General Characteristics Of Microbes

Microorganisms

Microorganisms are tiny living organisms that are visible only under a microscope. They are present all around us and even inside our bodies. Despite their small size, microorganisms play a crucial role in our environment and in various biological processes. Microorganisms can be classified into two major types: Pathogenic and Non-Pathogenic.

Types of Microorganisms

1. Pathogenic Microorganisms

Pathogenic microorganisms are disease-causing organisms that can lead to infections in humans, animals, and plants.
These organisms can spread through direct contact, air, water, and contaminated surfaces.

Example: Mycobacterium tuberculosis causes tuberculosis and is transmitted through droplets of respiratory secretions from an infected person to an uninfected person.

2. Non-Pathogenic Microorganisms

Non-pathogenic microorganisms do not cause diseases and are often beneficial to humans.
Some non-pathogenic microorganisms play an essential role in maintaining homeostasis in the human body.
They are also widely used in the production of food, medicines, and other commercial products.

Example: Intestinal flora aids digestion and contributes to the synthesis of vitamins B and K.

Classification of Organisms

Taxonomy

Taxonomy is the science of classifying organisms based on their natural relationships.
Scientists observe the characteristics of organisms to classify them into various groups.
Organisms with similar traits are placed in the same group.

Carl Woese introduced a classification system based on molecular and cellular characteristics, dividing organisms into three domains:

Eubacteria (True bacteria)
Eukarya (All organisms with complex cells)
Archaea (Ancient bacteria)

Bacteria

General Characteristics of Bacteria

Bacteria are microscopic, unicellular organisms without a true nucleus (prokaryotic).
They have unique cell walls, reproduce through binary fission, and thrive in diverse environments.
Size: The smallest bacterium (Mycoplasma) measures around 0.3 μm in diameter, while Escherichia coli is 1.1 to 1.5 μm wide and 2.0 to 6.0 μm long.

Classification of Bacteria

Bacteria are classified based on the following characteristics:

1. Gram Reaction
   Gram-positive (+ve)
   Gram-negative (-ve)

2. Shape
   Cocci: Round or oval cells
   Bacilli: Rod-shaped cells
   Spirilla: Spiral-shaped bacteria
   Vibrio: Curved or comma-shaped rods
   Spirochetes: Slender, flexible spiral forms

3. Atmospheric Requirements
   Obligate Aerobes: Require oxygen to survive
   Obligate Anaerobes: Survive in oxygen-free environments
   Facultative Anaerobes: Can survive with or without oxygen
   Capnophiles: Thrive in high carbon dioxide levels

4. Endospore Formation
   Some bacteria form endospores to survive unfavorable conditions.
   Example: Bacillus and Clostridium species.

Bacterial Motility

Many bacteria move using flagella, which are thread-like locomotor appendages.
Flagella rotate to enable the bacteria to swim, with speeds ranging from 20 to 90 μm/second.

Types of Flagella

Monotrichous: A single flagellum at one end.
Amphitrichous: A flagellum on both ends.
Lophotrichous: Multiple flagella at one or both ends.
Peritrichous: Flagella distributed all over the bacterial surface.

Endospores

Endospores are resistant, dormant structures formed by certain bacteria to withstand harsh conditions.
They are characterized by extreme resistance to heat, radiation, and disinfectants.

Example: Bacillus and Clostridium species produce endospores.

Sporulation Process

DNA replication and axial filament formation.
Formation of a forespore.
Engulfment of the forespore by the parent cell.
Cortex formation with calcium and dipicolinic acid.
Formation of protein coats.
Maturation of the endospore.

Viruses

General Characteristics of Viruses

Viruses are intracellular parasites that require host cells to replicate.
They are non-living outside a host and can infect animals, plants, and even bacteria.
Viruses are made up of genetic material (DNA or RNA) surrounded by a protein coat called a capsid.

Virus Multiplication

The stages of virus multiplication include:

Absorption - Virus attaches to the host cell.
Penetration - Virus enters the cell.
Uncoating - Viral genome is released.
Replication - Viral components are synthesized.
Assembly - New virus particles are assembled.
Release - Viruses are released to infect new cells.

Fungi

General Characteristics of Fungi

Fungi are eukaryotic microorganisms with cell walls rich in chitin.
They reproduce asexually through spores and are classified into molds, yeasts, and dermatophytes.
Fungi play a vital role in decomposition and nutrient cycling.

Types of Fungi

Molds - Filamentous fungi that grow in long, branching structures.
Yeasts - Single-celled fungi that reproduce by budding.
Dermatophytes - Cause skin, hair, and nail infections.

Parasites

General Characteristics of Parasites

Parasites are organisms that live on or inside a host and derive nutrients at the host's expense.
They include protozoa, helminths, and arthropods.

Protozoa

Protozoa are unicellular, eukaryotic microorganisms.
They reproduce through asexual (binary or multiple fission) or sexual means.
They are classified into four groups based on their mode of movement:

Sporozoa (e.g., Plasmodium)
 Flagellates (e.g., Trypanosoma)
 Amoeboid (e.g., Entamoeba histolytica)
 Ciliates (e.g., Balantidium coli)