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Questions and Answers
Which of the following characteristics distinguishes plasmids from the nucleoid genome in bacteria?
Which of the following characteristics distinguishes plasmids from the nucleoid genome in bacteria?
- Plasmids are composed of flagellin protein.
- Plasmids often carry genes that contribute to virulence or antibiotic resistance. (correct)
- Plasmids always carry genes essential for bacterial survival.
- Plasmids are typically larger in size.
A bacterial capsule is considered a virulence factor because it impairs the ability of bacteria to cause disease.
A bacterial capsule is considered a virulence factor because it impairs the ability of bacteria to cause disease.
False (B)
How does the presence of water within a bacterial capsule contribute to the bacterium's survival?
How does the presence of water within a bacterial capsule contribute to the bacterium's survival?
It protects against desiccation.
Bacteria that possess flagella distributed all over their cell surface are described as having a ___________ arrangement.
Bacteria that possess flagella distributed all over their cell surface are described as having a ___________ arrangement.
Match the type of bacterial flagellar arrangement with its correct description:
Match the type of bacterial flagellar arrangement with its correct description:
What is the primary differentiating factor between Gram-positive and Gram-negative bacteria?
What is the primary differentiating factor between Gram-positive and Gram-negative bacteria?
Teichoic acids are a characteristic component of Gram-negative bacterial cell walls.
Teichoic acids are a characteristic component of Gram-negative bacterial cell walls.
What is the primary function of the bacterial cell wall in relation to osmotic pressure?
What is the primary function of the bacterial cell wall in relation to osmotic pressure?
The outer membrane of Gram-negative bacteria contains a significant amount of ______, which contributes to its structural integrity.
The outer membrane of Gram-negative bacteria contains a significant amount of ______, which contributes to its structural integrity.
Which of the following is NOT a function of the bacterial cell wall?
Which of the following is NOT a function of the bacterial cell wall?
Match the component to the cell type:
Match the component to the cell type:
What cellular structure is the site of protein synthesis in bacterial cells and is sensitive to antibiotics like streptomycin?
What cellular structure is the site of protein synthesis in bacterial cells and is sensitive to antibiotics like streptomycin?
Plasmids are essential for bacterial survival under all environmental conditions.
Plasmids are essential for bacterial survival under all environmental conditions.
Which of the following bacterial arrangements describes cocci in a cluster formation?
Which of the following bacterial arrangements describes cocci in a cluster formation?
All cells, including bacteria, protozoa and fungi, have a well-defined nucleus.
All cells, including bacteria, protozoa and fungi, have a well-defined nucleus.
What is the primary function of the bacterial cell membrane?
What is the primary function of the bacterial cell membrane?
The cell wall of bacteria primarily consists of a substance called ________.
The cell wall of bacteria primarily consists of a substance called ________.
Match the following bacterial shapes with their descriptions:
Match the following bacterial shapes with their descriptions:
If a microbiologist is examining a bacterium under a microscope and observes flagella, what can they infer about the bacterium?
If a microbiologist is examining a bacterium under a microscope and observes flagella, what can they infer about the bacterium?
Which of the following best describes the bacterial cell envelope?
Which of the following best describes the bacterial cell envelope?
What two monosaccharides make up peptidoglycan?
What two monosaccharides make up peptidoglycan?
What is the primary function of an endospore in bacteria?
What is the primary function of an endospore in bacteria?
Viral capsids are composed of diverse types of proteins arranged asymmetrically to maximize variability in host cell recognition.
Viral capsids are composed of diverse types of proteins arranged asymmetrically to maximize variability in host cell recognition.
Describe two key functions of viral capsids.
Describe two key functions of viral capsids.
A _ is a hardened mass of mycelium that generally serves as an overwintering stage for fungi.
A _ is a hardened mass of mycelium that generally serves as an overwintering stage for fungi.
Match the fungal structure with its description:
Match the fungal structure with its description:
What is the correct sequence of steps when using a light microscope?
What is the correct sequence of steps when using a light microscope?
After adding oil to a slide when using a microscope, it is acceptable to return to lower magnification powers without cleaning the objective lens.
After adding oil to a slide when using a microscope, it is acceptable to return to lower magnification powers without cleaning the objective lens.
In a light microscope, which lens initially magnifies the image of the specimen?
In a light microscope, which lens initially magnifies the image of the specimen?
What is the primary reason Gram-positive bacteria retain the crystal violet-iodine complex during Gram staining?
What is the primary reason Gram-positive bacteria retain the crystal violet-iodine complex during Gram staining?
Gram-negative bacteria appear blue to purple after Gram staining due to their thick peptidoglycan layer retaining the crystal violet stain.
