Lecture 1 Flashcards
What forms the cell wall of bacteria?
Peptidoglycan
What repeating units is the peotidoglycan layer made up of?
These repeating units are joined by what cross bridges?
What is the function of the peptidoglycan layer
The peptidoglycan layer is thin in gram positives and thick in gram negatives true or false?
•made up of Repeating units of N- acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
N-acetylglucosamine (NAG)
• N: N-acetyl • A: Think of “Amino sugar” because glucosamine is an amino sugar derived from glucose. • G: Glucosamine, a derivative of glucose.
N-acetylmuramic acid (NAM)
• N: N-acetyl • A: Acid, specifically muramic acid. • M: Muramic acid, which is derived from lactic acid linked to N-acetylglucosamine.
•these repeating units are joined by Peptide cross-bridges
•Provide strength and rigidity and protection to cell
False
•Thick in Gram positive
•Thin among Gram negative
What is the difference between lipopolysaccharide and peptidoglycan layer
Where is the peptidoglycan layer located in gram negative bacteria
What are the three components of lipopolysaccharide ?
Which component of lipopolysaccharide is responsible for the toxic effects of Lipopolysaccharides and is a hydrophobic anchor that is embedded in the outer membrane?
Which component of lipopolysaccharide is a short branched chain of sugars that connects the other two parts of the lipopolysaccharide together?
Which component of lipopolysaccharide is a long polysaccharide chain that extends outward from the cell and helps bacteria evade the host immune system?
Which component of lipopolysaccharide triggers strong immune responses in the host?
Lipopolysaccharides (LPS) and peptidoglycan are both key structural components of bacterial cell walls, but they have different compositions, functions, and are found in different types of bacteria.
-
Location:
- Found in the outer membrane of Gram-negative bacteria.
-
Composition:
- Consists of three main components:
- Lipid A: The hydrophobic anchor that is embedded in the outer membrane. It is responsible for the toxic effects of LPS (endotoxin).
- Core polysaccharide: A short, branched chain of sugars that connects lipid A to the O-antigen.
- O-antigen: A long polysaccharide chain that extends outward from the cell. It varies greatly among different bacterial species and helps in evading the host immune response.
- Consists of three main components:
-
Function:
- Provides structural integrity to the outer membrane.
- Acts as a barrier to protect against harmful substances, including antibiotics and detergents.
- The O-antigen part helps bacteria evade the host immune system.
- Lipid A component triggers strong immune responses in the host, which can lead to fever and septic shock.
-
Location:
- Found in the cell wall of both Gram-positive and Gram-negative bacteria.
- In Gram-positive bacteria, it is thick and forms the major component of the cell wall.
- In Gram-negative bacteria, it is thinner and located between the inner cytoplasmic membrane and the outer membrane.
-
Composition:
- Made of repeating disaccharide units (N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)) linked by β-1,4-glycosidic bonds.
- These sugar chains are cross-linked by short peptides, forming a mesh-like structure.
-
Function:
- Provides rigidity and shape to the bacterial cell.
- Protects against osmotic pressure and mechanical stress.
- In Gram-positive bacteria, it is involved in the regulation of cell growth and division.
During cell division, the peptidoglycan layer helps form a division septum, the new cell wall that separates the daughter cells
- Location: LPS is found only in Gram-negative bacteria, while peptidoglycan is found in both Gram-positive and Gram-negative bacteria.
- Structure: LPS is a complex molecule consisting of lipid A, core polysaccharide, and O-antigen, whereas peptidoglycan is a polymer of sugars and amino acids.
- Function: LPS serves as a protective barrier and a trigger for immune responses, while peptidoglycan provides structural support and protection against physical damage.
Which bacteria doesn’t have cell wall?
Every bacteria has a cell wall except Cell wall defective bacteria(chlamydia and mycoplasma)
What is the cell membrane of bacteria made up of?
Which bacteria is the only one that has sterols in their cell membrane?
State four functions of cell membrane
Made up of Phospholipid and proteins. Bacteria don’t have cholesterol in their cell membranes
•No sterols. Mycoplasmas are the only bacteria that have sterols in their cell membrane (they pick the cholesterol from their environment and put it in the cell membrane) but other bacteria have sterols in their cell wall . This is because they don’t have a cell wall so the sterol is what gives the cell membrane rigidity,support and stability. They can’t produce sterols so they take it from their environment. The sterol in their cell membrane helps them to mimic the cell membrane of the host cells so they can evade host immune system
•Permeability barrier
•Selective /active transport of solutes
•Site of energy generation
•Synthesis of:
DNA(this one doesn’t occur in cell membrane. Occurs in cytoplasm of bacteria cell. The rest occur in cell membrane)
•cell wall polymers
•membrane lipids
•Secretion of exoproteins and hydrolytic enzymes
Mnemonic: “PETS-DSS”
• P: Permeability barrier • E: Energy generation (Site of) • T: Transport of solutes (Selective/active) • S: Synthesis of DNA, cell wall polymers, and membrane lipids • D: DNA synthesis • S: Secretion of exoproteins and hydrolytic enzymes
Visualization:
• Imagine a busy factory (the cell wall) with different departments (PETS-DSS) handling various critical functions: • P: Security at the gate (permeability barrier) • E: Power generation plant (energy generation) • T: Delivery trucks transporting goods (transport of solutes) • S: Manufacturing units producing DNA, cell wall polymers, and membrane lipids • D: R&D department for DNA synthesis • S: Shipping department for exoproteins and hydrolytic enzymes
Which bacteria is the outer membrane found in?
What is the component of the outer membrane?
Which part of the outer membrane is toxic?
When these toxins are released, what symptoms does it cause?
Only in Gram-negative bacteria
•Has lipopolysaccharide/endotoxin
•Lipid A part is embedded in the leaflet and is toxic
•Fever
•Shock
•An effective permeability barrier with porins-The outer membrane, where LPS is located, acts as a barrier to many antibiotics and detergents.
