Bacterial Classification Types

Bacterial Classification

• Based on cell wall composition:
  • Gram-positive bacteria: thick peptidoglycan layer, no outer membrane
  • Gram-negative bacteria: thin peptidoglycan layer, outer membrane with lipopolysaccharides
• Based on shape:
  • Spherical (cocci)
  • Rod-shaped (bacilli)
  • Spiral (spirilla)
  • Comma-shaped (vibrios)
• Based on metabolism:
  • Phototrophic: use light energy
  • Chemotrophic: use chemical energy
  • Heterotrophic: obtain energy by consuming other organisms
• Based on oxygen requirements:
  • Aerobic: require oxygen
  • Anaerobic: do not require oxygen
  • Facultative anaerobic: can grow with or without oxygen

Bacterial Structure

• Cell wall: provides shape, support, and protection
  • Peptidoglycan (murein): thick, rigid layer in Gram-positive bacteria
  • Outer membrane: thin, flexible layer in Gram-negative bacteria
• Cell membrane: regulates transport, maintains cell environment
  • Phospholipid bilayer with embedded proteins
• Cytoplasm: site of metabolic reactions
  • Gel-like substance with water, salts, and organic molecules
• Nucleoid: region with genetic material
  • No true nucleus, genetic material is not membrane-bound
• Ribosomes: site of protein synthesis
  • Small, spherical organelles found throughout cytoplasm
• Flagella: used for motility
  • Long, whip-like structures composed of protein
• Pili: used for adhesion and DNA transfer
  • Short, hair-like structures composed of protein
• Capsule: protective layer outside cell wall
  • Polysaccharide or protein layer that helps evade host immune system

Bacterial Classification

• Bacteria classified based on cell wall composition, shape, metabolism, and oxygen requirements
• Gram-positive bacteria: thick peptidoglycan layer, no outer membrane
• Gram-negative bacteria: thin peptidoglycan layer, outer membrane with lipopolysaccharides

Bacterial Shapes

• Spherical (cocci)
• Rod-shaped (bacilli)
• Spiral (spirilla)
• Comma-shaped (vibrios)

Bacterial Metabolism

• Phototrophic: use light energy
• Chemotrophic: use chemical energy
• Heterotrophic: obtain energy by consuming other organisms

Oxygen Requirements

• Aerobic: require oxygen
• Anaerobic: do not require oxygen
• Facultative anaerobic: can grow with or without oxygen

Bacterial Structure

Cell Wall

• Provides shape, support, and protection
• Peptidoglycan (murein): thick, rigid layer in Gram-positive bacteria
• Outer membrane: thin, flexible layer in Gram-negative bacteria

Cell Membrane

• Regulates transport, maintains cell environment
• Phospholipid bilayer with embedded proteins

Cytoplasm

• Site of metabolic reactions
• Gel-like substance with water, salts, and organic molecules

Nucleoid

• Region with genetic material
• No true nucleus, genetic material is not membrane-bound

Ribosomes

• Site of protein synthesis
• Small, spherical organelles found throughout cytoplasm

Flagella

• Used for motility
• Long, whip-like structures composed of protein

Pili

• Used for adhesion and DNA transfer
• Short, hair-like structures composed of protein

Capsule

• Protective layer outside cell wall
• Polysaccharide or protein layer that helps evade host immune system

Classification of Living Organisms

• All living beings can be classified into three kingdoms: Plant, Animal, and Protista.
• Microorganisms are a heterogeneous group of several distinct living structures of microscopic size, classified under the kingdom Protista.

Types of Microorganisms

• Prokaryotes: Bacteria and blue-green algae, unicellular, capable of performing essential life processes, lacking chlorophyll.
• Eukaryotes: Fungi, algae (except blue-green algae), protozoa, and slime moulds.
• Archaebacteria: Closely related to eukaryotes, do not include human pathogens.

Bacterial Classification

• Bacterial classification: arrangement of organisms into taxonomic groups based on phenotypic and genotypic similarities and differences.
• Three main approaches: phylogenetic, Adansonian, and genetic classifications.

Phylogenetic Classification

• Hierarchical classification representing a branching tree-like arrangement.
• Example: E. coli classification:
  • Division: Protophyta
  • Class: Schizomycetes
  • Order: Eubacteriales
  • Family: Enterobacteriaceae
  • Tribe: Escherichiae
  • Genus: Escherichia
  • Species: coli

Adansonian Classification

• Based on all characteristics expressed at the time of study, giving equal weight to all measurable features.

Genetic Classification

• Based on homology of DNA base sequences of microorganisms, using DNA hybridization or recombination methods.

Bacterial Anatomy

• Outermost layer consists of a rigid cell wall and cytoplasmic membrane.
• Protoplasm includes cytoplasm, cytoplasmic inclusions (ribosomes, mesosomes, granules, vacuoles, and nuclear body).
• Some bacteria have a viscid layer (slime layer or capsule) and filamentous appendages (flagella and fimbriae).

Slime Layer

• Structured paracrystalline protein layer composed of a single kind of protein molecule, sometimes with carbohydrates attached.
• Resistant to proteolytic enzymes and protein-denaturing agents, protects the cell from wall-degrading enzymes and bacteriophages.

Capsule

• Gelatinous secretion outside the cell wall.