Lecture 13 Flashcards
1
Q
Why is the ability to adhere significant for bacteria in many environments?
A
The ability to adhere is significant for bacteria in many environments because it allows them to establish stable associations with various surfaces, including food sources, host cells and tissues, and abiotic surfaces. Adherence is essential for colonization, biofilm formation, and persistence in these environments.
2
Q
What are some examples of bacterial adherence to host cells and tissues?
A
Bacterial adherence to host cells and tissues involves interactions between bacteria and the surfaces of host cells or tissues. This adherence can occur with both commensal bacteria, which coexist harmlessly with the host, and pathogenic bacteria, which cause disease. Examples include the adherence of pathogens to epithelial cells during infection.
2
Q
Give examples of bacterial adherence to food sources.
A
Bacterial adherence to food sources includes interactions such as cellulolytic microbes adhering to cellulose. Cellulose is a common component of plant-based foods, and microbes capable of breaking down cellulose adhere to it to facilitate digestion and nutrient acquisition.
3
Q
What are the two main types of glycocalyces found in bacteria?
A
The two main types of glycocalyces found in bacteria are slime layers and capsules. Slime layers are diffuse surface layers that are easily removed from the cell, while capsules are organized surface layers that are firmly attached to the cell.
3
Q
What is the significance of bacterial adherence to abiotic surfaces?
A
Bacterial adherence to abiotic surfaces, such as medical devices, is a critical factor in biofilm formation. Biofilms are structured communities of bacteria attached to surfaces and encased in a matrix of extracellular polymeric substances. Biofilms on medical devices can lead to device-associated infections, posing significant challenges in healthcare settings.
3
Q
What is a glycocalyx in bacteria?
A
A glycocalyx in bacteria is a polysaccharide layer that surrounds the cell. It contributes to bacterial adherence and provides protection to the cell.
3
Q
How does the glycocalyx contribute to adherence in bacteria?
A
The glycocalyx in bacteria contributes to adherence by allowing bacteria to adhere to various surfaces, including host cells, tissues, and abiotic surfaces. It forms a sticky layer that promotes attachment and colonization.
4
Q
What is the relationship between glycocalyces and biofilms?
A
Glycocalyces in bacteria are related to extracellular polymeric substances (EPS) in biofilms. Biofilms are structured communities of bacteria attached to surfaces and encased in a matrix of EPS, which includes polysaccharides from the glycocalyx. Glycocalyces contribute to biofilm formation by promoting bacterial adherence and providing structural support.
4
Q
How does a slime layer differ from a capsule?
A
A slime layer is a diffuse surface layer of glycocalyx that is easily removed from the bacterial cell. In contrast, a capsule is an organized surface layer of glycocalyx that is firmly attached to the cell and not easily removed.
4
Q
What is a bacterial capsule?
A
A bacterial capsule is a surface layer of polysaccharides that surrounds the bacterial cell. It forms a protective barrier and contributes to bacterial adherence and evasion of host immune responses.
4
Q
How are capsules typically attached to the bacterial cell surface?
A
Capsules are typically long polymers covalently attached to the bacterial cell surface. They can be attached to various components of the cell envelope, including lipopolysaccharides (LPS), phospholipids, and peptidoglycan.
5
Q
Are capsules required for bacterial growth in the lab?
A
Capsules are not required for bacterial growth in the laboratory. However, they are often observed in bacteria isolated from natural environments, where they provide protection against environmental stresses and facilitate interactions with other organisms.
6
Q
What is the role of bacterial capsules in protection?
A
Bacterial capsules provide protection by forming a physical barrier around the bacterial cell, shielding it from environmental stresses, desiccation, and host immune responses. Capsules also inhibit the attachment of bacteriophages and other predatory organisms.
7
Q
How do capsular polysaccharides vary in structure between bacterial strains and species?
A
Capsular polysaccharides vary in structure between bacterial strains and species due to differences in the composition of sugars, modifications, and branching patterns. Each strain or species may have a unique capsular polysaccharide structure.
8
Q
How are bacterial capsules visualized in the laboratory?
A
Bacterial capsules are visualized in the laboratory by negative staining techniques. Many stains do not bind to capsules, allowing them to appear as clear halos surrounding the stained bacterial cells when viewed under a microscope. This negative staining technique highlights the presence of the capsule.
9
Q
Describe the typical size range of strands in capsular polysaccharides.
A
Strands in capsular polysaccharides typically range from 1 to 100 kilodaltons (kDa) in size. These strands consist of multiple repeating sugar subunits.
10
Q
How does the capsule function as a nutrient source?
A
The capsule can also serve as a nutrient source for bacteria. It contains polysaccharides that can be broken down and utilized by the bacterial cell for energy and growth. In nutrient-poor environments, the breakdown of the capsule can provide essential nutrients for bacterial survival.
