Bacterial Morphology and Envelopes

Bacterial Morphology

• Fundamental bacterial shapes include coccus, bacillus, and spirilla.
• Coccus (cocci) bacteria are spherical, oval, or round-shaped.
• Diplococcic bacteria occur in pairs.
• Streptococci bacteria occur in chains.
• Staphylococci bacteria occur in clusters.
• Tetrad bacteria occur in groups of four.
• Octad bacteria occur in groups of eight.
• Bacillus (bacilli) bacteria are rod-shaped, examples includes E.coli and Salmonella.
• Spirilla bacteria are spiral-shaped, for example Treponema pallidum.

Envelope Structures

• Glycocalyx is the outermost covering of some bacteria, a gelatinous substance and referred to as a capsule.
• The capsule is indicative of the virulence, or degree of pathogenicity.
• The outer membrane of gram-negative bacteria is composed of LPS (lipopolysaccharide).
• A lipid portion in LPS (Lipid A) is responsible for endotoxin production.
• The cell wall's principal component is peptidoglycan, also known as "Murein Sacculus."
• The cell wall provides rigid support and shape.
• The Periplasmic Space is a fluid-filled space containing enzymes which breakdown large molecules.
• The Periplasmic Space has transport proteins for regulating cell osmolality.
• The cytoplasmic membrane, also known as the plasma membrane or cell membrane, is beneath the cell wall.
• The cytoplasmic membrane encloses the cytoplasm, sometimes called a "CELL SACK."
• Carries enzymes on its surface.
• Involved in selective permeability.
• The cytoplasmic membrane allows the active transport of molecules in and out of the bacterial cell.

Projecting Structures

• Pilus or Fimbria are thread-like structures which project from the capsule.
• Pilus are used for adherence to cell surface.
• Pili facilitate attachment during conjugation (sex pilus).
• Pili are commonly seen in gram-negative organisms.
• Axial Filaments and Flagella are whip-like structures and organs for motility.
• Monotrichus refers to a single polar flagellum.
• Lophotrichous refers to a tuft of flagella at one end of a bacterium.
• Amphitrichous refers to flagella at both ends of the bacterium.
• Peritrichous refers to flagella all around the bacillus.
• Atrichous refers to bacteria without flagellum.

Internal Structures

• Nucleoid does not contain a nucleoplasm/nuclear membrane.
• The Nucleoid contains genetic material (DNA).
• Mesosome is required for cell division.
• Mesosome is involved in secretion of substances.
• Ribosomes are sites for protein synthesis.
• Ribosomes are targets for the action of antibiotics.
• Endospores contain dipicolinic acid.
• Endospores are resistant to heat, drying, chemical agents, and radiation.
• Endospores are difficult to destroy.

Bacterial Growth Requirements

• Carbon makes up the structure backbone (skeleton).
• Autotrophs (lithotrophs) use inorganic salts and water as their carbon source.
• Photolithotrophs derive their energy from light.
• Chemolithotrophs derive their energy from oxidation of inorganic substances.
• Heterotrophs (organotrophs) utilize organic substances like sugars or glucose.
• Photoorganotrophs derive their energy from light.
• Chemoorganotrophs derive their energy from oxidation.
• Nitrogen, sulfur, and phosphorus are necessary for synthesis of cellular materials, including proteins and nucleic acids.
• Magnesium stabilizes ribosomes, cell membranes, and nucleic acids.
• Potassium is required for normal functioning and integrity of ribosomes.
• Calcium is an important constituent of the cell wall and contributes to its resistance.
• Iron is part of cytochrome and functions as a cofactor in enzymatic activities.
• The bacterial cell is mainly composed of water.
• Aerobes utilize molecular oxygen for energy.
• Strict aerobes strictly require oxygen for growth.
• Obligate/strict anaerobes cannot survive in the presence of oxygen.
• Aerotolerant anaerobes can resist exposure to oxygen and are not killed by its presence.
• Microaerophilic anaerobes can grow at low oxygen tension.
• Thermophiles are heat-loving bacteria which grow in temperatures of 50-60°C.
• Mesophiles have an optimum growth temperature of 20-40°C.
• Common medically important bacteria are mesophiles.
• Psychrophiles grow at -10-20°C.
• Alkalophiles prefer pH 8.4-9.0.
• Neutrophiles prefer pH 7.5-8.0.
• Acidophiles prefer pH 6.5-7.0.
• Halophiles grow in high salt concentrations.
• Osmophiles grow in high osmotic pressure.

Bacterial Growth Curve

• Lag phase involves adjustment for the bacteria in a new environment,DNA & enzymes synthesis and increase in size not number.
• Logarithmic/Exponential/Log phase show rapid cell division, an increase in number, and cells which are metabolically active.
• The generation time of bacteria can be determined during the Log phase.
• Stationary Phase shows a period of equilibrium, a slowing of the growth rate, nutrients are depleted, and toxic waste accumulates.
• Death/decline phase is characterized by rapid cell death.