Microorganisms and Bacteria Quiz

Microorganisms

• Microorganisms are living organisms too small to be seen with the naked eye.
• They can be classified as cellular or acellular.
• Cellular organisms are made up of one cell, while acellular organisms are not.

Bacteria

• Bacteria are unicellular prokaryotic organisms.
• Prokaryotic organisms contain a primitive nucleus.
• Bacteria are approximately 1 micrometer in diameter.
• They contain both DNA and RNA.
• Bacteria can grow on ordinary media.
• They reproduce through binary fission.
• Bacteria can be observed using a light microscope.
• They are sensitive to antibacterial agents.

Viruses

• Viruses are acellular microorganisms.
• They do not have a cell structure.
• Viruses are one of the smallest infectious agents.
• They are obligate intracellular parasites, meaning they rely on the biological machinery of a host cell for survival and reproduction.

Bacterial Morphology

• Bacteria vary in size, shape, and arrangement.

Bacterial Size

• Bacteria are small, but their size can vary.
• 1 micrometer (µm) is equal to 10^-3 millimeters.

Bacterial Shapes

• Coccus: Spherical or ovoid shaped.
• Bacillus: Rod-like shaped.
• Spiral: Spirilla or spirochetes (spiral shaped).

Bacterial Arrangement

• Bacteria of the same shape can be arranged in different ways.
• Arrangement can be in pairs, chains, clusters, or other groupings.
• Arrangement helps differentiate and name bacteria.

Staining of Bacteria

• Bacteria cells are nearly colorless and transparent.
• Staining techniques are used to color them.
• Staining methods can be used to determine bacterial shape and size under a microscope.

Types of Stains

• Simple stain: Uses a single basic dye, e.g. methylene blue. All bacteria take on the color of the dye.
• Differential stain: Uses two dyes separated by a decolorizing agent, e.g. Gram stain and Ziehl-Neelsen stain.
• Special stain: Used to stain specific structures, e.g. inclusion granules (carbohydrates, lipids).

Bacterial Ultrastructure

• Bacteria have a number of internal structures.

Cytoplasm

• The cytoplasm contains the following:
  • Nucleoid: The genetic material of the bacteria (DNA).
  • Plasmids: Small, circular DNA molecules.
  • Ribosomes: Sites of protein synthesis.
  • Inclusion granules: Storage granules for nutrients.

Cytoplasmic Membrane

• The phospholipid protein bilayer that surrounds the cytoplasm.
• It lacks sterols.

Functions of the Cytoplasmic membrane

• Selective transport: Controls the movement of substances into and out of the cell. This can occur through:
  • Simple diffusion
  • Facilitated diffusion
  • Active transport
• Mesosomes: Complex invaginations of the cytoplasmic membrane. They are involved in cell division and sporulation.

Cell Wall

• Surrounds the cytoplasmic membrane.
• The cell wall is strong and rigid, but has some elasticity.

Structure of the Cell Wall

• Peptidoglycan is the major component that gives the cell wall its strength.

Peptidoglycan

• Gram-positive bacteria: Have 40 sheets of peptidoglycan, making up 50% of their cell wall material.
• Gram-negative bacteria: Have 1-2 sheets of peptidoglycan, making up 5-10% of their cell wall material.

Gram-positive Cell Wall

• Composed of:
  • Peptidoglycan
  • Teichoic acids

Gram-negative Cell Wall

• Composed of:
  • Peptidoglycan
  • Outer membrane: A phospholipid protein bilayer outside of the peptidoglycan layer. Its outer surface is made up of lipopolysaccharide (LPS).
  • Periplasmic space: The space between the cytoplasmic and outer membranes.

Functions of the Cell Wall

• Maintains the bacterium's characteristic shape.
• Supports the cytoplasmic membrane against internal osmotic pressure.
• Plays a role in cell division.
• Responsible for the staining affinity of the bacteria.

Mycoplasma

• The only group of bacteria that naturally lacks a cell wall.
• Mycoplasmas do not have a defined shape due to the absence of a rigid cell wall.
• They are resistant to cell wall inhibitors like penicillins and cephalosporins.

L-forms

• Bacteria that normally have a cell wall can develop L-forms when exposed to lysozyme (an enzyme that breaks down peptidoglycan) or antibiotics that block peptidoglycan biosynthesis. This occurs if the bacteria are in an isotonic medium.
• L-forms can resynthesize their cell walls when the inducing stimulus is removed.
• L-forms may survive antibiotic therapy.
• Their reversal to the walled state can cause relapses of infection.