11
Q
What is the similarity between capsular polysaccharides and LPS O-antigen?
A
Capsular polysaccharides and LPS O-antigen are similar in that they both consist of repeating sugar subunits. However, they are distinct structures with different roles in bacterial physiology and interactions with the environment.
12
Q
How many capsular serotypes of E. coli are known, and what is an example of an E. coli capsular polysaccharide?
A
There are over 80 capsular serotypes of E. coli known. An example of an E. coli capsular polysaccharide is E. coli K5 capsular polysaccharide, which consists of approximately 250 repeats of a disaccharide subunit. It is attached to phosphatidylglycerol in the outer membrane.
13
Q
Why are capsular polysaccharides important for bacterial strains?
A
Capsular polysaccharides are important for bacterial strains as they play a crucial role in bacterial virulence, evasion of host immune responses, and adaptation to different environmental conditions. The variability in capsular polysaccharide structure contributes to the diversity of bacterial strains and their ability to cause disease.
13
Q
What protective functions does the capsule serve against environmental factors?
A
The capsule serves several protective functions against environmental factors, including:
- Protection against desiccation: The highly hydrated nature of the capsule helps retain moisture, which protects the bacterial cell from drying out.
- Prevention of engulfment by predators: The capsule prevents predators such as protozoa from engulfing the bacterial cell, aiding in the bacterium’s survival.
- Protection against bacteriophage infection: The capsule acts as a physical barrier that impedes the attachment and entry of bacteriophages, reducing the risk of viral infection.
14
Q
What role does the capsule play in reducing the efficacy of antibiotics and antimicrobial peptides?
A
The capsule reduces the efficacy of antibiotics and antimicrobial peptides by acting as a physical barrier that hinders the penetration of these agents into the bacterial cell. This reduced penetration limits the effectiveness of antibiotics and antimicrobial peptides in killing or inhibiting bacterial growth, contributing to antibiotic resistance.
15
Q
What is the significance of the capsule’s adherence function?
A
The adherence function of the capsule is significant as it allows bacteria to adhere to various surfaces, including host tissues and medical devices. Adherence promotes colonization and biofilm formation, which are critical for bacterial persistence and pathogenesis in diverse environments.
16
Q
How can the capsule’s functions impact bacterial survival and pathogenicity?
A
The capsule’s functions, including protection against environmental stresses, nutrient acquisition, and evasion of host defenses, contribute to bacterial survival and pathogenicity. By providing protection and promoting adherence, the capsule enhances the bacterium’s ability to colonize hosts, evade immune responses, and cause disease.
17
What role do capsules play as a virulence factor?
Capsules serve as a virulence factor by protecting bacteria against the host's innate immune system. They prevent complement activation, inflammation, the formation of the membrane attack complex (MAC), opsonization, and phagocytosis. This protection enhances the bacterium's ability to survive and spread in the host, contributing to the development of bacteremia, meningitis, and other invasive infections.
18
How do capsules contribute to serum resistance?
Capsules contribute to serum resistance by preventing the activation of the complement system and the formation of the membrane attack complex (MAC). Additionally, capsules inhibit opsonization, the process by which pathogens are marked for phagocytosis by immune cells. This resistance allows bacteria to survive and proliferate in the bloodstream, leading to systemic infections.
19
What were the findings of the Griffith mouse experiments regarding capsules?
The Griffith mouse experiments demonstrated the significance of capsules as a virulence factor. When encapsulated strains of bacteria were injected into mice, they caused fatal infections, whereas non-encapsulated strains did not. This experiment provided early evidence of the role of capsules in protecting bacteria against host immune defenses and contributing to virulence.
20
How do capsules contribute to the pathogenesis of diseases such as bacteremia and meningitis?
Capsules contribute to the pathogenesis of diseases such as bacteremia and meningitis by enabling bacteria to evade immune surveillance and establish systemic infections. The ability of capsules to resist complement activation, phagocytosis, and other immune responses allows bacteria to survive and proliferate in the bloodstream and invade tissues, leading to severe and potentially life-threatening infections.
21
What is the significance of capsules in the context of bacterial infections?
In the context of bacterial infections, capsules are significant because they enhance the virulence of pathogenic bacteria by providing protection against host immune responses. Capsules allow bacteria to evade detection and clearance by the immune system, promoting bacterial survival and the establishment of invasive infections. Understanding the role of capsules in virulence is essential for developing strategies to prevent and treat bacterial diseases.
22
What is opsonization, and how does it relate to the adaptive immune response?
