What are Bacteria?

What are Bacteria?

• Microscopic, single-celled organisms with a diameter of 0.2-2 µm and a length of 1-10 µm
• Prokaryotic organisms with different shapes
• Lack membrane-bound organelles
• Can exist both inside and outside other organisms
• Can survive in extreme habitats, known as the "microbiome"

Microbiome

• Includes all microorganisms in a particular environment
• Encompasses the air microbiome, soil microbiome, water microbiome, and human body microbiome
• Airborne bacteria can be found in bioaerosol, droplets, dust, and particles
• Released from activities of animals, plants, and humans

Bacteria in Humans

• Play a vital role in digestion, immune system function, and overall health
• Beneficial bacteria aid in digestion and immune system function
• Harmless bacteria do not cause harm, while harmful bacteria can cause infections

Characteristics of Life

• Metabolism: convert nutrients into energy for growth and reproduction
• Reproduction: through binary fission
• Response to stimuli: change in pH, temperature, and nutrient scarcity
• Homeostasis: regulation of internal stability and balance
• Evolution: through mutation, gene transfer, and natural selection
• Genetic material: DNA

Fundamentals of Bacteria

• Cell structure: prokaryotic cell with no defined organelles and genetic material in the nucleoid zone
• Ecology and diversity: found everywhere on earth, exhibiting great diversity in morphology, physiology, and ecological role
• Pathogenicity: produce virulent toxins, colonize host tissue, avoid the immune system, and cause infection

Basic Characteristics of Bacteria

• Cell wall: distinct composition
• Cell membrane: extra layer
• Primitive cell structure: no distinct nucleus
• Cell organelles: simple organization
• Ribosome: 70 S type
• DNA gyrase: unique enzyme
• Respiration: aerobic without mitochondria
• Reproduction: multiple methods
• Pilli: sexual reproduction organelles
• Distribution: cosmopolitan, found everywhere
• Feeding dependence: many modes
• Chloroplast: absent

Bacteria Identification

• Based on biochemical tests, such as:
  • Catalase: detect hydrogen peroxide breakdown
  • Coagulase: detect blood clotting
  • Oxidase: detect cytochrome C that transfers electrons to oxygen
  • Tryptophanase: detect indole production
  • Sugar fermentation: detect fermentation ability to produce acid and gas

Classification of Bacteria

• Based on:
  • Shape
  • pH
  • Oxygen requirement
• Shapes:
  • Coccus: spherical or round
  • Bacillus: rod-shaped
  • Spiral: curve, spiral, or twisted
• Compound shapes:
  • Diplo-: divided cells remain in pairs
  • Strepto-: divided cells remain in chains
  • Tetrad-: divided cells remain in groups of four in two planes
  • Sarcinae: divided cells remain in groups of eight in three planes
  • Staphylo-: divided cells remain in clusters in multiple planes

Classification Based on pH

• Acidiphiles: pH ≤ 5, e.g., Acidithiobacillus
• Neutrophiles: pH 7, e.g., human pathogens and environmental microbes
• Alkaliphiles: pH > 9, e.g., Bacillus alkalophilus and B. firmus
• Neutrotolerant/Facultative: wide range of pH, e.g., gut bacterium (Escherichia coli)

Classification Based on Oxygen Requirement

• Aerobes: 21% oxygen, e.g., Bacillus, Pseudomonas, Micrococcus, and Staphylococcus
• Facultative anaerobes: grow in presence or absence of oxygen, e.g., Escherichia coli, Pseudomonas aeruginosa, Staphylococcus, Listeria, Salmonella, Shewanella oneidensis, and Yersinia pestis
• Anaerobes: grow in absence of oxygen, e.g., Bacilli, Lactobacilli, Bacteroides, Clostridium, and Staphylococcus
• Microaerophiles: grow in slightly reduced oxygen levels, e.g., Vibrio, Campylobacter, Legionella, Neisseria...