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MICR 221 > Lecture 10 > Flashcards

Lecture 10 Flashcards

1
Q

Question: How is bacterial susceptibility to an antibiotic measured?

A

Answer: Bacterial susceptibility to an antibiotic is measured by the minimum inhibitory concentration (MIC), which is the lowest concentration of the antibiotic that fully inhibits bacterial growth.

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2
Q

Question: What is the difference between E. coli and S. aureus in terms of Gram staining?

A

Answer: E. coli is Gram-negative, while S. aureus is Gram-positive.

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3
Q

Question: What impact does cell wall structure have on antibiotic susceptibility?

A

Answer: Cell wall structure has a major impact on antibiotic susceptibility. Differences in cell wall structure, such as between Gram-negative and Gram-positive bacteria, can affect how antibiotics interact with and penetrate the bacterial cell.

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4
Q

Question: Which type of bacteria generally have a thicker peptidoglycan layer in their cell wall?

A

Answer: Gram-positive bacteria, such as S. aureus, generally have a thicker peptidoglycan layer in their cell wall compared to Gram-negative bacteria like E. coli.

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5
Q

Question: How might differences in cell wall structure influence MIC values between Gram-negative and Gram-positive bacteria?

A

Answer: Due to differences in cell wall structure, Gram-negative bacteria like E. coli may have higher MIC values for certain antibiotics compared to Gram-positive bacteria like S. aureus.

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6
Q

Question: What additional structure do Gram-negative bacteria have outside of the peptidoglycan layer?

A

Answer: Gram-negative bacteria have an outer membrane outside of the peptidoglycan layer.

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7
Q

Question: What is the function of the outer membrane in Gram-negative bacteria?

A

Answer: The outer membrane serves as an additional protective barrier for Gram-negative bacteria, contributing to their resistance to certain antibiotics and other environmental stresses.

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7
Q

Question: What is the composition of the outer membrane in Gram-negative bacteria?

A

Answer: The outer membrane of Gram-negative bacteria is composed of a lipid bilayer.

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8
Q

Question: How does the presence of an outer membrane affect the susceptibility of Gram-negative bacteria to antibiotics?

A

Answer: The outer membrane of Gram-negative bacteria can limit the penetration of certain antibiotics, making them less susceptible to some antibiotics compared to Gram-positive bacteria. This structural difference contributes to the variations in minimum inhibitory concentration (MIC) values observed between Gram-negative and Gram-positive bacteria.

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9
Q

Question: What is the composition of the outer leaflet of the Gram-negative outer membrane?

A

Answer: The outer leaflet of the Gram-negative outer membrane is composed of lipopolysaccharides (LPS).

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10
Q

Question: What is the composition of the inner leaflet of the Gram-negative outer membrane?

A

Answer: The inner leaflet of the Gram-negative outer membrane is composed of phospholipids.

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11
Q

Question: Which type of bacteria contain lipopolysaccharides (LPS) in their outer membrane?

A

Answer: Lipopolysaccharides (LPS) are exclusively found in the outer membrane of Gram-negative bacteria.

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12
Q

Question: What is the function of the outer membrane in Gram-negative bacteria?

A

Answer: The outer membrane serves as an impermeable barrier, excluding antibiotics, host defenses, and other molecules from entering the bacterial cell.

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13
Q

Question: Why are membrane proteins important in the Gram-negative outer membrane?

A

Answer: Membrane proteins are essential for various functions, including transport of molecules, detecting stimuli from the environment, and facilitating communication between the bacterial cell and its surroundings.

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14
Q

Question: What are the chemical properties of lipopolysaccharide (LPS) that contribute to its barrier function?

A

Answer: Lipopolysaccharide (LPS) has several chemical properties that contribute to its barrier function, including being negatively charged, amphipathic (having both hydrophilic and hydrophobic regions), and sterically bulky.

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15
Q

Question: What are the three main parts of lipopolysaccharide (LPS)?

A

Answer: Lipopolysaccharide (LPS) consists of three main parts: Lipid A, core polysaccharides, and O-antigen.

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16
Q

Question: What is the function of Lipid A in lipopolysaccharide (LPS)?

A

Answer: Lipid A anchors the LPS molecule to the outer membrane of Gram-negative bacteria and is responsible for its endotoxic properties.

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16
Q

Question: What is the function of O-antigen in lipopolysaccharide (LPS)?

