From vaccine development to antibiotic discovery and food safety testing, microbiology has become one of the most influential sciences in healthcare and industry. What once began as simple observations of tiny “animalcules” has evolved into a sophisticated field that studies organisms invisible to the naked eye. UNIT 1 introduces students to the history, structure, growth, and observation of microorganisms, laying the groundwork for advanced biological and pharmaceutical studies.
Today, microbiology impacts medicine, agriculture, environmental science, and biotechnology more than ever before.
History of Microbiology: From Discovery to Modern Labs
The story of microbiology began with Antonie van Leeuwenhoek, who first observed microorganisms using handcrafted microscopes. Later, Louis Pasteur disproved spontaneous generation and introduced pasteurization, while Robert Koch established the germ theory of disease.
These discoveries transformed medicine by linking microbes to infections and guiding the development of sterilization, vaccination, and antibiotics.
Branches, Scope, and Importance of Microbiology
Major Branches
Microbiology today includes several specialized areas:
- Bacteriology
- Virology
- Mycology
- Parasitology
- Immunology
Scope and Importance
Its applications include:
- Disease diagnosis
- Vaccine production
- Food preservation
- Drug manufacturing
- Environmental protection
Microbiology supports nearly every aspect of modern healthcare and biotechnology.
Introduction to Prokaryotes and Eukaryotes
Key Differences
Microorganisms are broadly classified into prokaryotes and eukaryotes.
| Feature | Prokaryotes | Eukaryotes |
|---|---|---|
| Nucleus | Absent | Present |
| Size | Smaller | Larger |
| Organelles | Absent | Present |
| Examples | Bacteria | Fungi, protozoa |
Bacteria, the focus of this unit, belong to prokaryotes.
Ultra-Structure and Morphological Classification of Bacteria
Bacterial Cell Structure
Bacterial cells consist of:
- Cell wall
- Plasma membrane
- Cytoplasm
- Ribosomes
- Nucleoid
- Flagella or pili (in some species)
These structures help bacteria survive and reproduce in diverse environments.
Morphological Classification
Based on shape, bacteria are grouped into:
- Cocci (spherical)
- Bacilli (rod-shaped)
- Spirilla (spiral-shaped)
- Vibrios (comma-shaped)
Shape and arrangement help in identification and diagnosis.
Nutritional Requirements and Culture Media
Basic Requirements for Growth
Bacteria require:
- Carbon source
- Nitrogen source
- Minerals
- Vitamins
- Water
Raw Materials Used in Culture Media
Common components include:
- Peptone
- Meat extract
- Agar
- Sugars
- Salts
These materials provide nutrients and support bacterial multiplication.
Physical Parameters for Growth
Environmental conditions strongly affect growth:
- Temperature
- pH
- Oxygen
- Moisture
- Osmotic pressure
For example, pathogens often grow best at human body temperature (37°C).
Bacterial Growth Curve Explained
Phases of Growth
When bacteria grow in a closed system, they follow a characteristic growth curve:
- Lag phase
- Log (exponential) phase
- Stationary phase
- Death phase
Understanding these phases helps in antibiotic testing and fermentation technology.
Isolation and Preservation of Pure Cultures
Isolation Methods
To study bacteria accurately, pure cultures are needed. Methods include:
- Streak plate
- Spread plate
- Pour plate
Preservation Techniques
Cultures can be stored by:
- Refrigeration
- Freeze-drying
- Cryopreservation
These techniques maintain bacterial strains for research and industrial use.
Cultivation of Anaerobes
Anaerobic bacteria grow without oxygen and require special techniques.
Common Methods
- Anaerobic jars
- Gas packs
- Reducing agents
Such methods are essential for studying pathogens that thrive in oxygen-free environments.
Quantitative Measurement of Bacterial Growth
Total Count
Counts all cells, both living and dead, using microscopic or electronic methods.
Viable Count
Counts only living cells capable of forming colonies using plate count techniques.
Both methods are crucial for assessing microbial load in clinical and industrial samples.
Modern Microscopy: Seeing the Invisible
Phase Contrast Microscopy
Enhances contrast without staining, ideal for observing living cells.
Dark Field Microscopy
Produces bright images on a dark background, useful for thin or motile organisms.
Electron Microscopy
Provides extremely high resolution to study ultrastructure.
- Transmission Electron Microscope (TEM)
- Scanning Electron Microscope (SEM)
These tools reveal fine cellular details invisible to light microscopes.