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Questions and Answers
Which of these options were developed to improve contrast differences between cells and the surrounding medium, making it possible to see living cells without staining?
Which of these options were developed to improve contrast differences between cells and the surrounding medium, making it possible to see living cells without staining?
What is the name of the structure that is found in all bacteria, that surrounds the cytoplasm and maintains the shape of the cell?
What is the name of the structure that is found in all bacteria, that surrounds the cytoplasm and maintains the shape of the cell?
Cell wall
Prokaryotic cells have a membrane-covered nucleus which stores the cell's DNA.
Prokaryotic cells have a membrane-covered nucleus which stores the cell's DNA.
False
Which of the following are types of prokaryotic flagellar arrangements?(Select all that apply)
Which of the following are types of prokaryotic flagellar arrangements?(Select all that apply)
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Which of the following types of microscopes uses a beam of electrons projected from an electron gun?
Which of the following types of microscopes uses a beam of electrons projected from an electron gun?
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What is the name of the process by which a bacteria forms an endospore?
What is the name of the process by which a bacteria forms an endospore?
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Which of the following structures is NOT a component of a prokaryotic cell?
Which of the following structures is NOT a component of a prokaryotic cell?
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The [BLANK] component of the outer membrane consists of sugars (O polysaccharides) that function as antigens and lipid A, which is an endotoxin.
The [BLANK] component of the outer membrane consists of sugars (O polysaccharides) that function as antigens and lipid A, which is an endotoxin.
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What category of antibiotics target cell wall synthesis?
What category of antibiotics target cell wall synthesis?
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Which of the following stains is useful for differentiating between Gram-positive and Gram-negative bacteria?
Which of the following stains is useful for differentiating between Gram-positive and Gram-negative bacteria?
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Match the following types of bacteria with their corresponding cell wall structure:
Match the following types of bacteria with their corresponding cell wall structure:
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What type of movement is exhibited when a bacteria moves towards an attractant?
What type of movement is exhibited when a bacteria moves towards an attractant?
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The outer membrane of Gram-negative bacteria protects the cell from phagocytosis.
The outer membrane of Gram-negative bacteria protects the cell from phagocytosis.
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Which of the following is a function of ribosomes?
Which of the following is a function of ribosomes?
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What is the name of the structure that helps bacteria to adhere to surfaces?
What is the name of the structure that helps bacteria to adhere to surfaces?
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Mesosomes are infoldings of the plasma membrane that are artifacts and not true cell structures.
Mesosomes are infoldings of the plasma membrane that are artifacts and not true cell structures.
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Which of the following is a function of the outer membrane in Gram-negative bacteria?
Which of the following is a function of the outer membrane in Gram-negative bacteria?
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What is the unit of measurement for bacterial morphology?
What is the unit of measurement for bacterial morphology?
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The cytoplasm of a prokaryote contains numerous [BLANK] ribosomes.
The cytoplasm of a prokaryote contains numerous [BLANK] ribosomes.
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Prokaryotic flagella rotate to pull the cell.
Prokaryotic flagella rotate to pull the cell.
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The resolving power of the light microscope under ideal conditions is about half the wavelength of the light being used.
The resolving power of the light microscope under ideal conditions is about half the wavelength of the light being used.
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What is the name of the process by which a bacteria returns to its vegetative state from an endospore?
What is the name of the process by which a bacteria returns to its vegetative state from an endospore?
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Study Notes
Lecture 1: Bacterial Morphology and Structures, Metabolism & Growth
- Cell structure: Covers eukaryotic and prokaryotic cells' basic structures and functions.
- Techniques to study morphology of bacteria: Includes optical methods (light, phase contrast, dark-field, fluorescent, electron, confocal scanning laser microscopy)
- Bacterial cell wall structures and properties: Discusses Gram-positive/negative cell walls, acid-fast cell walls, and archaea cell walls.
- Protoplasts, spheroplasts, and L-forms: Explains these variations of bacterial cells.
- Peptidoglycan, LPS, pathogenesis, and antibiotic targets: Details these components and their roles in bacterial infections and treatments.
- Bacterial cell structure and genetics: Includes chromosome, plasmid, ribosomes, and their roles in pathogenesis and drug resistance.
- Bacterial morphology in clinical diagnosis Explains the versatility of bacteria in diagnosing diseases.