• Contains porins, which are protein channels that allow the passage of small molecules while restricting larger, potentially harmful compounds.
What are nucleoids?
What are plasmids?
Why are plasmids so important
State the differences between nucleoid and plasmids
Single circular double stranded DNA or chromosome
•Plasmids are extra chromosomal DNA
•Carry genes for bacterial virulence factors: exotoxins, antibiotic resistance
No, nucleoids and plasmids are not the same. They are distinct entities within bacterial cells, each serving different purposes and having different characteristics.
- Definition: The nucleoid is the region within a bacterial cell where the primary genetic material, the bacterial chromosome, is located. It is not enclosed by a membrane.
-
Genetic Material:
- Composed of a single, circular double-stranded DNA molecule.
- Contains the essential genes required for the survival, growth, and reproduction of the bacterium.
-
Structure:
- Not a true nucleus, as it lacks a surrounding membrane.
- DNA is supercoiled and associated with proteins that help in packaging and managing the genetic material.
-
Function:
- Contains most of the genetic information necessary for the cell’s functions.
- Directs cellular activities, including metabolism, growth, and division.
- Definition: Plasmids are small, circular, double-stranded DNA molecules that are separate from the chromosomal DNA and can replicate independently.
-
Genetic Material:
- Contains non-essential genes that can confer advantageous traits to the bacterium, such as antibiotic resistance, virulence factors, or metabolic capabilities.
-
Structure:
- Much smaller than the chromosomal DNA.
- Can vary in number from one to several copies per cell.
-
Function:
- Provides additional genetic traits that can enhance survival under specific conditions.
- Often involved in horizontal gene transfer between bacteria through processes such as conjugation, transformation, or transduction.
-
Essential vs. Non-essential Genes:
- Nucleoid: Contains essential genes for basic cellular functions.
- Plasmid: Contains non-essential but often advantageous genes.
-
Replication:
- Nucleoid: Replicates once per cell division.
- Plasmid: Can replicate independently of the bacterial chromosome and can have multiple copies within a single cell.
-
Inheritance:
- Nucleoid: Inherited by daughter cells during cell division.
- Plasmid: Can be transferred between cells, including different species, through horizontal gene transfer mechanisms.
-
Size:
- Nucleoid: Typically much larger, encompassing the majority of the genetic information.
- Plasmid: Smaller, with fewer genes.
Understanding these differences is crucial in fields like microbiology, genetics, and biotechnology, where the manipulation of bacterial DNA can lead to significant advancements in medicine, agriculture, and industry.
What is the difference between fimbrae and pili?
Pili and fimbrae
Fimbrae are short flagella
Sex pilus have tunnels. It’s made of a protein called pilin
Bacteria that colonize Urinary tract have many fimbrae cuz urinating dislodges the bacteria so it’ll need plenty fimbrae to attach itself
•Pili or sex pili made of pilin
•Large, thick, fewer
•For bacterial sex (conjugation)
•Fimbrae –hairlike structures on bacteria
J Pili (singular: pilus) are hair-like appendages found on the surface of many bacteria. They are made of protein and are primarily involved in various forms of adhesion and interaction with the environment or other cells. Here are the key aspects of pili:
- Composition: Pili are composed of protein subunits called pilins.
- Appearance: They appear as thin, filamentous structures protruding from the bacterial cell surface.
-
Common Pili (Fimbriae):
- Function: Primarily involved in adhesion to surfaces, host tissues, and other cells. This helps bacteria colonize and form biofilms.
- Role in Pathogenicity: Important for establishing infections by attaching to host cells.
-
Sex Pili (Conjugative Pili):
- Function: Involved in the process of bacterial conjugation, where they facilitate the transfer of genetic material between bacterial cells.
- Mechanism: The sex pilus forms a bridge-like connection between two bacterial cells, allowing the transfer of plasmids, which can carry genes for antibiotic resistance, virulence factors, and other traits.
-
Adhesion:
- Pili enable bacteria to adhere to various surfaces, including host tissues, medical devices, and other bacteria. This adhesion is crucial for colonization, biofilm formation, and the establishment of infections.
-
Motility:
- Some pili, like type IV pili, are involved in a form of movement known as “twitching motility.” This allows bacteria to move across surfaces by extending and retracting pili.
-
Conjugation:
- Sex pili are essential for the process of conjugation, which is a major mechanism of horizontal gene transfer among bacteria. This process contributes to genetic diversity and the spread of antibiotic resistance genes.
-
Immune Evasion:
- By constantly changing the composition of pili (a process known as antigenic variation), bacteria can evade the host immune system, making it difficult for the host to mount an effective immune response.
- Pathogenesis: Pili are critical for the pathogenicity of many bacteria, making them important targets for the development of new antimicrobial therapies.
- Vaccines: Pili components are being explored as potential vaccine targets to prevent bacterial infections.
- Biotechnology: Understanding the mechanisms of pilus formation and function can aid in the development of new biotechnological tools and applications.
In summary, pili are versatile appendages that play crucial roles in bacterial adhesion, motility, genetic exchange, and pathogenesis. Their importance in both basic bacterial physiology and their role in infections make them significant targets for research and medical intervention.
•Small, thin, numerous
•For adherence
What are mesosomes
What is its function?
They are folded Invaginations in the cytoplasmic membrane of bacteria cells
Not all bacteria have mesosomes. Mesosomes is the site for respiratory active especially when the bacteria is undergoing budding or asexual reproduction.
•Cell division
•Site for Respiratory activity
What are ribosomes made up of ?
What’s the function of ribosomes?
Ribosomes of prokaryotes (in this case,bacteria) are bigger than that of eukaryotic cells true or false
How many s units is the large and small ribosomes in a bacteria?
