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Questions and Answers
What type of bacteria is described as living on or in the body without causing harm but may become pathogenic under certain conditions?
What type of bacteria is described as living on or in the body without causing harm but may become pathogenic under certain conditions?
Which of the following arrangements describe bacterial cells that remain attached after division?
Which of the following arrangements describe bacterial cells that remain attached after division?
What layer comprises about 50% of the cell wall material in Gram-positive bacteria?
What layer comprises about 50% of the cell wall material in Gram-positive bacteria?
Which structure serves as a rigid support for bacterial cells and protects against osmotic pressure?
Which structure serves as a rigid support for bacterial cells and protects against osmotic pressure?
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Which type of bacterial shape is characterized as spherical?
Which type of bacterial shape is characterized as spherical?
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Which of the following best defines the scope of Medical Microbiology?
Which of the following best defines the scope of Medical Microbiology?
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What is the main difference between prokaryotic and eukaryotic organisms as described in microbiology?
What is the main difference between prokaryotic and eukaryotic organisms as described in microbiology?
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In microbiological nomenclature, how should the genus and species names of microorganisms be formatted?
In microbiological nomenclature, how should the genus and species names of microorganisms be formatted?
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What is the role of saprophytic bacteria as described in the content?
What is the role of saprophytic bacteria as described in the content?
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Which of the following correctly describes the classification of microorganisms that cause infectious diseases?
Which of the following correctly describes the classification of microorganisms that cause infectious diseases?
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Study Notes
Medical Microbiology
- The study of microorganisms that cause infectious diseases in humans, including the human response to those infections.
- Focuses on etiology, pathogenesis, laboratory diagnosis, specific treatment, and control of infection (immunization).
- Includes bacteriology, virology, mycology, immunology and parasitology.
Microorganisms
- Defined as organisms too small to be seen with the naked eye.
- Exist as single cells (unicellular) or in multiple cells (multicellular).
- Include eukaryotes, prokaryotes, viruses and prions.
- Prokaryotic organisms
- Include bacteria.
- Eukaryotic organisms
- Include fungi, protozoa, and helminths as well as humans.
Microbiological Nomenclature
- Uses the binomial system of nomenclature.
- Each species has a generic (genus) and a specific (species) name.
- The genus name is written with a capital letter and the species name with a lowercase letter.
- Names should be italicized in text.
- Example: Bacillus anthracis (B.anthracis)
- Viruses are not named using this system.
Bacteriology
- Bacteria are widely distributed in nature.
- Bacteria are described as:
- Saprophytic bacteria: Live on inanimate material (soil, water, dust, air, clothes, dead bodies, decomposing organic matter).
- Parasitic bacteria: Live on or in the body of living creatures.
- Pathogenic bacteria: Cause disease in humans, animals, or plants.
- Commensal bacteria: Live on or in the body without exerting a harmful effect.
Bacterial Morphology
- Microscopic examination is the first step taken in bacterial identification.
- Features of importance are size, shape, arrangement, and structure.
Size of the Bacterial Cell
- Most bacteria fall within the general dimensions of 0.75 to 4um.
Shape of the Bacterial Cell
- Bacteria are unicellular structures that may occur as:
- Cylindrical (rod-shaped or bacilli)
- Example: E.coli
- Spherical (cocci or coccoid) forms
- Example: Staphylococci
- Coma-shaped (vibrios)
- Example: Vibrio cholera
- Many twists (spiral)
- Example: spirochaetes
- Cylindrical (rod-shaped or bacilli)
Arrangement of Bacteria
- When a bacterial cell divides, the two daughter cells may separate or remain attached to one another.
- Cocci (spherical) can be seen in:
- Clusters: Staphylococci
- Pairs (diplococci): Pneumococci
- Chains: Streptococci
- Bacilli (rod-shaped) can be seen:
- Parallel to each other: Corynebacterium diphtheria
- At an angle to each other: Corynebacterium diphtheria
Bacterial Structure
- There are four main essential components in bacterial cells:
- Cell wall
- Cell (cytoplasmic) membrane
- Cytoplasm
- Nucleoid
Bacterial Cell Wall
- Provides rigid shape and support.
- Protects against osmotic pressure.
- Is the target of some medications (penicillins and cephalosporins)
Gram-Positive Bacteria Cell Wall
- Has a thick peptidoglycan layer, forming about 50% of the cell wall material.
- Peptidoglycan has three layers:
- A backbone of alternating N-acetyl-glucosamine and N-acetylmuramic acid.
- A set of identical tetrapeptide side chains attached to the N-acetylmuramic acid.
- A set of identical peptide cross bridges.
- Contains teichoic acid layer, which is a polymer of glycerol or ribitol phosphate.
- Two types of teichoic acids: wall teichoic acid and membrane teichoic acid.
Functions of Peptidoglycan
- Confers Gram reaction.
- Synthesis is inhibited by penicillins and cephalosporins.
- Degraded by lysozyme.
Functions of Teichoic Acid
- Major surface antigen in Gram-positive bacteria only.
- Induces TNF-α and IL-1 production.
- Facilitates attachment of gram-positive bacteria to mucosal cells.
Gram-Negative Bacteria Cell Wall
- Composed of two layers:
- Inner layer of peptidoglycan, forming only 5-10% of the cell wall material.
- Outer layer of lipopolysaccharides (LPS) or outer membrane.
- Lipoprotein molecules cross-link the peptidoglycan layer and the LPS layer.
- Periplasmic space: A concentrated gel-like matrix between the inner cytoplasmic membrane and the bacterial outer membrane.
- Site of ß-lactamases that degrade penicillins and other ß-lactam drugs.
Lipopolysaccharide (LPS)
- Composed of three units:
- Phospholipid called lipid A: Responsible for toxic effects.
- Core polysaccharide.
- Outer polysaccharide (O antigen): Used to identify certain organisms in the clinical lab.
Functions of LPS
- Endotoxin: Released only when bacterial cells are lysed.
- Activates macrophages.
- Activates B cells without the help of T-cells.
- Used to classify bacteria.
Outer Membrane Proteins (OMPs)
- Have multiple functions:
- Attachment
- Virulence
- Porins: Form transport channels across the outer membrane.
Functions of the Cell Wall
- Maintains the bacteria's shape.
- Protects the cytoplasmic membrane from bursting in hypotonic solutions.
- Detects the response to Gram stain.
- Plays a role in cell division.
Cytoplasmic Membrane
- A semipermeable, double-layered structure surrounding the cytoplasm.
- Lies on the inside of the peptidoglycan layer of the cell wall.
- Composed of phospholipid bilayer with embedded proteins known as penicillin-binding proteins.
Functions of the Cytoplasmic Membrane
- Active transport of molecules into the cell.
- Energy generation by oxidative phosphorylation.
- Synthesis of precursors of the cell wall.
- Secretion of enzymes and toxins.
- Plays a role in DNA replication.
Mesosomes
- Invaginations of the cytoplasmic membrane.
- Play a role in respiration and cell division.
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Description
Explore the fascinating world of medical microbiology, including the study of microorganisms that cause infectious diseases in humans. This quiz covers essential topics such as etiology, pathogenesis, and microbiological nomenclature. Test your knowledge on various microorganisms and their classification!