- Bacterial appendages, spores, capsules, flagella, pili etc., and their applications in clinical practice: Details their functions.
History of Microbiology
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Robert Hooke (1665):
- First report of cell structure.
- Published "Micrographia," the first illustrated book on microscopy, including his observations.
- Observed "little boxes" in cork, coining the term "cell."
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Anton Van Leeuwenhoek (1678):
- First person to see bacteria.
- Used a single-lens microscope.
Spontaneous Generation
- Aristotle (384 a.C.): Proposed that living things could arise from non-living material (miasma - "bad air").
- Miasma was a belief amongst people that diseases came from foul air and bad odors.
- Phoenix myths: Refers to mythical long-lived birds that regenerate.
- Golam: A clay figure believed to come to life through magic.
- Herodotus (c. 484 – c. 425 BC): Claimed living organisms could arise from non-living materials, like crocodiles from mud.
- Van Helmont (17th century): Suggested small animals arise from non-living materials, like maggots from meat and mice from feed.
Lazzaro Spallanzani (1729-1799)
- Experiments: Demonstrated that boiling broth in sealed flasks prevented microbial growth.
Swan Neck Flask Experiment (Pasteur)
- Experiment procedure: Showed that no growth occurred in swan neck flasks until they were broken.
- Conclusion: microbes in the dust not in the air.
Louis Pasteur (1822-1895)
- Germ theory: Proposed that microorganisms cause disease.
- Fermentation: Discovered roles of microorganisms in fermentation processes.
- Pasteurization: Developed a process to kill microorganisms in liquids.
- Rabies vaccine: Created the first rabies vaccine.
- Streptococcus pneumonia causes lobar pneumonia: Further established the connection between microbes and diseases.
Vaccination
- Pasteur's rabies vaccine (1885): Developed and used on a boy.
- Treatment method: Attenuated virus in rabbits, then harvested from their spinal cords and used on the boy.
Robert Koch (1843-1910)
- Confirmed germ theory: Helped establish germ theory of disease.
- Discovered cause of anthrax, cholera, and tuberculosis Identifies the pathogens causing diseases.
- Developed culture techniques: Methods for growing pure cultures, staining, and solid media.
Koch's Postulates
- Rules to prove disease cause: Establish relationship between microbe and disease.
- Organism consistently isolated from diseased individuals: Must be found in abundance in diseased and absent on healthy.
- Organism cultivated in pure form: Must be isolated and grown in pure culture.
- Signs and symptoms induced after inoculation: Must cause disease when introduced to healthy hosts.
- Same organism isolated from experimentally infected individual: Must be reisolated from the inoculated, diseased experimental host and identified as the original causative agent.
Bacterial Cell Morphology
- Cocci: Spherical bacteria (1µm)
- Bacilli: Rod-shaped bacteria (0.5-1µm wide, 3µm long)
- Spiral bacteria: Spiraled bacteria (1~3µm and 0.3 -0.6µm)
- Unit for measurement Micron or micrometer, μm (1μm = 10–³ mm).
- Size variation: Dependent on bacterial kind and external environment
Bacterial Shapes and Arrangements
- Cocci: Spherical bacteria, can be diplococci (pairs), streptococci (chains), tetrads (groups of four), sarcinae (groups of eight), and staphylococci (clusters).
- Bacilli: Rod-shaped bacteria can be diplobacilli (paired), streptobacilli (chains), and coccobacilli (short, coccus-like rods).
- Spiral Bacteria: Includes vibrios (curved rods) and spirilla (rigid spirals) and spirochetes (flexible spirals).
- Arrangement of Coci, Arrangement of Bacilli, Arrangement of Spiral bacteria.
Other bacterial shapes (Archea)
- Star-shaped bacteria
- Rectangular bacteria
Bacterial Cell Morphology: Essential Structures
- Cell wall: Provides protection and shape
- Cell membrane: Selectively permeable barrier
- Cytoplasm: Fluid component within the cell
- Nuclear Material: Contains bacterial genetic material
Bacterial Cell Morphology: Particular Structures
- Capsule: Outer layer of some bacteria, helping with protection and adhesion.
- Flagella: Whip-like appendages facilitating movement
- Pili: Hair-like structures often involved in DNA transfer and adhesion.
- Spore: Inactive, resistant structure forming during unfavorable conditions.
