Introduction to Medical Microbiology

Introduction to Medical Microbiology

• Microbiology studies microscopic living organisms.
• The course covers various aspects of microbiology, including physiology, ecology, and taxonomy.
• Key figures in microbiology include:
  • Ignaz Semmelweis: Advocated handwashing and instrument disinfection
  • Louis Pasteur: Invented pasteurization
  • Joseph Lister: Introduced antiseptic surgery using phenol
  • Robert Koch: Proved the Germ Theory using Koch's Postulates
  • Dmitri Ivanovski: Laid the foundation for virology
  • Paul Ehrlich: Developed chemotherapy with Salvarsan
  • Alexander Fleming: Discovered penicillin
• The development of the electron microscope in 1931-38 by Max Knoll and Ernst Ruska revolutionized microbiology.

Importance of Microbiology

• Basic Science: Contributes to the Theory of Evolution, especially bacterial origins.
• Agriculture: Vital for photosynthesis and decomposition, playing a key role in nutrient cycling.
• Food Microbiology: Microorganisms are used in food production, fermentation, and preservation.
• Public Health and Epidemiology: Microorganisms are responsible for infectious diseases.
• Healthy Microbiome: Microorganisms play a beneficial role in maintaining a healthy human microbiome.

Bacteria

• Bacteria are prokaryotic organisms lacking a formal nuclear structure.
• They have a single molecule of DNA, usually circular (bacterial chromosome).
• Some bacteria contain extra-chromosomal DNA called plasmids.
• Bacteria are smaller than eukaryotic cells, typically less than 2 micrometers in diameter.
• They are responsible for various human and animal infections, such as syphilis, pharyngitis, endocarditis, and anthrax.

Fungi

• There are approximately 1.5 million fungal species on Earth, with about 300 known to cause disease in humans.
• Fungi are eukaryotic organisms.
• They are commonly found in soil, on plants, and indoor surfaces.
• Fungal infections can range from mild skin infections to serious lung and bloodstream infections.

Parasites

• A parasite is an organism that lives on or in a host and obtains sustenance at the expense of its host.
• There are three main classes of parasites that can cause disease in humans:
  • Protozoa (microscopic, single-celled organisms)
  • Helminths (large, multicellular organisms)
  • Ectoparasites (external parasites like ticks, fleas, lice, and mites).
• Protozoa can multiply inside humans, contributing to infection development.
• Helminths, in their adult form, cannot multiply inside humans.
• Ectoparasites attach or burrow into the skin and remain for extended periods.

Taxonomy

• Taxonomy is a system for organizing, classifying, and naming living organisms.
• It focuses on classification and nomenclature.
• The three-domain system (Archaea, Bacteria, Eukarya) developed by Carl Woese in 1990 is currently used in modern biology.

Domain: Bacteria

• Taxonomic classification within the Bacteria domain follows a hierarchical structure:
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species
  • Subtype (if applicable)
• Example:
  • Phylum: Proteobacteria
  • Class: Gamma proteobacteria
  • Order: Coccidioides
  • Family: Enterobacteriaceae
  • Genus: Escherichia
  • Species: E.coli
  • Subtype: Serovar O157

Species

• The species is the fundamental unit of taxonomic classification, representing a specific recognized type of organism.
• For sexually reproducing organisms, a species is defined by reproductive compatibility.
• Organisms within a genus generally share 93% similar rRNA.
• Organisms within a species generally share 97% similar rRNA.
• This definition is not applicable to many microbial species, including bacteria, as they do not reproduce sexually.

Species in non-sexually dividing organisms

• A population of cells with similar characteristics is defined as a species.
  • Clone: A population of cells derived from a single cell (genetically identical)
  • Strain: A subgroup within a species possessing distinct characteristics that differentiate it from other subgroups (not genetically identical)

Binomial System of Nomenclature

• Scientific or Systematic Name: - Genus name followed by the species name - Italicized or underlined - Genus name capitalized, can be abbreviated - Species name never abbreviated - Genus name can be used alone, species name cannot - Example: Bacillus subtilis or B. subtilis

Introduction to Microbiology

• Microbiology is a study of microscopic living organisms, like bacteria, fungi and viruses
• The subject covers their physiology, ecology and taxonomy

History of Microbiology

• 1847: Ignaz Semmelweis implemented mandatory hand washing and chlorine disinfection of instruments to prevent the spread of infections
• 1864: Louis Pasteur invented Pasteurization, a process of heating liquids to kill pathogens and prevent spoilage
• 1867: Sir Joseph Lister used phenol to sterilize surgical instruments, wounds, and the surrounding environment, reducing surgical infections
• 1876: Robert Koch proved the Germ Theory, demonstrating that specific microbes cause specific diseases. Koch's Postulates defined the criteria for proving a microbe as the cause of a disease
• 1892: Dmitri Ivanovski discovered viruses through filtration experiments, laying the groundwork for Virology
• 1910: Paul Ehrlich developed Salvarsan, an arsenic derivative, to treat syphilis, marking the beginning of chemotherapy
• 1928: Alexander Fleming discovered penicillin, a substance produced by Penicillium notatum, with antibacterial properties
• 1931-1938: Max Knoll and Ernst Ruska invented the prototype of the electron microscope

Importance of Microbiology

• Basic Science: Microbes play a key role in the theory of evolution, showcasing the early origins of life.
• Agriculture: Microbes are essential for photosynthesis and decomposition, vital for nutrient cycling.
• Food Microbiology: Microbes are used in various food production processes like fermentation and preservation.
• Public Health and Epidemiology: Microbiology helps us understand the mechanisms of infectious diseases and their spread.
• Healthy Microbiome: The human body carries a diverse community of beneficial microbes, critical for overall health.

Bacteria

• Bacteria are prokaryotes, lacking a nucleus
• Their DNA is often circular (bacterial chromosome) and sometimes accompanied by extra-chromosomal DNA (plasmids)
• They are smaller than eukaryotic cells, typically less than 2 micrometres in diameter
• Bacteria cause a wide range of human and animal infections.

Fungi

• Fungi are eukaryotic organisms
• They exist in diverse environments, including soil, plants, and indoor surfaces
• While most fungi are harmless, about 300 species are known to cause diseases in humans
• Fungal diseases can be mild, like skin infections, or serious, like lung or bloodstream infections.

Parasites

• Parasites are organisms that live on or inside a host and obtain nourishment from them.
• There are three main classes of human parasites:
  • Protozoa: microscopic, single-celled organisms
  • Helminths: larger, multicellular organisms, visible to the naked eye in their adult stages
  • Ectoparasites: external parasites that attach or burrow into the skin

Viruses

• Viruses are genetic elements that can replicate only inside living cells, called obligate intracellular parasites.
• They consist of a nucleic acid core (DNA or RNA) surrounded by a protein coat (capsid).
• Some viruses have an additional lipid envelope.
• Viruses can cause diseases in various organisms, including humans, animals, bacteria, and plants.

Virus Classification

• Viruses are classified by:
  • the host they infect
  • presence or absence of a lipid envelope
  • symmetry of the nucleocapsid
  • type of nucleic acid (DNA or RNA)
  • number and structure of nucleic acid strands