Gram-negative bacteria appear blue to purple after Gram staining due to their thick peptidoglycan layer retaining the crystal violet stain.
What decolorizing agent is typically used in the Gram staining procedure to differentiate between Gram-positive and Gram-negative bacteria?
What decolorizing agent is typically used in the Gram staining procedure to differentiate between Gram-positive and Gram-negative bacteria?
In acid-fast staining, acid-fast bacteria resist ______ by acid once stained.
In acid-fast staining, acid-fast bacteria resist ______ by acid once stained.
Match the following bacteria with their Gram stain reaction and morphology:
Match the following bacteria with their Gram stain reaction and morphology:
What happens if you use the coarse adjustment knob on a microscope with high magnification?
What happens if you use the coarse adjustment knob on a microscope with high magnification?
If a microscope has an ocular lens of 10x and an objective lens of 60x, what is the total magnification?
If a microscope has an ocular lens of 10x and an objective lens of 60x, what is the total magnification?
Microbial staining is unnecessary when using a light microscope because microbial cytoplasm is easily visible.
Microbial staining is unnecessary when using a light microscope because microbial cytoplasm is easily visible.
Which of the following is NOT a purpose of microbial staining?
Which of the following is NOT a purpose of microbial staining?
In ___________ staining, only one dye is used to stain a microorganism.
In ___________ staining, only one dye is used to stain a microorganism.
Which type of dye carries a positive electrical charge and is used in direct staining methods?
Which type of dye carries a positive electrical charge and is used in direct staining methods?
Why do acidic dyes not stain bacterial cells in an indirect staining method?
Why do acidic dyes not stain bacterial cells in an indirect staining method?
What is the purpose of a counterstain in differential staining?
What is the purpose of a counterstain in differential staining?
Flashcards
Eukaryotic Cells
Eukaryotic Cells
Cells with a well-defined nucleus.
Prokaryotic Cells
Prokaryotic Cells
Cells lacking a nucleus.
Coccus Bacteria
Coccus Bacteria
Spherical-shaped bacteria.
Bacillus Bacteria
Bacillus Bacteria
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Streptococcus
Streptococcus
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Staphylococcus
Staphylococcus
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Cell Envelope
Cell Envelope
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Cytoplasmic Membrane
Cytoplasmic Membrane
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Bacterial Cell Walls
Bacterial Cell Walls
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Cell Wall Functions
Cell Wall Functions
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Gram-Positive Cell Wall
Gram-Positive Cell Wall
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Teichoic Acids
Teichoic Acids
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Gram-Negative Cell Wall
Gram-Negative Cell Wall
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Lipopolysaccharide (LPS)
Lipopolysaccharide (LPS)
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Cytoplasm
Cytoplasm
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Plasmids
Plasmids
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Capsule (Glycocalyx)
Capsule (Glycocalyx)
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Flagella
Flagella
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Monotrichous
Monotrichous
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Pili
Pili
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Gram Stain
Gram Stain
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Gram-Positive Bacteria
Gram-Positive Bacteria
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Gram-Negative Bacteria
Gram-Negative Bacteria
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Acid-Fast Stain
Acid-Fast Stain
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Non-Acid-Fast Bacteria
Non-Acid-Fast Bacteria
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High Magnification Knob
High Magnification Knob
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Total Magnification
Total Magnification
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Ocular Lens Magnification
Ocular Lens Magnification
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Microbial Staining
Microbial Staining
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Simple Staining
Simple Staining
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Direct Staining
Direct Staining
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Indirect Staining
Indirect Staining
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Differential Stains
Differential Stains
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Endospore
Endospore
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Capsid
Capsid
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Capsid Function
Capsid Function
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Fungal Body Forms
Fungal Body Forms
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Sclerotium
Sclerotium
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Mycelium
Mycelium
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Microscope Lenses
Microscope Lenses
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Microscopy Procedure
Microscopy Procedure
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Study Notes
- Lecture is about Microbial Structure and Microscopy.
- The lecture aims to provide knowledge on bacterial shapes, arrangements, structures, and their functions.
- The lecture will cover the differences between Gram-positive and Gram-negative bacteria.
- The lecture will focus on differences between bacterial, viral, and fungal structures.
- In the lecture, how to use a light microscope will be explained.
- Microbial staining types will be mentioned.
Introduction
- The cellular world is divided into two major groups based on the presence of a nucleus.
- Eukaryotic cells have a well-defined nucleus.
- Prokaryotic cells lack a nucleus.
- Bacteria are prokaryotes.
- Fungi and protozoa are eukaryotes.
