Lecture 13 Flashcards
Why is the ability to adhere significant for bacteria in many environments?
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.
What are some examples of bacterial adherence to host cells and tissues?
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.
Give examples of bacterial adherence to food sources.
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.
What are the two main types of glycocalyces found in bacteria?
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.
What is the significance of bacterial adherence to abiotic surfaces?
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.
What is a glycocalyx in bacteria?
A glycocalyx in bacteria is a polysaccharide layer that surrounds the cell. It contributes to bacterial adherence and provides protection to the cell.
How does the glycocalyx contribute to adherence in bacteria?
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.
What is the relationship between glycocalyces and biofilms?
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.
How does a slime layer differ from a capsule?
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.
What is a bacterial capsule?
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.
How are capsules typically attached to the bacterial cell surface?
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.
Are capsules required for bacterial growth in the lab?
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.
What is the role of bacterial capsules in protection?
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.
How do capsular polysaccharides vary in structure between bacterial strains and species?
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.
How are bacterial capsules visualized in the laboratory?
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.
Describe the typical size range of strands in capsular polysaccharides.
Strands in capsular polysaccharides typically range from 1 to 100 kilodaltons (kDa) in size. These strands consist of multiple repeating sugar subunits.
How does the capsule function as a nutrient source?
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.
What is the similarity between capsular polysaccharides and LPS O-antigen?
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.
How many capsular serotypes of E. coli are known, and what is an example of an E. coli capsular polysaccharide?
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.
Why are capsular polysaccharides important for bacterial strains?
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.
What protective functions does the capsule serve against environmental factors?
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.
What role does the capsule play in reducing the efficacy of antibiotics and antimicrobial peptides?
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.
What is the significance of the capsule’s adherence function?
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.
How can the capsule’s functions impact bacterial survival and pathogenicity?
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