Opsonization is the process by which pathogens are marked for phagocytosis by immune cells. Antibodies or complement proteins can bind to pathogens, making them more recognizable to phagocytes. Opsonization enhances the clearance of pathogens by the immune system.
22
How do bacterial capsules interfere with the adaptive immune response?
Bacterial capsules can interfere with the adaptive immune response by masking other antigenic components of the bacterial cell surface. This masking prevents antibodies from binding to and targeting the bacteria effectively. Additionally, some capsules are made of sugars that are common in the host, making them less immunogenic and less likely to trigger an immune response.
23
How does the adaptive immune response typically target bacteria?
The adaptive immune response often relies on antibodies to target bacteria. Antibodies can facilitate opsonization, marking bacteria for phagocytosis by immune cells, and neutralizing bacterial toxins.
24
Why are capsules major vaccine targets?
Capsules are major vaccine targets because they are accessible to the immune system and are key virulence factors for many bacterial pathogens. Targeting capsules with vaccines can effectively prevent bacterial infections by enhancing immune recognition and clearance of encapsulated bacteria.
24
What is the significance of bacterial capsules being composed of sugars common in the host?
Bacterial capsules composed of sugars common in the host, such as hyaluronic acid and sialic acid, are less likely to elicit an immune response. This similarity to host molecules can lead to immune tolerance or evasion, allowing bacteria to avoid detection and clearance by the adaptive immune system.
25
How does the masking of antigenic components by bacterial capsules impact the immune response?
The masking of antigenic components by bacterial capsules reduces the effectiveness of the adaptive immune response against the bacteria. Without access to these antigens, antibodies cannot effectively recognize and target the bacteria for clearance by immune cells. This evasion strategy allows bacteria to persist and cause chronic or recurrent infections.
26
What is the effectiveness of capsular vaccines?
Capsular vaccines are very effective in preventing bacterial infections caused by encapsulated pathogens. By targeting the bacterial capsule, these vaccines can induce protective immunity and significantly reduce the incidence of diseases such as pneumonia, meningitis, and sepsis.
27
Why are polysaccharides alone not very immunogenic in capsular vaccines?
Polysaccharides alone are not very immunogenic in capsular vaccines because they are often T-cell-independent antigens, which do not effectively stimulate a robust immune response, especially in infants and young children.
28
How are capsular polysaccharides modified to evoke an immune response in vaccines?
Capsular polysaccharides are modified to evoke an immune response in vaccines by conjugating them to immunogenic protein carriers. This conjugation enhances the immunogenicity of the polysaccharides by promoting T-cell-dependent immune responses, resulting in the production of high-affinity antibodies and long-lasting immunity.
29
What is the initial step in capsule assembly?
The initial step in capsule assembly involves the activation of sugars with a nucleoside diphosphate group. This activation process is catalyzed by enzymes such as UDP-sugar pyrophosphorylase.
30
What are conjugate vaccines, and how do they work?
Conjugate vaccines are vaccines in which capsular polysaccharides are covalently attached (conjugated) to immunogenic protein carriers. By coupling polysaccharides to protein carriers, conjugate vaccines can elicit T-cell-dependent immune responses, leading to the production of memory B cells and long-lasting antibody-mediated immunity. Conjugate vaccines have significantly improved the effectiveness of capsular vaccines, particularly in infants and young children.
31
What is the significance of transferring sugars to undecaprenyl phosphate in capsule assembly?
Transferring sugars to undecaprenyl phosphate is a critical step in capsule assembly because it allows for the synthesis of lipid-linked oligosaccharide precursors. These precursors serve as building blocks for the biosynthesis of capsular polysaccharides, which are essential for the formation of bacterial capsules.
31
What is the role of UDP-sugar pyrophosphorylase in capsule assembly?
UDP-sugar pyrophosphorylase is an enzyme that catalyzes the formation of UDP-sugar molecules, which are essential components for capsule assembly. This enzyme transfers a sugar moiety from a nucleoside diphosphate to uridine diphosphate (UDP), resulting in the formation of UDP-sugars.
32
How are sugars transferred to undecaprenyl phosphate in capsule assembly?
After activation by UDP-sugar pyrophosphorylase, the activated sugars are transferred to undecaprenyl phosphate, which serves as a lipid carrier molecule. This transfer process is facilitated by specific enzymes involved in capsule biosynthesis pathways.
33
Describe the importance of capsule assembly in bacterial pathogenesis.
Capsule assembly plays a crucial role in bacterial pathogenesis by contributing to virulence and evasion of host immune defenses. Bacterial capsules protect pathogens from phagocytosis, complement-mediated lysis, and recognition by the host immune system. Additionally, capsules can facilitate adherence to host tissues and biofilm formation, leading to colonization and persistence in the host, ultimately causing diseases such as pneumonia, meningitis, and sepsis. Understanding capsule assembly mechanisms is essential for developing strategies to target bacterial capsules and combat infectious diseases.
