MICP

• Bacteria are prokaryotic organisms with simpler structures (unicellular)
• Bacteria can be classified into three basic shapes determined by the cell wall:

  • Cocci: spherical or round shaped organisms
  • Bacilli: rod-shaped organisms
  • Coccobacilli: some may be very short, resembling elongated cocci
  • Curved and spiral-shaped bacteria show many variations in their morphology
• Bacteria size ranges from 0.2 to 5 micrometers

  • The smallest bacteria is Mycoplasma, which is the same size as the largest viruses
• Envelope Structures protect bacteria from harsh environmental conditions
• Glycocalyx (Sugar coat) is a gelatinous substance located external to the cell wall, composed of polysaccharide or polypeptide or both

  • Capsule is strongly attached to the cell wall, determined by negative staining
  • Slime layer is loosely attached to the cell wall
• Cell wall, sometimes called murein sacculus:

  • Multi-layered in gram-positive bacteria
  • Single-layered in gram-negative bacteria
• Special Components of Gram-Positive Cell Walls:

  • Teichoic acids comprise major surface antigens, can elicit an antibody response
  • Lipoteichoic Acid is linked to the peptidoglycan layer
  • Wall Teichoic Acid is linked to the peptidoglycan layer only
  • Polysaccharides include neutral and acidic sugars
  • Periplasmic space contains granular layer with lipoteichoic acid
• Special Components of Gram-Negative Cell Walls:

  • Outer Membrane is a bilayer structure with lipopolysaccharides
  • Porins allow the passage of small hydrophilic substances
  • Lipid A is responsible for endotoxin activity
  • O Antigen is a repeat unit unique in every species of bacteria
  • Lipoprotein anchors the outer membrane to the peptidoglycan layer
  • Periplasmic Space is a fluid-filled space between the outer and inner plasma membrane
• Acid Fast Cell Wall:

  • Possesses an outer layer that is lipid-rich
  • Mycolic acids composed of large amounts of waxes
  • Acid-fast organisms cannot be stained using the reagents for gram staining
  • Mycolic acid forms a layer outside the thin layer of peptidoglycan
  • Can be stained by carbol fuchsin dye
• Projecting Structures: Flagella are made up entirely of flagellin molecules

  • Flagella are classified into four types: Monotrichous, Lophotrichous, Amphitrichous, Peritrichous, Atrichous
  • Flagella have a long outermost region (filament) and a basal body that anchors them to the cell wall and plasma membrane
• Projecting Structures: Pili or Fimbriae function for motility

  • Pillins are structural protein subunits
  • Common pili function for adherence to the cell surface
  • Sex pili (conjugation) attach to another bacterium during bacterial gene transfer
• Projecting Structures: Axial Filaments, also called endoflagella, found in spirochetes

  • Composed of bundles of fibrils that spiral around the cell
  • Propels spirochetes in a spiral motion (corkscrew motion)
• Cytoplasmic Membrane, also called cell membrane or plasma membrane, is located beneath the cell wall

  • Selectively permeable membrane that allows transport
  • Site of ATP production and contains enzymes for biosynthesis
• Internal Structures:

  • Nucleoid contains a single circular double-stranded DNA
  • Mesosomes function for cell division
  • Ribosomes function for protein synthesis
  • Granular or inclusion bodies serve for storage of food and energy
  • Endospores composed of dipicolinic acid enable bacteria to withstand adverse environmental conditions
• Bacterial Growth Requirements:

  • Growth involves an increase in the sum of all components of the organism
  • Microbial growth is concerned with the increase in the number of cells
  • Bacterial colonies are composed of thousands of cells
  • Requirements for microbial growth include physical aspects (temperature, pH, osmotic pressure) and chemical requirements (carbon, nitrogen, sulfur, phosphorus, oxygen, trace elements, organic growth factors)
• Nutritional Requirements:

  • Carbon is the structural backbone of organic molecules
  • Microorganisms may be classified into Autotrophs (lithotrophs) and Heterotrophs (organotrophs) based on their carbon source
  • Nitrogen, sulfur, and phosphorus are necessary for the synthesis of cellular materials such as proteins and nucleic acids
  • Inorganic ions like magnesium, potassium, calcium, iron, and trace elements are essential for various cellular functions
• Physical Requirements:

  • Water/moisture serves as the medium for nutrient acquisition
  • Oxygen is used by aerobic bacteria for cellular respiration
  • Microorganisms are classified as aerobes or anaerobes based on their oxygen requirements
• Microorganisms are classified as either aerobes or anaerobes based on their oxygen requirements
• Aerobes utilize molecular oxygen for energy production
• Obligate anaerobes cannot survive in the presence of oxygen
• Facultative organisms can grow and survive under both aerobic and anaerobic conditions
• Some organisms are microaerophiles, able to grow at low oxygen tension with diminished growth rate
• Capnophiles require the addition of carbon dioxide to enhance their growth
• Microbes are classified into three groups based on their temperature requirements
• Thermophiles grow best at temperatures higher than 40 °C
• Mesophiles require an optimal temperature of 20-40 °C
• Psychrophiles require an optimum temperature of 10-20 °C
• Most medically important bacteria are mesophiles
• pH is another requirement for bacteria, with different classifications based on acidity or alkalinity
• Alkalophiles grow best in pH 8.4-9.0
• Neutrophiles grow best in pH 6.5-7.5, with most medically important bacteria being neutrophiles
• Some bacteria require a pH less than 6.0 and are called acidophiles
• Most organisms grow best under ideal osmotic pressure conditions
• Normal microbial cytoplasmic salt concentration is approximately 1%
• Halophiles require high salt concentrations for growth
• Osmophiles require high osmotic pressure for optimal growth
• Bacterial Growth Curve consists of four phases
• Lag Phase: period of adjustment for bacteria in a new environment with no increase in microorganisms
• Log Phase: rapid cell division and exponential growth
• Stationary Phase: period of equilibrium with slowed growth and nutrient depletion