What about in eukaryotes
Ribosomes
•Made of RNA and proteins
•For protein synthesis
• False. Smaller than the ribosomes of eukaryotic cells
•Bacteria ribosome is 70s(50s for large and 30s for small)
•The Eukaryotic ribosome is 80s
(40s for small and 60s for large )
For my own reading: The large and small subunits of ribosomes each play distinct and crucial roles in the process of protein synthesis, also known as translation. Here’s a breakdown of their importance and specific functions:
-
mRNA Binding:
- The small subunit is responsible for binding the messenger RNA (mRNA) that carries the genetic information from the DNA to the ribosome. In prokaryotes, the 16S rRNA within the 30S small subunit binds to a specific sequence on the mRNA called the Shine-Dalgarno sequence, which helps to position the mRNA correctly for translation. In eukaryotes, the 18S rRNA in the 40S subunit helps the ribosome recognize the 5’ cap structure of the mRNA.
-
Decoding the mRNA:
- The small subunit is essential for decoding the mRNA sequence into a sequence of amino acids. It ensures that the transfer RNA (tRNA) carrying the correct amino acid pairs with the appropriate codon on the mRNA through complementary base pairing.
-
tRNA Selection:
- The small subunit checks the accuracy of codon-anticodon pairing between the mRNA and tRNA. This proofreading step is crucial for the fidelity of protein synthesis.
-
Peptide Bond Formation:
- The large subunit is primarily responsible for catalyzing the formation of peptide bonds between amino acids. This activity is facilitated by the peptidyl transferase center, which is a ribozyme (an RNA molecule with catalytic activity) located in the 23S rRNA in prokaryotes (50S subunit) and the 28S rRNA in eukaryotes (60S subunit).
-
Exit Tunnel:
- The large subunit contains an exit tunnel through which the growing polypeptide chain is threaded as it is synthesized. This tunnel ensures that the nascent protein can emerge from the ribosome in a controlled manner.
-
Binding Sites for tRNA:
- The large subunit has three binding sites for tRNA molecules:
- A site (Aminoacyl site): Where the incoming aminoacyl-tRNA (charged tRNA) binds.
- P site (Peptidyl site): Where the tRNA carrying the growing polypeptide chain is located.
- E site (Exit site): Where the uncharged tRNA exits the ribosome after its amino acid has been added to the growing chain.
- The large subunit has three binding sites for tRNA molecules:
-
Initiation:
- The small subunit binds to the mRNA and, together with initiation factors, recruits the initiator tRNA and positions it at the start codon (AUG). Once this complex is formed, the large subunit joins to form the complete ribosome, ready to begin elongation.
-
Elongation:
- During elongation, the ribosome moves along the mRNA, decoding the message and synthesizing the polypeptide. The small subunit ensures correct tRNA matching, while the large subunit catalyzes peptide bond formation and provides the structural framework for tRNA movement.
-
Termination:
- When a stop codon is reached, release factors bind to the ribosome, prompting the large subunit to cleave the completed polypeptide from the tRNA in the P site and disassemble the ribosomal complex.
- Accuracy and Efficiency: The division of tasks between the small and large subunits ensures that translation is both accurate and efficient. The small subunit’s role in mRNA binding and decoding minimizes errors in protein synthesis, while the large subunit’s catalytic activity drives the formation of the polypeptide chain.
- Regulation: Each subunit plays a role in the regulation of translation, including interactions with various factors that control the initiation, elongation, and termination phases.
In summary, the small and large ribosomal subunits are essential for the precise and efficient synthesis of proteins. Their coordinated actions ensure that genetic information encoded in mRNA is accurately translated into functional proteins.
Bacteriostatic deugs target 50s and 30s of bacteria ribosomes. These drugs don’t kill the bacteria but they stop it from growing or producing its proteins
These are the inclusions for bacteria:
Varies for different species
Has accumulated food reserves
Glycogen
Poly phosphates
Sulphur globules
Not all bacteria cells will have the above inclusions
True or false e
True
True.
The statement is accurate. Bacterial inclusions vary among species and serve as storage depots for nutrients or metabolic by-products. Not all bacterial cells will contain the same inclusions. For example:
- Glycogen: A polymer of glucose used as an energy reserve.
- Polyphosphates: Inorganic phosphate reserves.
- Sulfur globules: Stored by bacteria that oxidize sulfur compounds as an energy source.
The presence and type of inclusions depend on the species and environmental conditions, so not all bacteria will have these inclusions.
Under cell appendages, glycocalyx is made up of polysaccharides,proteins or both and has two layers. Name them.
Which of the layers is firm on the cell envelope or wall and which is loose
Most bacteria have a polysaccharide capsule. Which bacteria has a protein capsule?
Glycocalyx
•Usually made of
polysaccharides
•Capsule layer is firm on the cell envelope
•Slime layer is loose
Structure**:
- Capsule: Thick, well-organized, and firmly attached to the cell wall.
- Slime Layer: Thinner, loosely attached, and less organized.
Composition:
- Composed of polysaccharides, proteins, or both.
•Bacillus anthracis has a protein capsule- (D- Glutamate )
What are the functions of the glycocalyx
Which part of the glycocalyx protects the bacteria from being phagocytosed
Which part of the glycocalyx prevents dessication of bacteria
Which part of the glycocalyx protects the bacteria from environmental stress and anti microbial treatment
Protect against phagocytosis
•May help in adhering bacteria to tissue
•Allow bacteria to grow in biofilm-The slime layer of the glycocalyx is the part that allows bacteria to grow in a biofilm. This extracellular matrix is composed of polysaccharides and proteins and facilitates the adherence of bacteria to surfaces and to each other. It helps form a protective and adhesive layer, contributing to the biofilm’s structural integrity and its ability to resist environmental stresses and antimicrobial treatments. It also Provides a barrier against desiccation (drying out)
•Prevent nutrient loss
•Prevent water loss
•Used as antigens in certain vaccines (pneumococcus, meningococcus, H influenzae)
The capsule of the glycocalyx prevents bacteria from being phagocytosed by:
- Reducing adherence to phagocytes
- Blocking recognition by immune cells
- Inhibiting phagocyte activation
This helps bacteria evade the immune system.
What is the flagella used for?
What type of flagella do spirochetes have?