Bacterial Structure
- Bacterial cytoplasm: Surrounded by the plasma membrane and the cell wall.
- Cell wall: Maintains shape.
- DNA of single DNA resides in nucleoid.
- Ribosomes build proteins in the cell.
- Key components: Cytoplasm, Cell wall, Plasma membrane, Nucleic material, Capsule, Pili, Flagella, Spore.
Techniques to Study Bacterial Morphology – Microscopy
- Light microscopy
- Dark-field microscopy
- Phase-contrast microscopy
- Luminescent microscopy
- Electron microscopy
- Scanning electron microscopy
The Light Microscope
- Resolving power (RP): Distance between two points at which they are visible as separate images. RP is dependent on wavelength of the light source.
- Useful magnification: The magnification required to visualize smallest resolvable objects.
The Bright-field Microscope
- General use: Commonly employed in microbiological studies.
- Magnification: Often uses a 100x objective lens combined with 10x ocular lens for a 1000x magnification, to observe bacteria.
- Contrast: Staining is commonly used to enhance contrast, making bacteria more visible.
The Phase-contrast Microscope
- Improvement over light microscopy: Improves contrast in transparent material (living cells) reducing the need for staining, allowing observing living cells.
- Mechanism: Uses a special ring in the objective lens that amplifies the phase differences to create a dark image on a light background.
The Dark-field Microscope
- Image generated: Highlights the edge of specimen against a dark background creating visual contrast for organisms difficult to visualize without staining.
The Fluorescence Microscope
- Mechanism: Absorbs short wavelengths (UV light), emits longer wavelengths (visible light).
- Application: Used for visualizing fluorescent molecules or staining, often used in clinical diagnostic microbiology.
Differential Interference Contrast Microscopy
- Enhancement of contrast: Provides detailed visualization of transparent cellular structures such as spores, vacuoles, and granules. Produces a three dimensional appearance to internal cell structures.
The Electron Microscope
- High resolution: Electrons have shorter wavelengths than light photons, which provides higher resolution images.
-
Types:
- Transmission electron microscope (TEM): Provides detailed internal structures.
- Scanning electron microscope (SEM): Provides detailed surface structure.
Gram Staining
- Purpose: Differentiates between Gram-positive and Gram-negative bacteria.
- Mechanism: Uses multiple dyes (crystal violet, iodine, decolorizer, safranin) for staining and decolorization, to develop contrast between the two cell types.
Cell Wall
- Composition: Consists of peptidoglycan.
- Protection: Protects bacterial cell from water pressure and mechanical stresses.
- Penicillin function: Interfere with peptidoglycan synthesis.
- Gram-positive vs. Gram-negative cell wall structure differences Gram-positive have thick layer of peptidoglycan, while Gram-negative have thin layer of peptidoglycan and outer membrane lipids.
Gram-positive Cell Wall
- Composition: Multiple layers of peptidoglycan and teichoic acids.
- Teichoic acid functions: Anchoring, cation regulation, and antigenic properties.
Gram-negative Cell Wall
- Composition: A thin peptidoglycan layer and an outer membrane containing lipopolysaccharide, proteins, and phospholipids.
- Lipopolysaccharide (LPS): Antigenic components. Involved in pathogenesis.
- Porins: Channels in the outer membrane that allow small molecules to pass.
Cell Wall Functions in Gram Negative Cells
- Protection: Protects from phagocytosis and harmful chemical agents.
- Permeability: Porins and channel proteins control permeability.
- Toxicity: Lipopolysaccharide (LPS) component is an endotoxin and triggers fever and shock (pathogenicity).
Gram Stain Mechanism
- Steps of gram stain: Primary stain (crystal violet), mordant (iodine), decolorizer (alcohol/acetone), counterstain (safranin).
- Gram-positive reactions: Retain the crystal violet stain, appearing purple.
- Gram-negative reactions: Lose the crystal violet stain and take up the counterstain, appearing pink.
Comparative Characters of Gram-positive and Gram-negative Bacteria
- Descriptions of differences: Summarization of significant differences in structure, biochemical features, and functional differences of Gram-positive and Gram-negative bacteria. Explains factors like Gram reaction type, cell wall layers, and other differences.
Atypical Cell Walls
- Mycoplasma: Lacks cell walls, using sterols in their plasma membranes as protection from osmotic lysis.
