microscopy - chapter 4

CELL STRUCTURES

• Characteristics of Bacteria

  • Bacteria are unicellular organisms with diverse shapes and arrangements.

  • They possess cell walls, cytoplasmic membranes, and various organelles depending on type.

SPONTANEOUS GENERATION & BIOGENESIS

• Spontaneous Generation

  • Definition: Belief that life arises from non-living matter.

  • Discredited by Francesco Redi in 1668 through his experiment with rotting meat and flies.

  • Louis Pasteur further disproved this theory, proving contamination from air contains microorganisms.

• Biogenesis

  • Definition: Life arises from pre-existing living matter.

  • Established as the principle guiding microbiology.

  • Louis Pasteur is known as the father of microbiology due to his contributions.

GERM THEORY

• Louis Pasteur and Germ Theory

  • Conducted significant experiments linking specific microorganisms to diseases.

  • Suggested boric acid to kill microorganisms in clinical settings.

  • Germ Theory indicates that many diseases are caused by specific microbes.

• Joseph Lister

  • Known as the "Father of Antiseptic Surgery" for promoting antiseptic techniques.

  • Introduced carbolic acid to sterilize surgical instruments, significantly reducing surgical deaths.

CELL THEORY

• Robert Hooke

  • Examined cork and discovered cells, coining the term "cells" to describe the compartmental structure.

  • Cell Theory states:

    1. All living things are composed of cells.

    2. The cell is the basic unit of life.

    3. All cells arise from pre-existing cells.

MICROSCOPY

• Types of Microscopes

  • Basic microscopes first observed microorganisms; modern compound microscopes utilize multiple lenses for magnification.

STAINING TECHNIQUES

• Wet Mounts

  • Utilized for observing living organisms' motility.

  • Example: Trichomonas.

• Simple Stains

  • Uses basic dyes to stain cellular components (e.g., methylene blue, crystal violet).

• Differential Stains

  • Gram Stain

    • Divides bacteria into gram-positive and gram-negative based on cell wall structure.

    • Improper decolorization can affect results.

  • Acid-Fast Stain

    • Identifies bacteria with high waxy content in cell walls, such as Mycobacterium.

    • Uses carbol fuchsin and methylene blue for staining structure.

SPECIAL STAINS

• Capsule Stain

  • Highlights gelatinous layers around microbes that contribute to virulence.

• Endospore Stain

  • Stains resistant endospores found in genera like Bacillus and Clostridium.

• Flagella Stain

  • Visualizes flagella, thin appendages aiding in bacterial motility.

FLUORESCENT DYES & IMMUNOFLUORESCENCE

• Used to label cellular components and count microbial cells.

• Distinguishes living and dead cells by binding cellular structures.

• Immunofluorescence utilizes tagged antibodies for specific protein detection.

BACTERIAL MORPHOLOGY

• Shapes and Arrangements

  • Bacteria may be spherical (cocci), rod-shaped (bacilli), or spiral. Their arrangements can suggest specific bacterial types.

  • Examples:

    • Diplococci: Pairs (e.g., Streptococcus pneumoniae).

    • Bacilli: Chains (e.g., Bacillus anthracis).

    • Spirals: Various forms (e.g., Helicobacter pylori).

PROKARYOTIC CELL STRUCTURE

• Importance of Structure

  • Structure is crucial for antibiotic targeting.

• Cytoplasmic Membrane

  • Acts as a gatekeeper for cellular material.

• Cell Envelope

  • Composed of cell wall, cytoplasmic membrane, and capsule (if present).

• Cytoplasm

  • Contains ribosomes, nutrients, and a nucleoid region housing the chromosome.