Bacterial Structure & Arrangements
- Coccus: Spherical shape; can form chains (Streptococcus) or clusters (Staphylococcus).
- Bacillus: Rod shape; can form chains (Streptobacillus).
- Coccobacillus: An oval shape, between coccus and bacillus.
- Vibrio: Curved shape.
- Spirillum: Spiral shape.
- Spirochete: Flexible, spiral shape.
Essential Structures
- Cell Wall: Provides structure and protection.
- Cell Membrane: Regulates passage of substances in and out of the cell.
- Cytoplasm: Gel-like substance inside the cell containing various structures.
- Nuclear Material: Includes DNA, which carries genetic information.
Particular Structures
- Capsule: Provides protection and aids in attachment.
- Flagella: Facilitates movement.
- Pili: Involved in attachment and genetic exchange.
- Spores: Dormant structures that allow survival in harsh conditions.
Cell Envelope
- It consists of all the material external to, and enclosing the cytoplasm of a bacterial cell.
- It consists of the cell wall, and the cytoplasmic membrane.
- Capsules and pili are also included in the cell envelope when present.
Cytoplasmic Membrane
- Also known as the cell membrane.
- It is composed of phospholipids arranged in a lipid bilayer.
- It is flexible and easily ruptured.
- It acts as a permeability barrier, controlling the entry and exit of molecules.
Cell Wall
- It's primary structure is peptidoglycan, a repeating sugar molecule.
- Key components include: N-acetyl glucosamine (NAG) and N-acetyl muramic acid (NAM).
- Meshwork held together by small peptide chains, forming inter-bridge structures.
- Two main types exist: Gram-positive and Gram-negative, differentiated by Gram staining characteristics.
Functions of the Cell Wall
- It provides flexibility and maintains cell shape and rigidity.
- It counters the effects of osmotic pressure.
- It facilitates the movement of gases and water in and out of cells.
- Rigid platform for surface appendages (flagella and pili).
- Cell division (binary fission) is also helped by the cell wall.
- Major antigenic determinants on the cell surface are also contained.
- It has antibiotic resistance.
Gram-Positive Bacteria Cell Wall
- Has a thick peptidoglycan layer.
- 90% of the cell wall consists of peptidoglycan, retaining crystal violet dye during Gram staining.
- Composed of polysaccharides, including teichoic acid and lipoteichoic acid.
Gram-Negative Bacteria Cell Wall
- Has a thin peptidoglycan layer surrounded by an outer membrane.
- The outer membrane is composed of lipids, lipoproteins, and lipopolysaccharide (LPS).
- Contains no teichoic acids.
- The outer membrane is composed of lipopolysaccharides.
- The Periplasmic space differs from gram-positive cells, containing many enzymes.
Gram-Positive vs. Gram-Negative Bacteria
- Peptidoglycan Layer: Thick in Gram-positive, thin in Gram-negative.
- Teichoic Acid: Present in Gram-positive, absent in Gram-negative.
- Lipids: Very little in Gram-positive, lipopolysaccharide layer in Gram-negative.
- Outer Membrane: Absent in Gram-positive, present in Gram-negative.
- Toxins: Exotoxins in Gram-positive, endotoxins in Gram-negative.
- Antibiotic Sensitivity: Very sensitive in Gram-positive, moderately sensitive in Gram-negative.
Cytoplasm
- It is composed largely of water, proteins, nucleic acids, lipid enzymes, coenzymes, and organic as well as inorganic solutes, with small amounts of sugars and salts.
- Ribosomes occur in copious amounts, range from 15-20nm in diameter with 70S; distributed throughout the cytoplasm.
- Streptomycin and erythromycin are sensitive ribosomes, the site of protein synthesis.
Nuclear Material
- It is concentrated in a region called the nucleoid within the cytoplasm.
- This region has no membrane-bound nucleus.
- Double strand DNA is located within a specialized region of the cytoplasm.
- Plasmids are small, circular, self-replicating loops of DNA.
- Plasmids carry the infection-causing gene (Virulence factor).
- Plasmids provide antibiotic resistance.
Capsule (Glycocalyx)
- Sharply defined structures that exist around the cell surface.
- Well-organized layers that doesn't wash off easily.
- Usually made up of polysaccharides.
- It is a virulence factor that enhances the ability of bacteria to cause disease.
- Protects bacteria from desiccation.
Appendages
- Hair-like parts projecting from the cell wall.
- Flagella are long, semi-rigid, and helical.
- Hollow tubular made of protein flagellin.
- Bacteria move in a directed way through their function,.
- They are antigenic.
- Cells may have one or many flagella.
- Monotrichous flagella has one flagella.