34
What is the significance of undecaprenol's ability to activate sugars?
Undecaprenol's ability to activate sugars by attaching a reactive pyrophosphate group is crucial for initiating the biosynthesis of various cell wall components. This activation step provides the necessary energy for subsequent enzymatic reactions involved in sugar modification and polymerization, leading to the formation of structurally diverse and functionally important cell wall molecules.
34
What role does undecaprenol play in facilitating the transport of hydrophilic sugars?
Undecaprenol helps hydrophilic sugars travel through the hydrophobic membrane bilayer by serving as a lipid carrier molecule. This allows hydrophilic sugars to be transported across the membrane to participate in various biosynthetic processes.
35
Describe the importance of undecaprenol in bacterial physiology and cell wall biosynthesis.
Undecaprenol plays a vital role in bacterial physiology and cell wall biosynthesis by facilitating the transport and activation of sugars, which are essential building blocks for cell wall components. By anchoring sugars to the membrane and activating them, undecaprenol ensures the efficient synthesis of peptidoglycan, lipopolysaccharides, teichoic acids, and other critical cell wall structures. This contributes to bacterial cell integrity, shape, and resistance to environmental stresses, making undecaprenol a key molecule in bacterial cell wall metabolism.
35
How does undecaprenol keep sugars close to the membrane and enzymes?
Undecaprenol keeps sugars close to the membrane and enzymes by anchoring them to the lipid bilayer. This localization ensures efficient access of sugars to membrane-bound enzymes involved in their modification and polymerization, facilitating the biosynthesis of complex cell wall components.
36
Apart from facilitating sugar transport, what other roles does undecaprenol play in bacterial cells?
Undecaprenol is involved in the biosynthesis of various cell wall components, including peptidoglycan, lipopolysaccharides (LPS), and teichoic acids. It serves as a precursor molecule for the synthesis of these cell wall components, contributing to cell wall integrity and function.
37
How are capsule subunits transported to the outer face of the cell membrane in Gram-positive bacteria?
Capsule subunits are transported to the outer face of the cell membrane in Gram-positive bacteria by a flippase enzyme. This enzyme facilitates the flipping of capsule subunits from the inner cytoplasmic side to the outer surface of the cell membrane.
37
What is the initial step in capsule assembly in Gram-positive bacteria?
In Gram-positive bacteria, the initial step in capsule assembly involves the assembly of subunits in the cytoplasm. These subunits are synthesized from precursor molecules within the bacterial cytoplasm.
38
How are capsule polysaccharides attached to the bacterial surface in Gram-positive bacteria?
In Gram-positive bacteria, capsule polysaccharides are attached to surface molecules such as peptidoglycan, which forms the main component of the bacterial cell wall. This attachment provides structural support and anchors the capsule to the bacterial cell surface.
38
What enzyme polymerizes capsule subunits in Gram-positive bacteria?
In Gram-positive bacteria, capsule subunits are polymerized by a polymerase enzyme. This enzyme catalyzes the polymerization of individual subunits to form longer polysaccharide chains, which constitute the capsule structure.
39
Describe the significance of capsule assembly in Gram-positive bacteria.
Capsule assembly in Gram-positive bacteria is essential for virulence and survival in various environments. The capsule provides protection against host immune defenses, enhances adherence to host tissues, and contributes to biofilm formation. Understanding the mechanisms of capsule assembly in Gram-positive bacteria is crucial for developing strategies to prevent and treat infections caused by these pathogens.
40
Describe the initial step of capsule assembly in Gram-negative bacteria using the Wzx-Wzy-dependent pathway.
In Gram-negative bacteria employing the Wzx-Wzy-dependent pathway, capsule subunits are assembled in the cytoplasm by glycosyltransferases (GTs). These enzymes catalyze the formation of capsule subunits from precursor molecules within the bacterial cytoplasm.
40
What pathway do some Gram-negative bacteria use for capsule assembly?
Some Gram-negative bacteria use the Wzx-Wzy-dependent pathway for capsule assembly. This pathway involves several sequential steps to synthesize and transport capsule polysaccharides to the bacterial cell surface.
41
What role does Wzx play in capsule assembly in Gram-negative bacteria?
Wzx acts as a flippase enzyme in capsule assembly in Gram-negative bacteria. It facilitates the flipping of capsule subunits across the cell membrane, transporting them from the inner cytoplasmic side to the outer surface of the membrane.
41
Which enzyme polymerizes capsule subunits in Gram-negative bacteria utilizing the Wzx-Wzy-dependent pathway?
