General Bacteriology Overview

General Bacteriology

• Microbiology is the study of small living organisms like bacteria, fungi, and viruses.
• Organisms are classified into prokaryotes (bacteria, rickettsia, chlamydia) and eukaryotes (fungi, protozoa, plant and animal cells). Viruses are also separate.

Bacterial Structure

• Bacteria have a capsule, cell wall, plasma membrane, nucleoid, cytoplasm, and ribosomes.

Comparing Prokaryotes and Eukaryotes

• Prokaryotes lack a nuclear membrane and nucleolus, while eukaryotes do not.
• Prokaryotic chromosomes are single and circular, while eukaryotic ones are multiple and linear.
• Prokaryotes do not have membrane-bound organelles (like mitochondria or Golgi), whereas eukaryotes do.
• Prokaryotic cell walls contain peptidoglycan (mostly). Plant also have cell wall, but composed of cellulose. Animal cells do not have cell wall.
• Bacteria ribosomes are 70S (30S and 50S subunits), eukaryotic ones are 80S (40S and 60S subunits).
• Prokaryotes reproduce via binary fission, eukaryotes do so through mitosis or budding.

Classification of Bacteria

• Bacteria are classified based on shape (coccus, bacillus, spirillum, spirochaete), arrangement (diplococci, streptococci, staphylococci), and staining characteristics (gram-positive and gram-negative).

Bacterial Cell Structure

• Essential components: cell wall, cytoplasmic membrane, protoplasm (cytoplasm + nuclear material).
• Accessory components: capsule and slime, fimbriae (pili), flagella, spores, plasmids.
• These accessory structural components enhance pathogenicity, meaning it increases the ability of the bacteria to cause disease.

Cell Wall

• Rigid structure maintaining bacterial shape and providing protection against osmotic lysis (especially in hypotonic solutions).
• Gram-positive cell walls are thick and contain peptidoglycans and teichoic acids, while gram-negative ones are thin, containing peptidoglycan and an outer membrane with lipopolysaccharides (LPS).
• LPS is an endotoxin highly toxic and can cause inflammation, fever, and shock.
• The cell wall is important for classification and a good target for antibiotics like penicillin and cephalosporins (inhibiting cell wall synthesis).

Cytoplasmic Membrane

• Structure: a semipermeable membrane around the cytoplasm maintaining a constant internal environment.
• Functions: selective permeability (active and passive transport), excretion of hydrolytic enzymes and toxins, respiration and ATP production, DNA replication, and cell wall biosynthesis.

Mesosomes

• Invaginations of the cytoplasmic membrane.
• Functions in respiration (contain respiratory enzymes) and cell division (forming septum).

Cytoplasm

• Viscous, watery substance containing various components, including cytoplasmic inclusion granules (e.g., meta-polyphosphate) and ribosomes.
• Ribosomes are sites of protein synthesis (70S in size).

Bacterial Nucleus

• Single, circular DNA molecule (supercoiled).
• Multiplication occurs via binary fission (separation of copies).

Capsule and Slime

• External layers (glycocalyx) surrounding the cell wall.
• Capsules are firmly attached and dense, while slime layers are loosely attached.
• Composition varies (polysaccharides, polypeptides, hyaluronic acid).
• Protects against phagocytosis, aids in attachment to surfaces (forming biofilms), and contributes to virulence.

Flagella

• Long, thin appendages extending from the cell surface.
• Composed of flagellin protein.
• Involved in bacterial motility and chemotaxis, enabling movement toward favorable conditions and away from harmful ones.
• Different arrangements (polar, lophotrichous, peritrichous).

Pili/Fimbriae

• Short, hair-like appendages.
• Composed of pilin protein.
• Primarily involved in adhesion to host cells for colonization, therefore enhance pathogenicity.
• Two types (ordinary pili and sex pili).

Spores

• Highly resistant, dormant structures produced by some bacteria (Gram-positive).
• Formed in adverse conditions (e.g., nutrient depletion, dryness).
• Resistant to heat, chemicals, and UV radiation due to specific structures (layers, calcium dipicolinate).
• Not actively multiplying, but can germinate to active vegetative cells when conditions improve.
• Importance for survival and disease transmission.

Plasmids

• Extrachromosomal, circular DNA molecules.
• Replicate independently of the bacterial chromosome. - Diverse functions, including:
• resistance to antibiotics (R-plasmids), toxins (virulence plasmids), conjugation, and genes for enzymes involved in nutrient utilization.

Explore the fascinating world of general bacteriology, where you'll learn about the classification of microorganisms, the structure of bacteria, and the key differences between prokaryotes and eukaryotes. This quiz will deepen your understanding of microbial life and its unique characteristics.