- Lophotrichous flagella have a tuft at one end.
- Amphitrichous flagella have on both ends.
- Peritrichous flagella are all around.
- Pili are shorter and thinner than flagella.
- Attachment structures that promote specific cell to cell contact via their function.
- The bacterial cell and the host eukaryotic cell, or between one bacterial cell and another via attachment.
Endospores
- Thick-coated, resistant structure,
- Contains bacterial DNA.
- Harsh conditions can destroy most of the cell, however the endospore may survive,
- When favorable conditions return, they give rise to new bacterial cells.
Viral Structure
- Size varies from 17 nm to 3000 nm in diameter.
- The basic shape is either rod-like or spherical.
- The protective shell, or capsid, is made of many identical protein subunits and can be symmetrically organized.
- The viral genome can be either DNA or RNA, single-stranded or double-stranded.
- Virus capsids aid in packaging and protecting nucleic acid
- Virus capsids has role in Host cell recognition
- Virus capsids delives Genomic material
Fungal Structure
- Body form can be Unicellular, filamentous (tube-like strands called hyphae).
- Mycelium = aggregate of hyphae.
- Sclerotium = hardened mass of mycelium, serves as a stage through winter.
- Multicellular, mycelial cords, rhizomorphs, and fruit bodies/mushrooms.
Microscopy
- The body tube of ocular and objective lens focuses the image.
- The objective (bottom) convex lens magnifies and focuses (bends) the image inside the body tube.
- The ocular convex (top) lens of a microscope magnifies it again.
- To use a microscope, put the the slide on a stage and secure by the lock clips.
- Start with the the lowest magnification power (x4, x10, x40, x100 (with oil).
- Adjust light source.
- Don't move to the next magnification power if you can't focus on the previous one.
- Don't return to the lower magnification power if oil is added.
- Don't use the coarse adjustment knob on high magnification.
- To focus a sample, use the fine adjustment.
- The ocular lens us multiplied with the the objective lens,
- for example if the ocular is 10x and the objective is 40x the magnification power is 400x.
Microscopy
Microbial Staining
- It is transparent which it is necessary to stain microorganisms before viewing them using light microscope
- To study different parts of microbes (Bacteria & Fungi), use different staining techniques.
- Differential staining (e.g., Gram stain) is the most common, for Classification of Microorganisms.
- Classification of Microorganisms facilitates successful diagnosis so the cause of infection is determined.
- Stains are categorized into Simple Staining or Differential Staining
- Simple Staining Technique employs only one dye (stain).
- Direct Staining Method uses basic dyes (stains) that carry +ve electrical charges (e.g: crystal violet, safranin, Methylene Blue, malachite green,...etc.
- Indirect Staining method uses acidic dyes (carrying -ve charges) which do not stain the bacterial cells due to repulsion (e.g,. nigrosin).
- Differential Stainings includes using 2 types of dyes (stains).
- In Differential Stainings the first stain is principal stain and the second one is counter stain to stain unstained cells (e.g. Gram and acid fast staining technique).
- used Differential stains differentiats two different bacteria ( gram-positive or gram-negative) in a sample.
Gram Stain
- Hans Christian Gram, a Danish physician, developed the Gram stain procedure in 1882, this is done to differentiate between gram positive and gram negative organisms
- The differentiation is based on cell wall makeup.
- Exploits the basic differences in the outer layers of bacteria so that other bacterial groups can keep initial stain, losing the dye during the process of decolorization.
- Bacterial cells that lose color during the step of decolorization will keep the color of the counterstain.
- gram-positive cells will appear blue/purple while gram-negative cells will apear pink/red.
- Gram-positive has a very thick peptidoglycan cell wall (a layer of sugars and amino acids) that is able to withhold crystal violet-iodine during staining, while Gram-negative cells have a thin a thin peptidoglycan cell wall.
- Gram positive cells do not decolorize with a short burst of ethanol.
- After ethanol, gram negative cells accept counter stain safranin.
Other Differential Staining Methods
- Acid-fast stain, clinical application to detect members of the Mycobacterium.
- M. tuberculosis, the etiologic agent of tuberculosis, is the most common pathogen of this group.
- The Nocardia can be identified by it's acid-fast characteristic.
- The term acid-fast is derived from the resistance displayed by acid-fast bacteria to decolorization by acid once they have been stained by another dye.
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Description
Explore bacterial cell structures: plasmids vs. nucleoid genome, capsule virulence, flagellar arrangements. Differentiate Gram-positive and Gram-negative bacteria based on cell wall composition and teichoic acids. Understand the role of the cell wall in osmotic pressure regulation.