In Gram-negative bacteria following the Wzx-Wzy-dependent pathway, capsule subunits are polymerized by the enzyme Wzy, which serves as a polymerase. Wzy catalyzes the polymerization of individual subunits to form longer polysaccharide chains, the main components of the capsule.
42
How are capsule polysaccharides translocated to the bacterial cell surface in Gram-negative bacteria using the Wzx-Wzy-dependent pathway?
Capsule polysaccharides synthesized and polymerized in the cytoplasm are translocated to the bacterial cell surface through the Wza channel. This channel allows for the passage of polysaccharide chains across the outer membrane, where they are incorporated onto the cell surface, contributing to capsule formation.
43
Explain the significance of the Wzx-Wzy-dependent pathway in capsule assembly for Gram-negative bacteria.
The Wzx-Wzy-dependent pathway is crucial for capsule assembly in Gram-negative bacteria as it facilitates the synthesis, transport, and incorporation of capsule polysaccharides onto the bacterial cell surface. Capsules play essential roles in bacterial virulence, immune evasion, and environmental adaptation, making the understanding of capsule assembly pathways valuable for combating bacterial infections.
44
What alternative pathway for capsule assembly exists in some Gram-negative bacteria?
Some Gram-negative bacteria utilize an alternative pathway for capsule assembly that does not involve undecaprenol. This pathway allows for the assembly of the complete polysaccharide in the cytoplasm before its translocation to the bacterial cell surface.
45
Describe the initial step of capsule assembly in Gram-negative bacteria that do not use undecaprenol.
In Gram-negative bacteria that do not use undecaprenol, the initial step of capsule assembly involves the assembly of the complete polysaccharide in the cytoplasm by glycosyltransferases (GTs). These enzymes catalyze the synthesis of the polysaccharide from precursor molecules within the bacterial cytoplasm.
46
How are the fully synthesized polysaccharides transported to the bacterial cell surface in Gram-negative bacteria without undecaprenol?
In Gram-negative bacteria lacking undecaprenol, the fully synthesized polysaccharides are transferred to a lipid molecule, such as diacylglycerol phosphate, within the cytoplasm.
The polysaccharide-lipid complex is then transported to the bacterial cell surface by an ATP-binding cassette (ABC) transporter, such as KpsM and KpsT.
47
What is the name of the pathway utilized by Gram-negative bacteria without undecaprenol for capsule assembly?
The pathway utilized by Gram-negative bacteria that do not use undecaprenol for capsule assembly is known as the ABC transporter-dependent pathway. This pathway relies on ABC transporters to facilitate the transport of polysaccharides from the cytoplasm to the bacterial cell surface.
48
Explain the significance of the ABC transporter-dependent pathway in capsule assembly for Gram-negative bacteria.
The ABC transporter-dependent pathway is significant for capsule assembly in Gram-negative bacteria as it provides an alternative mechanism for the synthesis and transport of polysaccharides to the bacterial cell surface. This pathway contributes to the formation of capsules, which play crucial roles in bacterial pathogenesis, virulence, and survival in diverse environments. Understanding this pathway is essential for developing strategies to target bacterial capsules for therapeutic intervention.
49
What is the composition of the capsule of Bacillus anthracis?
The capsule of Bacillus anthracis is composed of long polymers of D-glutamic acid, which is an amino acid. Unlike many bacterial capsules, which are made from sugars, the capsule of B. anthracis is proteinaceous in nature.
50
What role does the capsule play in the virulence of Bacillus anthracis?
The capsule of Bacillus anthracis serves as an important virulence factor, contributing significantly to the pathogenesis of anthrax. It helps the bacterium evade host immunity by interfering with complement activation and preventing phagocytosis.
51
How does the capsule of Bacillus anthracis contribute to its evasion of host immunity?
The capsule of Bacillus anthracis helps the bacterium evade host immunity by interfering with complement activation and preventing phagocytosis. Additionally, the capsule is non-immunogenic, meaning it does not trigger a strong immune response in the host.
52
What is the significance of the proteinaceous capsule of Bacillus anthracis in the context of anthrax?
The proteinaceous capsule of Bacillus anthracis is a crucial virulence factor in the context of anthrax. It plays a major role in the pathogenesis of the disease by aiding the bacterium in evading host immune defenses, contributing to the severity of anthrax infections. Understanding the composition and function of the B. anthracis capsule is essential for developing effective strategies for the prevention and treatment of anthrax.
53
What are the hairlike structures found on the surface of bacteria?
The hairlike structures found on the surface of bacteria are known as pili or fimbriae. They are thin, typically less than 10 nanometers in diameter, and can be several micrometers long.
54
What are adhesins, and how are they related to pili?
