Unit 1

MICROBIOLOGY

Definition of Microbiology

  • Microbiology is defined as the study of microorganisms.
  • Microorganisms can include:
    • Prions: Infectious agents composed of protein.
    • Viruses: Acellular entities that require a host's cellular machinery to reproduce.
    • Bacteria: Prokaryotic microorganisms that may be beneficial or pathogenic.
    • Protozoa: Eukaryotic single-celled organisms, often motile and capable of causing diseases.
    • Algae: Photosynthetic eukaryotes that can be unicellular or multicellular.
    • Fungi: Eukaryotic organisms including yeasts and molds.
    • Helminths: Parasitic worms that can infect humans and other animals.

Visual Variation of Microorganisms

  • Microorganisms display variation in size and shape, observable microscopically.
  • They also vary invisibly in their metabolic capabilities.

MICROBIAL STRUCTURE

  • Prions: No cellular structure; consist solely of misfolded proteins.
  • Viruses: Composed of nucleic acid (RNA or DNA) enclosed in a protein coat.
  • Microbial Cells:
    • Prokaryotic Cells: Lack a defined nucleus and membrane-bound organelles.
    • Eukaryotic Cells: Have membrane-bound organelles including a defined nucleus.

MAIN PARTS OF ALL CELLS

  • Key components present in both prokaryotic and eukaryotic cells include:
    • Cell membrane
    • Cytoplasm
    • Genetic material (DNA/RNA)
    • Ribosomes for protein synthesis

PROKARYOTE VS. EUKARYOTE

  1. Prokaryotes: (Greek: before the nucleus)
    • Single-celled organisms (e.g., bacteria).
    • Simple structure without a nucleus.
    • Typically range from \text{1-10 μm} across.
    • DNA is circular and resides in the nucleoid.
    • No membrane-bound organelles present.
    • Replication and protein synthesis not spatially separated.

a. Examples of Prokaryotes: Bacteria, including cyanobacteria.

  1. Eukaryotes: (Greek: true nucleus)
    • Can be unicellular or multicellular organisms (e.g., fungi, plants, animals).
    • Complex structure with a defined nucleus.
    • Typically range from \text{10-100 μm} across.
    • DNA is coiled linear strands complexed with proteins, located in the nucleus.
    • Membrane-bound organelles are present.
    • Spatially separated mechanisms for replication and protein synthesis.

b. Examples of Eukaryotes: Protista, fungi, plants, animals.

COMPARISON OF PROKARYOTIC AND EUKARYOTIC CELLS

  • Cellular Characteristics:
    • Organisms:
    • Prokaryotic Cells: Bacteria (including cyanobacteria).
    • Eukaryotic Cells: Protista, fungi, plants, animals.
    • Cell Size:
    • Prokaryotic Cells: Usually \text{1-10 μm} across.
    • Eukaryotic Cells: Usually \text{10-100 μm} across.
    • Oxygen Requirement:
    • Prokaryotic Cells: Varies; some are anaerobic.
    • Eukaryotic Cells: Typically aerobic.
    • Membrane-bound Organelles:
    • Prokaryotic Cells: No.
    • Eukaryotic Cells: Yes.
    • Ribosomes:
    • Prokaryotic Cells: Present.
    • Eukaryotic Cells: Present.
    • DNA Form:
    • Prokaryotic Cells: Circular.
    • Eukaryotic Cells: Coiled linear strands, complexed with protein.
    • DNA Location:
    • Prokaryotic Cells: Located in nucleoid.
    • Eukaryotic Cells: Located in nucleus.
    • DNA Length:
    • Prokaryotic Cells: Short.
    • Eukaryotic Cells: Long.
    • Protein Synthesis:
    • Prokaryotic Cells: RNA and protein synthesis not spatially separated.
    • Eukaryotic Cells: RNA and protein synthesis spatially separated.
    • Membranes:
    • Prokaryotic Cells: Some.
    • Eukaryotic Cells: Many.
    • Cytoskeleton:
    • Prokaryotic Cells: No.
    • Eukaryotic Cells: Yes.
    • Cellular Organization:
    • Prokaryotic Cells: Single cells or colonies.
    • Eukaryotic Cells: Some single-celled, most multicellular with specialized cells.

SIZE COMPARISON OF MICROSCOPIC OBJECTS

  • Relative Sizes:
    • A typical virus measures about \text{100 nm} (nanometers).
    • A typical bacterium measures approximately \text{1 μm} (micrometer).
    • A plant or animal cell typically measures between \text{10–100 μm}.
    • An object must measure about \text{100 μm} to be visible without a microscope.

VIRUSES

  • Coronavirus Family:
    • Can cause respiratory infections including:
    • Common cold.
    • Severe Acute Respiratory Syndrome (SARS).
    • Middle East Respiratory Syndrome (MERS).
    • Viewed under a Transmission Electron Microscope (TEM).
  • Ebolavirus (Filovirus Family):
    • Visualized using TEM.

KINGDOM MONERA

  • Example: Helicobacter pylori cells, known to cause stomach ulcers.

KINGDOM PROTISTA

  • Example: Giardia lamblia, an intestinal protozoan parasite causing severe diarrhea in humans and mammals.

KINGDOM FUNGI

  • Example: Candida albicans, a unicellular fungus causing:

    • Vaginal yeast infections.
    • Oral thrush, common in infants.
    • Morphology similar to coccus bacteria, but considered eukaryotic due to the presence of nuclei and larger size.

  • Microscopic Fungi:

    • Large colonies often visually observable, such as moldy oranges.

KINGDOM ANIMALIA

  • Example: Taenia saginata (beef tapeworm):
    • Infects both cattle and humans; eggs are microscopically small yet adult worms can grow to \text{4–10 m} in length, residing in the digestive system.
  • Dracunculus medinensis:
    • Adult guinea worm removed through lesions in the skin.

SIGNIFICANCE OF MICROBIOLOGY

  • Understanding the role of various microorganisms is critical for disease prevention, food safety, biotechnology, and environmental health.

TYPES OF DISEASE

  • Many diseases have multifactorial origins. Examples include:
    • Cancer
    • Diabetes
    • Dementia
    • Rickettsial infections
    • Thalidomide syndrome in babies
    • Porphyria
    • Allergies
    • COVID-19
    • Some diseases may remain unexplained despite medical consultation.

RESIDENT FLORA

  • Definition: Normal microbiota present in various areas of the body, interacting with the host.
    • Transients: Temporary microbes present.
    • Residents: Permanent microbial inhabitants of the body.
    • Most body areas in contact with the outside environment harbor resident microbes, while internal organs are typically sterile.
  • Beneficial roles of bacterial flora in preventing overgrowth of harmful microbes through a mechanism called microbial antagonism.

CONTACT, COLONIZATION, INFECTION, DISEASE

  • Normal (resident) flora: The collective of microbes living symbiotically with the host.
  • Infection: The invasion of pathogens leading to disease.
  • Pathogen: A disease-causing microorganism.
  • Infectious Disease: A clinically evident disease resulting from infection by a pathogen.