Name the bacteria that have their flagella running through their body or is inside the organism
Bacteria with no flagella are called?
Bacteria with a Tuft of flagella on one side of the bacteria are called?
Bacteria with a Tuft of flagella on both sides of the bacteria are called?
Bacteria with Flagella scattered all around cell wall is called?
Bacteria with one flagellum on one side are called?
Bacteria with flagella inside the organism or runs within body are called?
Flagella
•For motility of bacteria
• rotate to propel bacteria
Periplasmic flagella in spirochetes
•E.g. Treponema species
Types:
1.Bacteria with no flagella, atrichous
2.Tuft of flagella on one side of the bacteria-lophotrichous( lopho means tuft)
3.On both sides, it’s amphitrichous (amphi means both or on both sides)
4.Flagella scattered all around cell wall is peritrichous(peri means around or surrounding and trichous means hair). Example is E. coli
5.one flagellum on one side -monotrichous
5.Periplasmic flagella or endoflagella - flagella is inside the organism or runs within body. Treponema species is the only one with this
Flagellum- single
Flagella-many
What are bacteria endospores?
Why are endospores important
State two bacteria species that produce endospores
Endospores for hibernation in conditions that aren’t favorable
Small dehydrated and dormant forms of bacteria
•Produced in response to nutrient limitation or adverse condition
•Withstand heat, freezing, chemicals, radiation, drying etc
•Clostridium spp
•Bacillus spp
15
who developed the Gram staining technique?
Explain the procedure of gram staining
Which bacteria type stains purple after gram staining and why?
Which stains red and why?
Which part of the bacteria does the gram staining stain?
a Danish bacteriologist-Sir Christian Hans Christian Joachim Gram
Procedure: Iodine solution fixes crystal violet dye and it’s fixed for 30 seconds
Violet or purple after staining is gram positive. The timhickee the cell wall, the more the bacteria is able to retain the violet dye. That’s why gram positive has purple colour after staining
Redish or pink after staining is gram negative cuz the cell wall is thin and it can’t retain the purple dye after washing with acetone but it rather retains the safranine dye.
The dye stains the cell wall not the cell membrane.
Procedure**:
- Crystal Violet Staining: Bacterial cells are stained with crystal violet dye. For thirty seconds
- Iodine Treatment: The cells are treated with iodine, which forms a complex with the crystal violet dye. For thirty seconds
- Decolorization: The cells are then washed with alcohol or acetone. Gram-positive cells retain the crystal violet-iodine complex, while Gram-negative cells do not.
- Counterstaining: A counterstain, typically safranin, is applied for thirty seconds. This stains the Gram-negative cells pink or red, while Gram-positive cells remain purple
Crystal Violet-Iodine Complex: When Gram-negative bacteria are subjected to the Gram stain procedure, they initially take up the crystal violet dye, forming a crystal violet-iodine complex.
3. Decolorization: During the decolorization step with alcohol or acetone, the outer membrane of Gram-negative bacteria becomes more permeable, allowing the crystal violet-iodine complex to leak out. The thin peptidoglycan layer cannot retain the dye, and the bacteria lose the crystal violet color
The gram staining dye stains the cell membrane not the cell wall.
True or false
What is periplasmic membrane
False
The dye stains the cell wall not the cell membrane.
The periplasmic space is a compartment found in Gram-negative bacteria, situated between the inner and outer membranes of the cell wall. It contains a gel-like substance called the periplasm, which houses various proteins, nutrients, enzymes, and transport proteins. This space plays crucial roles in protecting the cell from external stresses, such as antibiotics, and in processes like nutrient uptake, detoxification, and signal transduction. It is a dynamic region essential for the survival and function of Gram-negative bacteria.
Which bacteria have high lipid content
Why are mycobacterium gran positive?
Acid Fast bacteria (Mycobacteria)
•Have high lipid content
Carbol fuchsin test for mycobacteria. Mycobacteria are gram positive.
•Have mycolic acids bound to the thick peptidoglycan layer
•mycolic acids Derived from Gram-positive cell envelope
•They resist decolorization )cuz of the waxy layer comprised of mycolic acids) stained hence they are gram positive
They have a slightly thinner peptidoglycan layer compared to other gram pos
Which bacteria’s shape is pleomorphic
Why is the shape pleomorphic
Which doesn’t have a cell wall or peptidoglycan ?
Mycoplasma(they are sort of gram negative)
•Have no cell wall or peptidoglycan
•Their cell membranes are stabilized by sterols
•Cell wall antibiotics don’t work on
mycoplasma
•Shape is pleomorphic-Lack of cell wall helps mycoplasma to have a pleomorphic shape
Spirochetes(exmaple is treponema species) cannot be effectively gram stained. What about them makes it difficult to gram stain them?
-
Which of the following bacteria is typically difficult to visualize using the Gram stain due to its thin and delicate structure?
- A) Escherichia coli
- B) Staphylococcus aureus
- C) Treponema pallidum
- D) Bacillus anthracis
- **
-
What is the primary reason spirochetes are not well-visualized with a traditional Gram stain?
- A) Lack of a cell wall
- B) Presence of a thick peptidoglycan layer
- C) They are very thin and do not retain the stain well
- D) They have a capsule that repels the stain
- **Answer:
-
Which of the following is a common method used to visualize spirochetes in the laboratory?
- A) Gram staining
- B) Dark-field microscopy
- C) Acid-fast staining
- D) Endospore staining
- *
-
Spirochetes such as Treponema pallidum can be visualized using which of the following specialized staining techniques?
- A) Methylene blue staining
- B) Silver staining
- C) India ink staining
- D) Crystal violet staining
-
Fluorescent antibody techniques are particularly useful for identifying which type of bacteria that are difficult to visualize with standard staining methods?
- A) Mycobacterium
- B) Clostridium
- C) Spirochetes
- D) Enterobacter
-
Which of the following techniques is often used in conjunction with dark-field microscopy to enhance the detection of spirochetes in clinical samples?