- Mycobacterium: Contains mycolic acids in their cell walls, giving it a "waxy" cell wall resistant to acid-alcohol decolorization.
- Archea: Possesses pseudomurein instead of peptidoglycan
Damage of the Cell Wall
- Lysozyme effects: Destroys peptidoglycan in Gram-positive bacterial cell walls.
- Spheroplasts: Remaining structures after damage to Gram-negative outer membrane cells.
- Osmotic lysis: Damage to cell walls leads to osmotic pressure differential and lysis.
- L forms: Spontaneous loss of cell wall in some bacteria, exhibiting unique characteristics allowing survival, growth and division.
Structures External to the Cell Wall – Glycocalyx
- Composition: Specialized polysaccharides and/or polypeptides covering the cell wall.
- Capsule: Organized and firmly attached, providing protection, adhesion, and nutrient source.
- Slime layer: Unorganized and loosely attached, providing nutrient source or protection.
- Extracellular polymeric substances (EPS) are component of glycocalyx and biofilms,
Structures External to the Cell Wall – Flagella
- Structure: Long, thread-like, filamentous appendages with hook and basal body.
- Function: Movement.
- Types: Monotrichous, Lophotrichous, Amphitrichous, Peritrichous.
- Taxis: Positive or negative movement towards/away from stimuli (attractants/repellents).
Bacterial Flagellum structure
- Anchoring mechanism: Different in gram positive and gram-negative bacteria.
- Filament: Composed of flagellin protein and a hollow core.
Axial Filaments
- Structure: Similar to flagella, wrapped around the cell.
- Function: Movement in spirochetes.
Fimbriae and Pili
- Structure: Short, thin appendages.
- Function: Adherence to surfaces (fimbriae) and DNA transfer (pili).
Structure of Inner Cell Wall – Plasma Membrane
- Structure: phospholipid bilayer with peripheral and integral proteins (fluid mosaic model).
- Permeability: Selectively permeable barrier.
- Enzymes: Contains enzymes for many metabolic reactions in prokaryotes (nutrient breakdown, energy production).
Chromatophores
- Structure: Infoldings of the plasma membrane containing pigments.
- Function: Photosynthesis.
- Mesosomes: Infoldings in the plasma membrane, are artifacts, not true cell structures.
Comparison of Prokaryotes and Eukaryotes
- Key differences: Summarizes major structural and functional characteristics comparing the two types of cells. (Size, nucleus, organelles, flagella, cell wall, plasma membrane...).
Cytoplasm and Nucleus
- Cytoplasm: Fluid component inside the plasma membrane, containing water, inorganic and organic compounds, DNA, ribosomes, inclusions (reserve deposits).
- Nucleoid: Bacterial genomic area containing the circular chromosome.
- Plasmids: Optional extra-chromosomal genetic elements; circular DNA molecules, and found only in bacteria.
Ribosomes
- Prokaryotic ribosomes: 70S (small 30S + large 50S subunits)
- Eukaryotic ribosomes: 80S (small 40S + large 60S subunits).
- Targeting with antibiotics: Differing ribosome subunit structure utilized for antibiotic selective targeting
Inclusions
- Examples of bacterial inclusions; various reserve deposits, like phosphate, glycogen, starch, sulfur, carboxysomes, magnetosomes (Fe3O4), and gas vacuoles.
Endospores
- Formation: Sporulation. A process where bacteria form endospores, a resting, inert form of themselves, to endure harsh environmental conditions, lack of nutrients etc.
- Germination: Return of an endospore to its vegetative state
- Genera Bacillus and Clostridium are examples
Targets of Antibiotics
- Cell wall synthesis inhibitors (e.g., penicillins, vancomycin)
- DNA synthesis inhibitors (e.g., metronidazole, quinolones)
- RNA polymerase inhibitors (e.g., rifampicin)
- Ribosomes inhibitors (e.g., aminoglycosides, tetracyclines)
- Cytoplasmic membrane inhibitors (e.g., polymyxins).
Molecular approach in clinical diagnostic
- Molecular identification: Use of DNA sequencing for accurate identification.
- Method: Specimen selection, cultivation, DNA isolation, quality control and DNA processing, sequencing, analysis, summarizing data into a diagnostic report, and utilizing reference databases for analysis.
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