Adhesins are proteins located on the surface of bacteria that enable adherence to specific receptors on host cells or other surfaces. Pili often contain adhesins, which facilitate the attachment of bacteria to host tissues or abiotic surfaces.
55
What is the primary function of pili or fimbriae in bacteria?
Pili or fimbriae in bacteria are primarily involved in adherence. They help bacteria adhere to surfaces, including host tissues and abiotic surfaces.
56
In which type of bacteria are pili or fimbriae more common?
Pili or fimbriae are more commonly found in Gram-negative bacteria. However, other types of adhesins are more prevalent in Gram-positive bacteria.
57
Describe the physical characteristics of pili or fimbriae.
Pili or fimbriae are thin, rigid structures with a diameter typically less than 10 nanometers and a length that can extend up to several micrometers. They are abundant, with many pili present per bacterial cell.
58
What are the different kinds of pili found in Gram-negative bacteria?
Gram-negative bacteria have several kinds of pili, including:
1. Type IV secretion pili (sex pili) involved in conjugation.
2. Type IV pili responsible for twitching motility.
3. Type III secretion systems.
4. Chaperone-usher (CU) pili, which are the most common type.
59
What is the function of Type IV secretion pili in Gram-negative bacteria?
Type IV secretion pili, also known as sex pili, are involved in conjugation, which is the process of transferring genetic material (such as plasmids) between bacterial cells.
60
What is the function of Type III secretion systems in Gram-negative bacteria?
Type III secretion systems in Gram-negative bacteria are specialized secretion systems used to deliver proteins directly into host cells. These systems are important for bacterial pathogenesis and virulence.
61
What is the role of Type IV pili in Gram-negative bacteria?
Type IV pili in Gram-negative bacteria are responsible for twitching motility, a form of bacterial movement that involves extension and retraction of the pili to pull the cell along surfaces.
62
Describe the structure of Chaperone-Usher (CU) Pili.
Chaperone-Usher (CU) Pili are rigid helical structures composed of thousands of major pilins. They feature a fibrillum that terminates in an adhesin, which is responsible for adherence to surfaces or host tissues. Minor pilins link the adhesin to the rod of the pilus.
63
Which type of pili is the most common in Gram-negative bacteria?
The most common type of pili in Gram-negative bacteria is the chaperone-usher (CU) pili. These pili play various roles, including adherence to host tissues and biofilm formation.
64
How are pilins incorporated into Chaperone-Usher (CU) Pili?
In the assembly of Chaperone-Usher (CU) Pili, chaperones facilitate the folding of pilins in the periplasm, and ushers assemble the pilins at the base of the pilus.
64
What is the significance of the name "Chaperone-Usher (CU) Pili"?
The name "Chaperone-Usher (CU) Pili" is derived from the mechanism of pilin assembly. Chaperones assist in folding pilins in the periplasm, while ushers are responsible for assembling the pilins at the base of the pilus.
65
What is the role of the adhesin in Chaperone-Usher (CU) Pili?
The adhesin located at the end of Chaperone-Usher (CU) Pili is responsible for adherence to surfaces or host tissues. It facilitates the initial attachment of bacteria to specific receptors, promoting colonization and biofilm formation.
66
How do Chaperone-Usher (CU) Pili contribute to bacterial virulence?
Chaperone-Usher (CU) Pili serve as virulence factors by facilitating the attachment of bacteria to host tissues and the formation of biofilms. This attachment is crucial for colonization and infection, as it prevents bacteria from being washed away by bodily fluids or mechanical forces.
67
How are the adhesin and the rod of Chaperone-Usher (CU) Pili linked?
The adhesin and the rod of Chaperone-Usher (CU) Pili are linked by minor pilins, which connect these two components of the pilus structure.
68
What are some examples of anatomical sites where CU pili-mediated attachment is important for bacterial colonization and infection?
Chaperone-Usher (CU) Pili-mediated attachment plays a significant role in bacterial colonization and infection in various anatomical sites, including the gastrointestinal (GI) tract, respiratory tract, and urinary tract.
69
How does the ability of CU pili to form biofilms contribute to bacterial virulence?
The ability of Chaperone-Usher (CU) Pili to form biofilms enhances bacterial virulence by promoting bacterial aggregation and the establishment of persistent infections. Biofilms provide bacteria with protection against host immune responses and antimicrobial agents, allowing them to thrive and persist in host environments.
70
Why is attachment to host tissues crucial for bacterial colonization and infection?
Attachment to host tissues is crucial for bacterial colonization and infection because it enables bacteria to establish a foothold in the host's body, evade clearance mechanisms, and initiate disease processes. Without attachment, bacteria may be easily expelled or eliminated by the host's immune system.
71
How do adhesins influence bacterial infections?