- A) Giemsa staining
- B) Immunofluorescence
- C) Capsule staining
- D) Acid-fast staining
- **
-
Why might silver staining be preferred over Gram staining for detecting spirochetes in tissue samples?
- A) Silver staining specifically binds to spore-forming bacteria.
- B) Silver staining can visualize the delicate and thin structure of spirochetes.
- C) Silver staining is faster and easier to perform.
- D) Silver staining only detects bacteria in the exponential growth phase.
- **
Here are two more challenging MCQs focused on techniques for identifying spirochetes:
-
Which advanced molecular technique is most suitable for identifying spirochetes in a sample when traditional microscopic methods fail to provide a definitive diagnosis?
- A) Polymerase Chain Reaction (PCR)
- B) Gram staining
- C) Ziehl-Neelsen staining
- D) Mass spectrometry
- **
-
In diagnosing Lyme disease caused by Borrelia burgdorferi, which combination of tests is often used to confirm the presence of the spirochete when direct observation is not feasible?
- A) Dark-field microscopy and Giemsa staining
- B) Western blot and enzyme-linked immunosorbent assay (ELISA)
- C) Acid-fast staining and India ink preparation
- D) Silver staining and endospore staining
- **
-
Which of the following best explains why spirochetes such as Treponema pallidum are difficult to visualize with standard staining techniques, necessitating the use of more advanced methods like dark-field microscopy?
- A) They possess a thick polysaccharide capsule that prevents stain penetration.
- B) Their tightly coiled helical structure scatters light in a way that reduces contrast.
- C) They have a high lipid content in their cell wall that repels stains.
- D) Their motility interferes with the staining process.
- **
-
Which staining method is most appropriate for detecting spirochetes within a clinical sample where the pathogen load is expected to be extremely low?
- A) Gram stain
- B) Crystal violet stain
- C) Immunohistochemistry with spirochete-specific antibodies
- D) Endospore stain
- **
-
Why might the use of dark-field microscopy be favored over traditional light microscopy for the observation of spirochetes in clinical samples, particularly in diagnosing syphilis?
- A) Dark-field microscopy enhances the visibility of the motility of spirochetes.
- B) It allows for the differentiation of spirochetes from other spiral-shaped bacteria.
- C) It selectively stains spirochetes while excluding other bacterial forms.
- D) It can visualize spirochetes directly in stained blood smears.
- **
Spirochetes
•Cannot be Gram stained. Why? Spirochetes are difficult to stain due to their helical shape and due to their thin, flexible structure and unique cell wall composition, which includes lipids and lacks a rigid peptidoglycan layer. These factors hinder the uptake and retention of traditional stains used for bacteria. Specialized staining techniques and methods, such as silver staining or fluorescent antibody techniques, are often necessary for successful visualization and identification of spirochetes in laboratory settings.
•Very thin
•Dark field microscopy/ other methods
Spirochetes example is treponema species. Antigen or antibody test is preferred in hospitals cuz t’s difficult to grow these species and staining to detect the organism too is difficult
Here are five MCQs based on the information provided:
-
Which of the following bacteria is typically difficult to visualize using the Gram stain due to its thin and delicate structure?
- A) Escherichia coli
- B) Staphylococcus aureus
- C) Treponema pallidum
- D) Bacillus anthracis
- Answer: C) Treponema pallidum
-
What is the primary reason spirochetes are not well-visualized with a traditional Gram stain?
- A) Lack of a cell wall
- B) Presence of a thick peptidoglycan layer
- C) They are very thin and do not retain the stain well
- D) They have a capsule that repels the stain
- Answer: C) They are very thin and do not retain the stain well
-
Which of the following is a common method used to visualize spirochetes in the laboratory?
- A) Gram staining
- B) Dark-field microscopy
- C) Acid-fast staining
- D) Endospore staining
- Answer: B) Dark-field microscopy
-
Spirochetes such as Treponema pallidum can be visualized using which of the following specialized staining techniques?
- A) Methylene blue staining
- B) Silver staining
- C) India ink staining
- D) Crystal violet staining
- Answer: B) Silver staining
-
Fluorescent antibody techniques are particularly useful for identifying which type of bacteria that are difficult to visualize with standard staining methods?
- A) Mycobacterium
- B) Clostridium
- C) Spirochetes
- D) Enterobacter
- Answer: C) Spirochetes
Here are two more MCQs focused on techniques for identifying spirochetes:
-
Which of the following techniques is often used in conjunction with dark-field microscopy to enhance the detection of spirochetes in clinical samples?
- A) Giemsa staining
- B) Immunofluorescence
- C) Capsule staining
- D) Acid-fast staining
- Answer: B) Immunofluorescence
-
Why might silver staining be preferred over Gram staining for detecting spirochetes in tissue samples?
- A) Silver staining specifically binds to spore-forming bacteria.
- B) Silver staining can visualize the delicate and thin structure of spirochetes.
- C) Silver staining is faster and easier to perform.
- D) Silver staining only detects bacteria in the exponential growth phase.
- Answer: B) Silver staining can visualize the delicate and thin structure of spirochetes.
Here are two more challenging MCQs focused on techniques for identifying spirochetes:
-
Which advanced molecular technique is most suitable for identifying spirochetes in a sample when traditional microscopic methods fail to provide a definitive diagnosis?
- A) Polymerase Chain Reaction (PCR)
- B) Gram staining
- C) Ziehl-Neelsen staining
- D) Mass spectrometry
- Answer: A) Polymerase Chain Reaction (PCR)
-
In diagnosing Lyme disease caused by Borrelia burgdorferi, which combination of tests is often used to confirm the presence of the spirochete when direct observation is not feasible?
- A) Dark-field microscopy and Giemsa staining
- B) Western blot and enzyme-linked immunosorbent assay (ELISA)
- C) Acid-fast staining and India ink preparation
- D) Silver staining and endospore staining
- Answer: B) Western blot and enzyme-linked immunosorbent assay (ELISA)
Here are three more challenging MCQs based on spirochetes and the techniques for their identification:
-
Which of the following best explains why spirochetes such as Treponema pallidum are difficult to visualize with standard staining techniques, necessitating the use of more advanced methods like dark-field microscopy?
