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• Microbiology: The study of microorganisms and immunology.
• Microorganisms: Small organisms not visible to the naked eye, examined using a microscope.
• Taxonomy: The science of naming microorganisms and grouping them.
• Taxonomic ranks: Used group microorganisms, often using genus and species.
• Microorganisms are grouped by similar properties and differentiated by specific characteristics.

Why Study Microbiology?

• Microorganisms cause diseases, necessitating study for treatment methods.
• Microorganisms are vital for maintaining nature's balance.
• Microorganisms are involved in human activities such as making yogurt and releasing antibiotics.
• Microorganisms can be used in experiments and produced in large quantities.

Microbes Causing Infections

• Bacteria (prokaryotic cells).
• Viruses (genetic material with a cover), not true cells, cannot function without invading a living cell.
• Fungi (eukaryotic cells).
• Parasites (studied in parasitology).

General Properties of Microorganisms

• Microorganisms cannot be seen by the naked eye; observation requires a microscope.
• Microorganisms are mostly unicellular.
• Microorganisms have a simple structure (compared to plants and animals).
• Microorgamisms have rapid adaptability.
• Microorganisms have a high rate of reproduction.
• Microorganisms possess rapid biochemical activity.
• Microorganisms have the capacity for self-sufficiency and reproduction.

Prokaryotic Cell vs. Eukaryotic Cell

• Prokaryotic Cells: Bacteria, Rickettsia, and Chlamydia.
• Eukaryotic Cells: Fungi and Protozoa.
• Cell Wall (Prokaryotic): Usually based on peptidoglycan.
• Cell Wall (Eukaryotic): Present, based on cellulose or chitin.
• Cytoplasm (Prokaryotic): Lacks membrane-bound organelles.
• Cytoplasm (Eukaryotic): Contains several membrane-bound organelles.
• Nucleus (Prokaryotic): Single chromosome (Haploid), no nucleoli, no nuclear membrane.
• Nucleus (Eukaryotic): More than one chromosome (Diploid), nucleoli present, nuclear membrane is present.
• Division (Prokaryotic): Simple binary fission (SBF).
• Division (Eukaryotic): Mitosis.
• Ribosome (Prokaryotic): Smaller (70S).
• Ribosome (Eukaryotic): Larger (80S).

Bacterial Distribution and Classification

• Bacteria are widely distributed in nature.
• Bacteria classification is based on habitat.
• Saprophytic Bacteria: Live on inanimate materials (like soil, water).
• Saprophytic Bacteria do not cause diseases.
• Man-Animal Symbiotic Bacteria: Live in humans and animals.
• Commensalism: One organism benefits, and the other is not affected, such as bacteria on skin.
• Under certain conditions, commensal bacteria can cause diseases and are termed opportunistic or potential pathogens
• In cases of weakened immune defenses or changes in the organism's natural habitat.
• For example, E. coli usually resides in the intestine without harm but can become pathogenic if it moves to the renal system.

Bacterial Infections

• Bacteria in the mouth can cause issues like heart valve problems if they enter the bloodstream during procedures, emphasizing the need for antibiotics in at-risk patients.

Mutualism in Bacteria

• Both organisms benefit, such as bacteria in the GIT that provide vitamins.
• Parasitism: One organism benefits at the expense of the other, causing harm.

Bacterial Harm

• Not all bacteria are harmful; some are useful or harmless.
• Bacteria can be used to produce antibiotics and fermented foods like yogurt.
• The morphology of bacteria varies in shape.

Bacterial Characteristics

• Size: Measured by microns.
• Shape:
  • Cocci (spherical).
  • Bacilli (rod-shaped).
  • Vibrio (comma-shaped).
  • Spirochete (spiral).
• Staining: Bacteria are transparent, but with Gram stain:
  • Violet color (Gram-positive).
  • Red color (Gram-negative).
• Capsule: May be present or not.
• Spore: May be present or not.
• Motility: Has movement.
• Bacteria in adverse conditions form spores with key components inside.
• Spores increase bacterial survival in harsh conditions, making them hard to eliminate.

Bacterial Classification and Structures

• Arrangement: The arrangement of bacterial cells.
• True Bacteria: Cocci or Bacilli, Gram-positive or Gram-negative.
• Filamentous Bacteria: Streptomyces.
• Mycoplasma: Natural exceptions to cell wall presence.
• Spirochetes: Similar to bacteria.
• Rickettsiae and Chlamydiae: Require a host, and share characters with viruses.

Prokaryotic Cell Structures

• Cell wall.
• Cytoplasmic membrane.
• Ribosomes.
• Nucleoid.
• Some bacteria may have non-essential accessory structures, giving them extra characteristics if present.

Accessory Structures

• Capsule.
• Flagella (organ of motility).
• Fimbria (adhesion-conjugation).
• Inclusion granules.
• Cell Wall: Outermost component, providing rigidity.
• Capsule presence affects cell wall appearance; outermost layer when present.
• Cell wall is multi-layered.
• Cell wall is mainly composed of peptidoglycan.

Cell Wall Differences in Gram-Positive and Gram-Negative Bacteria

• Gram-Positive: Lipoteichoic acid attached to lipid.
• Gram-Negative: Lipopolysaccharide and porin.
• Peptidoglycan Layer: Thick in Gram-positive, thin in Gram-negative.
• Outer Membrane: Absent in Gram-positive, present in Gram-negative.
• Teichoic Acid: Present in Gram-positive, absent in Gram-negative.
• Periplasmic Space: Absent in Gram-positive, present in Gram-negative.