Adhesins play a crucial role in determining the cells and tissues to which bacteria can attach, thereby influencing the sites of bacterial infections. Different adhesins exhibit specificity for particular host cell receptors, dictating the tropism of bacteria and their ability to colonize specific anatomical sites.
71
What molecules do adhesins primarily bind to?
Adhesins primarily bind to specific molecules, often carbohydrates, on the surface of host cells or tissues.
72
How does the formation of biofilms contribute to bacterial persistence in the host?
The formation of biofilms by bacteria, facilitated by structures like Chaperone-Usher (CU) Pili, allows them to persist in host environments by providing protection against host immune responses, antibiotics, and other antimicrobial agents. Biofilms also promote bacterial aggregation and facilitate the exchange of genetic material, enhancing bacterial survival and adaptation.
73
Provide examples of bacterial species and their corresponding adhesins binding to specific host cells or tissues.
Examples include:
Streptococcus pyogenes (causing strep throat): Adhesins bind to pharyngeal epithelial cells.
Streptococcus pneumoniae: Adhesins bind to lung epithelial cells.
Uropathogenic Escherichia coli (UPEC): Adhesins bind to uroepithelial cells, contributing to urinary tract infections (UTIs).
74
How does the specificity of adhesins contribute to the pathogenesis of bacterial infections?
The specificity of adhesins in binding to particular molecules on host cells or tissues determines the tropism of bacteria and their ability to colonize specific anatomical sites. This specificity influences the initiation and progression of bacterial infections by targeting particular host tissues susceptible to bacterial adhesion and subsequent invasion.
75
Which type of pili does UPEC use to attach to proteins on uroepithelial cells?
UPEC utilizes Type I pili (T1P) to attach to proteins present on the surface of uroepithelial cells.
76
What percentage of urinary tract infections (UTIs) are caused by Uropathogenic Escherichia coli (UPEC)?
Uropathogenic Escherichia coli (UPEC) is responsible for approximately 90% of urinary tract infections (UTIs).
77
What is the significance of UPEC's ability to form intracellular bacterial communities (IBCs)?
The formation of intracellular bacterial communities (IBCs) by UPEC allows the bacteria to evade host immune responses and persist within the host.
IBCs provide a protected environment for UPEC to replicate and establish chronic or recurrent urinary tract infections. Additionally, IBCs contribute to the dissemination of UPEC within the urinary tract and may play a role in recurrent infections.
77
What type of pilus is Type I pili (T1P), and how does it contribute to UPEC infection?
Type I pili (T1P) are a type of Chaperone-Usher (CU) pilus. They facilitate the attachment of UPEC to proteins on uroepithelial cells, leading to cytoskeletal rearrangements and subsequent internalization of the bacteria. This internalization allows UPEC to form intracellular bacterial communities (IBCs) within the host cells.
78
What is the significance of UPEC's ability to ascend the ureters and enter the kidneys?
Uropathogenic Escherichia coli (UPEC) ascending the ureters and entering the kidneys can lead to upper urinary tract infections, specifically pyelonephritis, which is the inflammation of the kidney.
79
Which type of pilus does UPEC utilize to attach to glycolipids present on kidney epithelial cells?
Uropathogenic Escherichia coli (UPEC) employs P pili to attach to glycolipids on kidney epithelial cells.
80
What changes in pilus production occur in UPEC to facilitate its colonization of the upper urinary tract, including the kidneys?
To reach and colonize the upper urinary tract, particularly the kidneys, Uropathogenic Escherichia coli (UPEC) downregulates the production of Type I pili (T1P) and upregulates the production of P pili. This adjustment in pilus production enhances UPEC's ability to attach to kidney epithelial cells and establish infection in the upper urinary tract.
81
What is the significance of many copies of pilin proteins being surface-exposed?
The surface exposure of many copies of pilin proteins makes them accessible to the immune system. This accessibility enables the generation of antibodies against these proteins, which can aid in the prevention of bacterial attachment and colonization.
81
How do antibodies generated against purified adhesins contribute to preventing bacterial attachment and colonization?
Antibodies generated against purified adhesins bind to the surface-exposed pilin proteins of bacteria. This binding interferes with bacterial attachment and colonization, thus helping to prevent infections.
82
How are purified adhesins potentially useful in vaccine development?
Purified adhesins can serve as potential vaccine candidates. By generating antibodies against these adhesins, vaccines can elicit an immune response that specifically targets bacterial attachment structures, thereby preventing infections.
83
How can bacteria like Neisseria gonorrhoeae utilize antigenic variation to evade the immune system?
Bacteria like Neisseria gonorrhoeae can employ antigenic variation to evade the immune system. This process involves recombination between the pilE gene, which is actively transcribed, and other pilin genes (pilS) that are not transcribed. Through this recombination, new variants of the pilE gene are created, allowing the bacteria to alter the structure of their pili, thereby evading recognition by the immune system.