- A) They possess a thick polysaccharide capsule that prevents stain penetration.
- B) Their tightly coiled helical structure scatters light in a way that reduces contrast.
- C) They have a high lipid content in their cell wall that repels stains.
- D) Their motility interferes with the staining process.
- Answer: B) Their tightly coiled helical structure scatters light in a way that reduces contrast.
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Which staining method is most appropriate for detecting spirochetes within a clinical sample where the pathogen load is expected to be extremely low?
- A) Gram stain
- B) Crystal violet stain
- C) Immunohistochemistry with spirochete-specific antibodies
- D) Endospore stain
- Answer: C) Immunohistochemistry with spirochete-specific antibodies
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Why might the use of dark-field microscopy be favored over traditional light microscopy for the observation of spirochetes in clinical samples, particularly in diagnosing syphilis?
- A) Dark-field microscopy enhances the visibility of the motility of spirochetes.
- B) It allows for the differentiation of spirochetes from other spiral-shaped bacteria.
- C) It selectively stains spirochetes while excluding other bacterial forms.
- D) It can visualize spirochetes directly in stained blood smears.
- Answer: A) Dark-field microscopy enhances the visibility of the motility of spirochetes.
Which type of bacteria cannot be gram stained
Since gram staining doesn’t work, what other methods can be used to view them?
Spirochetes
•Cannot be Gram stained
•Very thin
•Dark field microscopy/ other methods
Spirochetes example is treponema species. Antigen or antibody test is preferred in hospitals cuz t’s difficult to grow these species and staining to detect the organism too is difficult
Bacteria are classified into genus and species. So for salmonella enterica, salmonella is the genus and the species is salmonella enterica
State the different classification of bacteria
Shape/morphology
•Cell wall structure / staining properties
•Oxygen growth requirements
•Based on Temperature requirements
•Based on pH
•Based on antigenic properties etc.
State the different shapes of bacteria with examples for each
Questions will be like what is the shape of this bacteria? or what bacteria is this?
Look at the picture on bacteria shapes again
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Coccus (plural: cocci): Spherical or round-shaped bacteria.
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Examples:
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Staphylococci: These bacteria occur in clusters resembling grapes.(like a ball of clothes. Or clusters of balls)
- Example: Staphylococcus aureus (causes skin infections, pneumonia, and other infections)
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Streptococci: These bacteria cocci occur in chains or pairs.
- Example: Streptococcus pneumoniae (causes pneumonia and other respiratory infections)
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Diplococci: These bacteria occur in pairs or two two.
- Example: Neisseria gonorrhoeae (causes gonorrhea)
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Staphylococci: These bacteria occur in clusters resembling grapes.(like a ball of clothes. Or clusters of balls)
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Examples:
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Bacillus (plural: bacilli): Rod-shaped or chain shaped bacteria.
-
Examples:
- Escherichia coli: Commonly found in the intestines of humans and animals.
- Bacillus anthracis: Causes anthrax, primarily affecting herbivorous mammals but can infect humans.
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Listeria monocytogenes: Causes listeriosis, a foodborne illness.
-salmonella typhi(flagellate rods shaped or bacilli shaped)
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Examples:
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Spirillum (plural: spirilla): Spiral-shaped bacteria with a rigid helical shape.
-
Example:
-
Campylobacter jejuni: A common cause of foodborne illness and gastroenteritis.
-H pylori (if you see is it rod shaped or spiral shaped, choose spiral. If you see rod but no spiral, choose rod)
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Campylobacter jejuni: A common cause of foodborne illness and gastroenteritis.
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Example:
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Spirochete: Spiral-shaped bacteria with a flexible helical shape.
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Example:
- Treponema pallidum: Causes syphilis, a sexually transmitted infection.
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Example:
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Vibrio: Curved or comma-shaped bacteria
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Example:
- **Vibrio cholerae(with one flagellum) Causes cholera, a diarrheal disease transmitted through contaminated water and food.
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Example:
-
Filamentous: Long, thin, and thread-like bacteria.
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Example:
- Actinomyces israelii: Associated with infections in humans, particularly in the mouth and throat.
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Example:
- Spore formers:clostridium and bacillus (cereus and anthracis)
State the different groupings of bacteria according to their antigenic properties and
Based on carbohydrate or protein antigens from bacteria cell wall
Eg. Grouping streptococcus
Glycolipids or carb lipids are some of the antigenic structures the Bactria has.
•Based on capsular polysaccharide
e.g Streptococcus pneumoniae
Certainly! Bacteria can be classified based on different types of antigens present on their surface. Here are two common approaches based on antigenic properties:
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Capsular Polysaccharides:
- Many pathogenic bacteria produce a polysaccharide capsule surrounding their cell wall. This capsule is often antigenic and plays a crucial role in virulence by protecting the bacteria from host immune defenses.
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Serotyping: Serotyping based on capsular polysaccharides involves identifying and classifying bacteria into different serotypes or serogroups based on variations in their capsule antigens.
- Example: Streptococcus pneumoniae can be serotyped based on the composition of its polysaccharide capsule, which helps in vaccine development and epidemiological studies.
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Protein or Carbohydrate Antigens:
- Bacteria also express other surface antigens, such as proteins or carbohydrate moieties, which can be antigenic and are recognized by the host immune system.
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Antibody-Based Typing: Antibodies specific to these surface antigens can be used to differentiate between bacterial strains or species.
- Example: Antibodies against specific protein antigens on the surface of Neisseria meningitidis can help differentiate between different serogroups of this pathogen.
These classification methods based on capsular polysaccharides, proteins, or carbohydrate antigens are essential for understanding bacterial diversity, pathogenicity, and epidemiology. They are particularly important in vaccine development, as they help target specific antigens that can induce protective immune responses against bacterial infections.