Function of the Cell Wall

• Maintains the bacteria's shape.
• Protects against high osmotic pressure and the outer environment.
• Acts as an antigen, stimulating protective antibody production.
• Teichoic acid in Gram-positive bacteria is a major surface antigen.
• Polysaccharides (O antigen) in lipopolysaccharides in Gram-negative bacteria are major surface antigens.
• Peptidoglycan targets antibacterial drugs such as penicillins and cephalosporins.
• Lipid A in Lipopolysaccharide layer in Gram-negative bacteria is an endotoxin.
• Cell wall contributes to staining properties and cell division.
• Lipid A causes toxicity if the bacteria rupture.

Abnormalities of Cell Wall

• Protoplasts: Complete cell wall removal, cannot revert and are more common in Gram +ve bacteria.
• Created with lysozymes, antibiotics disrupt peptidoglycan synthesis.
• Must be studied in specific conditions to protect them.
• Spheroplasts: Partial removal of cell wall, can revert, more common in Gram -ve.
• L-forms: Bacterial cell variant with deficient cell wall, can occur naturally or induced.
• Can revert to normal when the cell wall inhibitor is removed.
• Causes chronic infections.
• Antibiotics can disrupt the cell wall, leading to increased deficiency; the cell wall is restored if stopped before course completion.
• Mycoplasma: Natural bacteria lacking a cell wall.

Cell Membrane Functions

• Selective permeability to different molecules exchanging nutrients and wastes.
• Active transport of ions and nutrients to achieve osmotic balance.
• Supplies the cell with energy through electron transport and oxidative phosphorylation, i.e. site of respiration.
• Mitochondria not present: produces energy in the form of ATP.

Functions of Cell Membranes Cont'd

• Excretion of hydrolytic exoenzymes.
• Excretion of pathogenicity proteins.
• Provides enzymes and carrier molecules that function in DNA, cell wall, and lipid membrane synthesis.
• Bears receptors and other proteins of the chemotactic and other sensory transduction systems.
• Excretes hydrolytic exoenzymes.
• Pathogenicity proteins excreted include IgA protease.
• Provides enzymes and carrier molecules that function in DNA, cell wall, and lipid membrane synthesis.
• Functions in DNA, cell wall, and lipid membrane synthesis.
• It bears receptors and other proteins of the chemotactic and other sensory transduction systems.

Mesosomes

• Invaginations in the cytoplasmic membrane, Increasing the surface area without increasing size.

Cytoplasm Component Functions

• Increasing surface area.
• Cellular respiration.
• Enzyme excretion.
• Cytoplasm:
  • Ribosomes (70S).
    • 50S large subunit.
    • 30S small subunit.
  • Some antibiotics target ribosomes to stop protein synthesis.
  • Plasmids (extrachromosomal double-stranded circular DNA or accessory DNA).
  • Supplemental genetic material is non-essential.
• Nuclear body: Mass of coiled DNA without a nuclear membrane.
• Single Chromosome (double-stranded).
• No nucleolus; duplicates before cell division.

Structures Outside the Cell Wall

• Capsule: A gelatinous outermost layer (occurs in some bacteria.)
• Composed of polysaccharides mainly and can be polypeptides.
• The capsule hides bacterial antigens, preventing recognition by the immune system, sometimes impeding treatment.
• Glycocalyx (slime layer): A thin coat composed of polysaccharides.
• Adhesion (attachment) and colonization (establishment).
• Flagella: Organ of motility, composed of flagellin protein (antigenic).
• Basal body.
• Types vary with species (one, numerous in one or two places, or all around the cell).
• Fimbriae: Organ of adhesion.
• Composed of piltin protein (antigenic).
• Hair-like projections aid adhesion for: Ordinary pilli and Sex pilli.
• Sex pilli aid in transferring of genetic material (conjugation).

Spores

• Spores develop within bacteria for use in unfavorable conditions.
• Bacteria covers itself to resist changes spores are formed because of calcium presence.
• Sporulation occurs.
• After germination, spores return to their normal state in favorable conditions.
• The are called sporulating bacteria: Bacillus, Clostridium.

Spore Structure

• Nuclear material.
• Small amount of cytoplasm with little water.
• Inner membrane (cytoplasmic membrane).
• Spore cortex (peptidoglycan layer).
• Spore coat (keratin-like protein, the toughest layer).

Resistance of bacterial spores

• Spores are more resistant due to low water/enzyme content and a rigid impermeable wall rich in calcium dipicolinate.
• Spores lack metabolic activity.
• Spores are resistant because of calcium dipicolonate content.

Medical Importance of Spores

• Exhibit extraordinary resistance to heat and chemicals.
• Boiling doesn't destroy spores; autoclaving (121°C for 20-30 minutes) is needed to sterilize instruments.
• Help identify bacteria.
• Spore shape and location of bacteria will help with identification..

Medical Importance of Spores: More info

• Capsules protect pathogenic bacteria against phagocytosis; the slimy capsule makes its difficult for phagocytes to hold firmly on the bacterial surface.
• Using antigenicity of capsules may help with identification.

Bacterial capsules

• Variation in sugar components helps identify and type bacteria.
• Capsule or antigenic part of capsular polysaccharide generates memory antibodies for resistance.
• Vaccines use capsular polysaccharides as immunogens for protective memory antibodies.
• Capsules in certain vaccines help induce protective antibodies
• Capsules aid adherence to other components of the body
• Macrophages that engulf capsulated bacteria trigger antibody formation; macrophages can then target ingested bacteria.