84
What is the specific role of the pilE gene in the process of antigenic variation in Neisseria gonorrhoeae?
In Neisseria gonorrhoeae, the pilE gene is actively transcribed and codes for pilin, a major component of pili. During antigenic variation, recombination events involving the pilE gene and other pilin genes (pilS) lead to the creation of new variants of the pilE gene, contributing to changes in the structure of pili.
85
How does the ability to change pilus structure through antigenic variation benefit bacteria like Neisseria gonorrhoeae?
The ability to change pilus structure through antigenic variation allows bacteria like Neisseria gonorrhoeae to evade the immune system. By altering the structure of their pili, these bacteria can avoid recognition by antibodies generated by the immune system, thereby enhancing their ability to persist and cause infections.
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What role does PapD play in the assembly of P pili?
PapD plays a crucial role in the assembly of P pili by binding to pilus subunits in the periplasm and assisting in their folding. As a chaperone component of the CU pilus system, PapD ensures that the pilus subunits achieve their correct conformation before assembly onto the growing pilus structure.
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How are P pilus subunits exported to the periplasm in bacteria?
P pilus subunits are exported to the periplasm in bacteria via the general secretion (Sec) system. This system is responsible for transporting unfolded proteins across the cytoplasmic membrane.
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What is the role of PapC in the assembly of P pili?
PapC forms the base of the pilus and is responsible for translocating pilus subunits to the bacterial surface. As part of the CU pilus system, PapC serves as the usher, facilitating the assembly of the pilus subunits into the growing pilus structure.
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Which component of the CU pilus system delivers pilus subunits to PapC during P pilus assembly?
During P pilus assembly, PapD delivers pilus subunits to PapC. PapD acts as a chaperone, ensuring that the pilus subunits are correctly folded before they are translocated to PapC for assembly onto the pilus structure.
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What is the role of PapA in the assembly of P pili?
PapA, as the major pilin protein, plays a crucial role in P pilus assembly. It is translocated by PapC and added to the base of the growing pilus structure. Mutants lacking PapA are unable to produce pili, although they still exhibit adherence properties.
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How does the role of PapA differ from that of PapC in P pilus assembly?
In P pilus assembly, PapC serves as the base and translocates pilus subunits to the bacterial surface, while PapA, as the major pilin protein, is added to the base of the growing pilus structure. PapA contributes to the structural integrity of the pilus, whereas PapC facilitates the translocation and assembly process.
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What is the function of PapH in P pilus assembly?
PapH serves to keep the pilus attached to the bacterial cell and regulates pilus length. It blocks the addition of PapA subunits to the pilus structure. Mutants lacking PapH produce long pili that are not properly attached to the cell.
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How does PapH affect the length of P pili?
The length of P pili is determined by the levels of both PapA and PapH. PapH regulates pilus length by blocking the addition of PapA subunits. Therefore, the balance between PapA and PapH levels influences the length of the pili. Overproduction of PapH results in shorter pili, while insufficient levels may lead to longer pili.
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What are the main functions of pili in Gram-positive bacteria?
The main functions of pili in Gram-positive bacteria include adhesion to surfaces, facilitating biofilm formation, and potentially mediating interactions with other cells or surfaces in the environment.
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What are some characteristics of pili in Gram-positive bacteria?
Pili in Gram-positive bacteria are long (often greater than 3 μm), thin (approximately 1 nm), and flexible. Their subunits are covalently attached together and are anchored to the peptidoglycan layer of the cell wall. Adhesins are typically attached to the ends of these pili.
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How are subunits of pili in Gram-positive bacteria transported across the membrane?
The subunits of pili in Gram-positive bacteria are transported across the membrane by the general secretion (Sec) system.
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What characteristic motif is present in pilus subunits to facilitate their assembly in Gram-positive bacteria?
Pilus subunits in Gram-positive bacteria contain the LPXTG motif, which is recognized by the enzyme sortase. Sortase cleaves this motif and forms a complex with the pilus subunit, facilitating its assembly into the pilus structure.
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What role do pilus-specific sortases play in the assembly of Gram-positive pili?
Pilus-specific sortases are responsible for forming polymers of pilus subunits in the assembly of Gram-positive pili. They create covalent bonds between the subunits, providing mechanical strength to the pilus structure.
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How is the assembled pilus incorporated into the peptidoglycan layer in Gram-positive bacteria?
The assembled pilus, along with lipid II, is transferred to peptidoglycan (PG) by housekeeping sortase. Lipid II, which includes the pilus structure, is then incorporated into the peptidoglycan layer by penicillin-binding proteins (PBPs).
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