The common method used to group strept by its antigenic properties is what?
What does this method involve?
Which type of bacteria classified using the hemolysis on blood agar classification classified using the above method
How are bacteria classified using the hemolysis on blood agar classification?
Which of the types causes greenish or brownish discoloration around colonies?
Which of the types creates a clear zone around colonies?
Which doesn’t create any color change around colonies?
Streptococci are classified into different groups based on their antigenic properties, specifically the carbohydrate antigens present in their cell wall. The most common method used for this classification is serological typing, which involves identifying and grouping streptococci based on the Lancefield antigen grouping system.
The Lancefield system categorizes streptococci into groups based on the specific carbohydrate antigen found in their cell wall. The major groups identified by this system are:
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Group A Streptococcus (GAS): These streptococci have the Lancefield group A antigen, which consists of a carbohydrate antigen called the M protein.
- Example: Streptococcus pyogenes, which causes a wide range of infections including strep throat, scarlet fever, and invasive infections like necrotizing fasciitis.
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Group B Streptococcus (GBS): These streptococci have the Lancefield group B antigen.
- Example: Streptococcus agalactiae, a common cause of neonatal sepsis and meningitis.
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Group C Streptococcus (GCS): These streptococci have the Lancefield group C antigen.
- Example: Streptococcus equi subsp. equi, which causes strangles in horses, and Streptococcus dysgalactiae subsp. equisimilis, which can cause human infections ranging from mild skin infections to more severe invasive diseases.
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Group D Streptococcus (GDS): This group includes a heterogeneous collection of streptococci that have the Lancefield group D antigen.
- Example: Enterococcus faecalis and Enterococcus faecium, which are important opportunistic pathogens in hospital-acquired infections.
- Other Groups: There are also Lancefield groups F, G, H, and others, which include various streptococcal species.
These groupings are important for epidemiological studies, diagnosis, and treatment decisions, as different groups of streptococci may exhibit different pathogenic potentials and require different approaches for management and prevention.
The Lancefield classification and hemolysis on blood agar are two different methods for identifying and categorizing streptococci and other bacteria. Here’s how they differ:
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Lancefield Classification:
- Basis: This system classifies beta-hemolytic streptococci based on the carbohydrate composition of antigens present on the bacterial cell wall.
- Groups: It divides beta-hemolytic streptococci into different groups labeled A, B, C, D, etc. For example, Streptococcus pyogenes is Group A, and Streptococcus agalactiae is Group B.
- Use: Primarily used for beta-hemolytic streptococci to identify different species and understand their pathogenic potential.
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Hemolysis on Blood Agar:
- Basis: This method categorizes bacteria based on their ability to lyse red blood cells and the pattern of hemolysis observed on blood agar plates.
-
Types:
- Alpha-hemolysis: Partial breakdown of red blood cells, resulting in a green or brownish discoloration around colonies (e.g., Streptococcus pneumoniae).
- Beta-hemolysis: Complete breakdown of red blood cells, creating a clear zone around colonies (e.g., Streptococcus pyogenes).
- Gamma-hemolysis: No breakdown of red blood cells, with no color change around colonies (e.g., Enterococcus faecalis).
- Use: Provides a preliminary classification based on the hemolytic pattern and helps differentiate between different types of streptococci and other bacteria.
In summary, the Lancefield classification identifies streptococci based on specific cell wall antigens, while hemolysis on blood agar provides a preliminary classification based on the bacterium’s ability to lyse red blood cells. Both methods are used together to comprehensively identify and classify bacterial species.
explain how strept is grouped by its hemolytic properties
In addition to the Lancefield antigen grouping system, streptococci are also classified based on their hemolytic properties when grown on blood agar plates. This classification helps distinguish between different species and strains based on their ability to lyse red blood cells, resulting in different patterns of hemolysis:
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Alpha-Hemolysis:
- Description: Alpha-hemolytic streptococci partially lyse red blood cells, causing a greenish discoloration of the agar around the bacterial colonies due to the partial breakdown of hemoglobin.
- Example: Streptococcus pneumoniae (a member of the viridans group of streptococci).
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Beta-Hemolysis:
- Description: Beta-hemolytic streptococci completely lyse red blood cells, resulting in a clear zone or “beta-hemolysis” around the colonies on blood agar plates.
- Example: Streptococcus pyogenes (Group A streptococcus), which produces streptolysin O and S, toxins that cause complete hemolysis.
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Gamma-Hemolysis:
- Description: Gamma-hemolytic streptococci do not produce hemolysis and do not alter the appearance of blood agar around the bacterial colonies.
- Example: Enterococcus spp. and some non-hemolytic streptococci.
In summary, streptococci are classified into groups (such as Group A, B, C, etc.) based on the Lancefield antigen system, which identifies specific carbohydrate antigens on their cell walls. Additionally, their hemolytic properties on blood agar plates—alpha, beta, or gamma hemolysis—further distinguish different species and help in their identification and classification in clinical microbiology.
Explain classification of bacteria based on temperature and give an example each
Minimum temperature for growth, psychrophiles,
Some moderate temp is mesophiles
High temp is thermophiles
Very high temp, hyperthermophiles
H Classification of bacteria based on their growth temperature is an important aspect of microbiology and helps categorize bacteria into different groups based on their optimal temperature requirements for growth. Bacteria are broadly categorized into three groups based on their temperature preferences:
-
Psychrophiles:
- Optimal Growth Temperature: Below 20°C
- Description: Psychrophiles are bacteria that thrive in cold temperatures and are typically found in polar regions or cold environments.
- Example: Psychrobacter spp., which are commonly found in cold marine environments and food storage facilities.
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Mesophiles:
- Optimal Growth Temperature: 20-45°C
- Description: Mesophiles are bacteria that grow best at moderate temperatures, similar to those found in the human body.
- Example: Escherichia coli, a common inhabitant of the human intestines and a mesophile that grows optimally at body temperature (37°C).
