprises various entities such as:
    • Bacteria
    • Viruses
    • Fungi (yeasts and molds)
    • Protozoa
    • Microscopic algae
  • These microorganisms largely exhibit a small size, which necessitates using a microscope to view their structural characteristics in detail.

Characteristics of Microorganisms

  • All microorganisms possess a simple structure and lack cell differentiation into tissues, meaning that one cell constitutes a complete organism.
  • They are ubiquitous, existing everywhere in the environment.
  • Laboratory techniques for culturing and handling these organisms generally exhibit similarities regardless of the type of microorganism being studied.

Nomenclature of Microorganisms

System of Nomenclature

  • The nomenclature system currently used was established by Carolus Linnaeus in 1735.
  • Scientific nomenclature assigns each organism two names, referred to as binomial nomenclature:
    • Genus: The first name, always capitalized.
    • Specific Epithet: The second name, not capitalized.
  • Both names are either underlined or italicized.
  • For example: Staphylococcus aureus
Meaning Behind Scientific Names
  • Scientific names can indicate various attributes, such as:
    • Describing an organism
    • Honoring a researcher
    • Identifying the species' habitat
  • For example, in Staphylococcus aureus:
    • Staphylo- refers to the clustered arrangement of the cells.
    • -coccus indicates a spherical shape.
    • Aureus, meaning golden in Latin, describes the typical color of its colonies.
  • Another example is Escherichia coli, named after Theodor Escher, with coli referencing its typical habitat in the colon.

Classification of Microorganisms

Microbial Taxonomy

  • The classification system for microorganisms, known as microbial taxonomy, allows living organisms to be arranged into a hierarchical structure.
  • This taxonomy consists of several levels, wherein a specific organism is grouped according to a genus and species, as well as a family, order, class, and phylum.
  • Related phyla form a kingdom, while related kingdoms are grouped into a domain.

The Taxonomic Hierarchy

  • The major taxonomic hierarchy includes:
    • Domain: Eukarya, Archaea, Bacteria
    • Kingdom: Fungi, none assigned for archaea or bacteria
    • Phylum: Ascomycota
    • Class: Hemiascomycetes
    • Order: Saccharomycetales
    • Family: Saccharomycetaceae
    • Genus: Saccharomyces
    • Species: S. cerevisiae (Baker's yeast), Escherichia (e.g., E. coli)

Classification Methods

Microorganisms are classified based on several criteria such as:

  • Based on Plants or Animals: Aristotle's classification posited two kingdoms, Plantae and Animalia.
    • Plantae: Includes algae, fungi, and bacteria.
    • Animalia: Encompasses all animals including protozoa.
  • Cellularity: Organisms can be categorized as:
    • Non-cellular: E.g. Viruses
    • Unicellular: E.g. Protozoa, bacteria, certain algae and fungi
    • Multicellular: E.g. Fungi, algae
  • Nature of Nuclear Materials: Organisms can be divided into:
    • Prokaryotes: No true nucleus (e.g. Bacteria). Circular chromosomes are present without organelles like mitochondria.
    • Eukaryotes: Organisms with a true nucleus; nuclear material surrounded by a membrane, and possess regular chromosomes (e.g. Protozoa, algae, fungi, and animals).

Five Kingdom Concept

  • Proposed by Whittaker in 1969, this classification system is based on nutritional modes and cellular organization. The five kingdoms include:
    • Monera
    • Protista
    • Fungi
    • Plantae
    • Animalia

Eight Kingdom Concept

  • Introduced by Cavalier-Smith in 1987, this system divides microbes into two empires constituting eight kingdoms.

Three Domain System

  • Proposed by Carl Woese in 1978, organisms are classified