Bacterial Cell Structure

Bacterial Cell Structure

• Cell Wall: Rigid layer outside the cell membrane, composed of peptidoglycan (also known as murein)
  • Provides shape, support, and protection
• Cell Membrane: Semi-permeable membrane that regulates the flow of substances in and out of the cell
  • Composed of phospholipid bilayer with embedded proteins
• Cytoplasm: Jelly-like substance inside the cell membrane, where metabolic reactions occur
  • Contains ribosomes, DNA, and various organelles
• Flagella: Long, whip-like structures used for movement
  • Located outside the cell wall and cell membrane
• Pili: Short, hair-like structures used for attachment and DNA transfer
  • Located outside the cell wall and cell membrane

Metabolism

• Energy Sources: Bacteria can use various energy sources, including:
  • Light (phototrophy)
  • Chemical compounds (chemotrophy)
  • Organic compounds (organotrophy)
• Carbon Sources: Bacteria can use various carbon sources, including:
  • Organic compounds (heterotrophy)
  • Carbon dioxide (autotrophy)
• Metabolic Pathways: Bacteria use various metabolic pathways, including:
  • Glycolysis
  • Pentose phosphate pathway
  • Citric acid cycle
  • Electron transport chain

Gram Positive Species

• Cell Wall Characteristics:
  • Thick peptidoglycan layer (up to 40 layers)
  • Teichoic acids and lipoteichoic acids present
• Staining Characteristics: Retain crystal violet dye during Gram staining
• Examples:
  • Staphylococcus aureus
  • Bacillus subtilis
  • Clostridium difficile

Gram Negative Species

• Cell Wall Characteristics:
  • Thin peptidoglycan layer (1-2 layers)
  • Outer membrane present, containing lipopolysaccharides
• Staining Characteristics: Do not retain crystal violet dye during Gram staining
• Examples:
  • Escherichia coli
  • Pseudomonas aeruginosa
  • Salmonella enterica

Bacterial Cell Structure

• Cell Wall: Composed of peptidoglycan (murein), providing shape, support, and protection to the cell.
• Cell Membrane: Semi-permeable, composed of phospholipid bilayer with embedded proteins, regulating the flow of substances in and out of the cell.
• Cytoplasm: Jelly-like substance containing ribosomes, DNA, and various organelles, where metabolic reactions occur.
• Flagella: Long, whip-like structures used for movement, located outside the cell wall and cell membrane.
• Pili: Short, hair-like structures used for attachment and DNA transfer, located outside the cell wall and cell membrane.

Metabolism

• Energy Sources: Bacteria can use light, chemical compounds, and organic compounds as energy sources.
• Carbon Sources: Bacteria can use organic compounds and carbon dioxide as carbon sources.
• Metabolic Pathways: Bacteria use glycolysis, pentose phosphate pathway, citric acid cycle, and electron transport chain for metabolism.

Gram Positive Species

• Characteristics: Thick peptidoglycan layer (up to 40 layers), teichoic acids and lipoteichoic acids present in the cell wall.
• Staining: Retain crystal violet dye during Gram staining.
• Examples: Staphylococcus aureus, Bacillus subtilis, and Clostridium difficile are Gram positive species.

Gram Negative Species

• Characteristics: Thin peptidoglycan layer (1-2 layers), outer membrane present with lipopolysaccharides.
• Staining: Do not retain crystal violet dye during Gram staining.
• Examples: Escherichia coli, Pseudomonas aeruginosa, and Salmonella enterica are Gram negative species.

Characteristics

• Staphylococcus: Gram-positive, spherical bacteria that are 0.5-1.5 μm in diameter and can grow in clusters or singly
• Staphylococcus: Catalase-positive, which distinguishes them from Streptococcus, and can produce a variety of enzymes and toxins
• Streptococcus: Gram-positive, spherical bacteria that are 0.5-1.0 μm in diameter and can grow in chains or pairs
• Streptococcus: Catalase-negative

Laboratory Diagnosis

• Staphylococcus: Cultured on blood agar, producing a golden-yellow pigment, and can be differentiated from other species using mannitol salt agar
• Staphylococcus: Coagulase testing can identify S.aureus
• Streptococcus: Cultured on blood agar, producing a clear or greenish zone, and can be identified using bacitracin sensitivity testing and Lancefield grouping

Antibiotic Resistance

• Staphylococcus: Methicillin-resistant S.aureus (MRSA) is a significant concern, with resistance to beta-lactam antibiotics, such as penicillin and ampicillin
• Staphylococcus: Vancomycin-resistant S.aureus (VRSA) has also been reported
• Streptococcus: Resistance to macrolides, such as erythromycin and azithromycin, and decreased susceptibility to penicillin and other beta-lactam antibiotics
• Streptococcus: Resistance to fluoroquinolones, such as ciprofloxacin and levofloxacin

Identification

• Staphylococcus: Identified by Gram stain, morphology, and biochemical tests, with species-specific identification using PCR, DNA-DNA hybridization, or MALDI-TOF
• Streptococcus: Identified by Gram stain, morphology, and biochemical tests, with Lancefield grouping and PCR for specific streptococcal groups

Gram Positive and Gram Negative Species

• Gram-positive species include Staphylococcus aureus, S.epidermidis, S.saprophyticus, Streptococcus pyogenes, S.agalactiae, and S.pneumoniae
• Both Staphylococcus and Streptococcus are gram-positive bacteria, with no gram-negative species