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Thermophiles:
- Optimal Growth Temperature: Above 45°C
- Description: Thermophiles are bacteria that thrive in high temperatures, such as those found in hot springs, compost piles, or deep-sea hydrothermal vents.
- Example: Thermus aquaticus, which is notable for its heat-resistant DNA polymerase enzyme used in the polymerase chain reaction (PCR) technique. It thrives in hot springs with temperatures around 70-75°C.
Explain classification of bacteria based on ph and give an example each
Check the proper ph range for each
Optimum pH is 7.2 -7.6
•Acidophiles do well under acidic conditions eg
lactobacilli. Lactobacilli mainly colonized vagina. This is what usually makes vagina acidic.
•Some tolerate alkaline conditions -alkaliphiles
eg Vibrio cholerae
Neutrophiles:
These bacteria grow best at neutral pH
Most of the bacteria grow at neutral pH.
Example: E. coli
Explain classification of bacteria based on oxygen requirements and give an example each
Strict/Obligate aerobes: grow only in the presence of oxygen. Example is mycobacterium tuberculosis
•Strict /obligate anaerobe: bacteria grow in the absence of oxygen. Example is clostridium tetani
Most bacteria are facultative anaerobes
•Facultative anaerobe: can Grow in the presence or absence of oxygen. Example is E. coli
•Most bacteria of medical importance belong to this group
•Microaerophilic bacteria grow best in the presence of low oxygen tension
Example is campylobacter jejuni
Type of polysaccharide making up the glycocalyx
The glycocalyx of bacteria consists of two main types of polysaccharides:
-
Capsular Polysaccharides:
- Form a tightly bound, organized layer around the bacterial cell.
- Provide protection against desiccation and host immune responses.
- Example: Streptococcus pneumoniae uses its polysaccharide capsule to evade immune detection and cause infections.
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Slime Layer (S-layer):
- A looser, diffuse layer of polysaccharides and glycoproteins.
- Facilitates adherence to surfaces and biofilm formation.
- Example: Staphylococcus epidermidis utilizes a slime layer for biofilm formation on medical devices, contributing to infection.
These glycocalyx structures are crucial for bacterial survival, adaptation to environments, and interactions with hosts. They play significant roles in bacterial virulence and pathogenicity by aiding in attachment to surfaces, evasion of host defenses, and forming protective biofilms.
Types of polysaccharides making up the glycocalyx
Which bacteria forms biofilms on medical devices
Sure, here’s a summary of the types of polysaccharides making up the glycocalyx in bacteria:
-
Capsular Polysaccharides:
- Form a tightly bound, organized layer around the bacterial cell.
- Firmly attached to the cell wall.
- Important for virulence, protecting the bacterium from phagocytosis and immune responses.
- Example: Streptococcus pneumoniae uses its polysaccharide capsule to evade the immune system and cause infections like pneumonia.
-
Slime Layer (S-layer):
- Looser, diffuse layer of polysaccharides and glycoproteins surrounding the bacterial cell.
- More loosely attached than capsules and can be easily washed off.
- Helps bacteria adhere to surfaces and protect against desiccation. In an MCQ scenario, if asked specifically about which part of the glycocalyx protects against desiccation, the capsule would generally be the best answer. This is because the capsule is more effective at retaining moisture due to its dense and tightly bound structure compared to the slime layer.
So, you should pick capsule unless the question explicitly specifies the slime layer or focuses on loosely structured protection.
- Facilitates biofilm formation, aiding in bacterial aggregation and surface adherence.
- Example: Staphylococcus epidermidis produces a slime layer, contributing to its ability to form biofilms on medical devices and cause infections.
These glycocalyx structures are important for bacterial survival, virulence, and adaptation to various environments. They play roles in adherence to surfaces, protection against host immune responses, and biofilm formation, which are crucial factors in bacterial pathogenicity and infection.
Culture medium isn’t very necessary.
What are the two main ways that gene transfer occurs in bacteria
Vertical or Horizontal
Explain vertical gene transfer
Does it cause mixing of genetic traits?
Vertical transfer occurs from parents to offsprings may include any genetic mutations acquired by the parent
It occurs from parents to offsprings during reproduction
Generational Inheritance: The term “vertical” is used because the transfer of genetic information occurs from one generation to the next in a linear, or vertical, manner. The genetic material is passed “down” from parents to offspring, maintaining a vertical lineage
•Daughter cells have identical genetic material
Vertical gene transfer is like from mother to child. Top to down.
This is asexual reproduction of the bacterium where it’s dna duplicates and it undergoes both karyokinesis (duplication of nucleus) and cytokinesis(duplication of cytoplasm)
The nucleus gets divided into two daughter nuclei. The cytoplasm, cell organelles and the nuclei divide and are passed on to two daughter cells equally.
Vertical gene transfer is a fundamental process in natural reproduction, where the offspring inherit half of their genetic material from each parent, resulting in a mix of genetic traits from both this is for in humans.
In bacteria, In bacteria, vertical gene transfer does not typically involve the mixing of genetic traits from different sources, as it occurs through binary fission, where a single bacterial cell replicates its DNA and divides into two identical daughter cells.
For the mixing of genetic traits (recombination) in bacteria, horizontal gene transfer is the key mechanism. Horizontal gene transfer involves the transfer of genetic material between bacteria, leading to the mixing of genetic traits from different cells.
This is in contrast to horizontal gene transfer, which occurs when genetic material is transferred between organisms in the same generation, a process more common in bacteria and other microorganisms.
Explain horizontal gene transfer
Acquired DNa by horizontal gene transfer is integrated by?
Horizontal gene transfer/lateral gene transfer
•bacteria transfers genetic material to another organism that is not its offspring
•The acquired DNA is integrated by homologous recombination
Horizontal gene transfer (HGT) refers to the process by which genetic material is transferred between different organisms that are not directly parent and offspring. In other words, it involves the movement of genetic material (such as genes or DNA segments) between unrelated or distantly related organisms within the same generation