Capsule and Glycocalyx

• Some bacteria produce large amounts of extracellular polysaccharides outside their cell wall, forming an additional surface layer.
• Capsule: Adheres tightly to the surface of the cell.
• Glycocalyx: A loose meshwork of polysaccharide fibrils extending out from the cell.

Functions of Capsule and Glycocalyx

• Protects the cell wall from antibacterial agents.
• Protects the bacterial cell from phagocytosis (engulfment by immune cells).
• Aids in bacterial attachment to surfaces, facilitating infection.

Flagella

• Long, whip-like appendages found in many bacterial genera.
• Can only be seen using an electron microscope.

Functions of Flagella

• Responsible for bacterial motility.
• Allow bacteria to move towards attractants (e.g. nutrients) or away from repellants (e.g. disinfectants), a process called chemotaxis.

Pili (Fimbriae)

• Shorter and thinner than flagella.
• Found in many bacterial genera.
• Can only be seen using an electron microscope.

Functions of Pili (Fimbriae)

• Adherence: Contribute to bacterial attachment to host cells, establishing infection.
• Conjugation: Form an attachment tube (sex pilus) between two bacterial cells, allowing for the transfer of DNA.

Bacterial Spores (Endospores)

• Highly resistant resting phase formed by some bacteria (e.g. Bacillus and Clostridium).
• Spores do not grow or reproduce.
• They are formed in-vitro (in lab conditions) under unfavorable conditions.

Sporulation

• Triggered by unfavorable environmental conditions, including:
  • Nutrient depletion
  • Accumulation of metabolites
  • Changes in growth requirements

Viability and Resistance of Bacterial Spores

• Spores are highly resistant to disinfectants, dryness, and heat.
• They can withstand moist heat at 121°C for 10-20 minutes.

Germination

• Endospores can quickly return to the vegetative state (active growth and reproduction) in response to environmental changes, usually within 15 minutes.

Staining of Bacterial Spores

• Gram's stain does not stain bacterial spores.
• They require special stains.

Bacterial Growth and Physiology

• Bacterial growth refers to an increase in the size and number of bacterial cells.

Bacterial Reproduction

• Bacteria reproduce through binary fission.

Generation Time (Doubling Time)

• The time it takes for a bacterial cell to divide and produce two daughter cells.
• Can be as short as 13 minutes or as long as 24 hours.

Growth Requirements

• Factors necessary for bacterial growth.

Moisture

• An absolute requirement for bacterial growth.

Nutrients

• Bacteria can be classified based on their nutrient source:
  • Autotrophs: Can use simple inorganic materials as a source of carbon and synthesize complex organic substances from them.
  • Heterotrophs: Require organic sources of carbon, as they cannot synthesize complex organic substances from simple inorganic materials.
• Most bacteria of medical importance are heterotrophic.

Oxygen (O2)

• Bacteria require certain enzymes for aerobic respiration (growth in the presence of oxygen):
  • Superoxide dismutase enzyme: Detoxifies superoxide (O2-) radicals.
  • Catalase enzyme: Detoxifies hydrogen peroxide (H2O2).

Oxygen Requirements

• Strict aerobes: Require oxygen for growth.
• Facultative anaerobes: Use oxygen when present, but can continue to grow in the absence of oxygen.
• Strict anaerobes: Require the complete absence of oxygen to grow because they lack superoxide dismutase and catalase enzymes. They are killed by oxygen.

Carbon Dioxide (CO2)

• Most bacteria need only the minute amount of CO2 present in the air to grow.
• Some species require higher concentrations (5-10%) of CO2.

Temperature and pH

• The optimal growing temperature for most bacteria is 37°C (body temperature).
• The optimal pH for most bacteria is 7.2-7.6.

Bacterial Growth Curve

• Lag phase: Constant number of viable organisms; bacteria are adapting to the new environment, forming new enzymes, and preparing for growth.
• Exponential (logarithmic) phase: Marked increase in the number of organisms; growth rate is accelerating, giving a linear plot on logarithmic scale.
• Stationary phase: Constant number of organisms at a high level; growth rate is balanced by death rate due to nutrient depletion and accumulation of toxic products.
• Decline phase: Markedly reduced number of organisms; death rate exceeds the multiplication rate due to nutrient exhaustion and accumulation of toxic products.

Test your knowledge on microorganisms, focusing on bacteria, their characteristics, and classification. This quiz covers essential aspects of cellular and acellular organisms, along with bacterial morphology, size, and reproduction methods. Perfect for biology students and enthusiasts!