A

Answer: O-antigen, also known as O-specific polysaccharide, is the outermost part of the LPS molecule and contributes to the antigenic diversity of Gram-negative bacteria.

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17
Q

Question: What role do core polysaccharides play in lipopolysaccharide (LPS)?

A

Answer: Core polysaccharides provide structural stability to the LPS molecule and help to connect Lipid A to the O-antigen.

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18
Q

Question: How is Lipid A positioned in the Gram-negative outer membrane?

A

Answer: Lipid A is embedded in the outer membrane of Gram-negative bacteria, anchoring the lipopolysaccharide (LPS) molecule to the membrane.

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19
Q

Question: What is the chemical composition of Lipid A?

A

Answer: Lipid A consists of glucosamine sugars attached to fatty acids, typically containing phosphorylated groups which contribute to its negatively charged nature.

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20
Q

Question: What is the role of Lipid A in the toxicity of LPS?

A

Answer: Lipid A is responsible for the toxicity of LPS, also known as ENDOTOXIN. It triggers an immune response when released from lysed bacterial cells, leading to fever, inflammation, and potentially severe complications such as septic shock and multiple organ failure.

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21
Q

Question: What happens when cells containing Lipid A are lysed?

A

Answer: When cells containing Lipid A are lysed, the Lipid A is released into the surrounding environment, where it can trigger immune responses and cause adverse effects.

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22
Q

Question: What are some of the consequences of Lipid A-induced toxicity?

A

Answer: Lipid A-induced toxicity can lead to fever, inflammation, and in severe cases, septic shock and multiple organ failure, making it a critical component in the pathogenesis of Gram-negative bacterial infections.

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23
Q

Question: What is the role of the core polysaccharide in lipopolysaccharide (LPS)?

A

Answer: The core polysaccharide links lipid A to the O-antigen portion of lipopolysaccharide (LPS), providing structural integrity to the LPS molecule.

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24
Q

Question: What is the chemical composition of the core polysaccharide?

A

Answer: The core polysaccharide is made of sugars, typically containing branched structures. It includes Kdo (2-keto-3-deoxyoctulosonate), an anionic sugar that contributes to its negatively charged nature.

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25
Q

Question: What is the significance of Kdo in the core polysaccharide?

A

Answer: Kdo (2-keto-3-deoxyoctulosonate) is an important component of the core polysaccharide. It is an anionic sugar that is phosphorylated, contributing to the overall negative charge of the LPS molecule.

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26
Q

Question: What role does the core polysaccharide play in the recognition of Gram-negative bacteria by the immune system?

A

Answer: The core polysaccharide, along with Lipid A and O-antigen, is recognized by the immune system as a pathogen-associated molecular pattern (PAMP), triggering immune responses against Gram-negative bacterial infections.

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26
Q

Question: How does the core polysaccharide contribute to the overall structure of LPS?

A

Answer: The core polysaccharide forms the backbone of the LPS molecule, linking the lipid A portion to the O-antigen portion and providing stability to the entire LPS structure.

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27
Q

Question: What is the composition of the O-antigen portion of lipopolysaccharide (LPS)?

A

Answer: The O-antigen portion of LPS is composed of repeating 3-5 sugar units, with the number of repeats varying among bacterial strains.

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28
Q

Question: How does the size of LPS vary among bacterial strains?

A

Answer: The size of LPS can vary among bacterial strains due to differences in the number of repeating sugar units in the O-antigen portion.

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29
Q

Question: How does the structure of LPS vary between bacterial strains?

A

Answer: The structure of LPS can vary between bacterial strains, particularly in the composition and arrangement of the O-antigen portion, which is used for bacterial classification.

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30
Q

Question: What is an example of bacterial classification based on the O-antigen portion of LPS?

A

Answer: E. coli O157:H7 is an example where “O157” refers to the type of O-antigen present in the LPS of this strain.

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31
Q

Question: Why is the O-antigen portion of LPS considered antigenic?

A

Answer: The O-antigen portion of LPS is recognized by the immune system as an antigen, triggering immune responses such as the production of antibodies against specific bacterial strains.

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32
Q

Question: How do bacteria use variation in the O-antigen portion of LPS to evade the immune response?

A

Answer: Bacteria can change the structure of the O-antigen portion of LPS to avoid detection by the immune system, making it more difficult for antibodies to recognize and neutralize the bacteria.

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32
Q

Question: What role do divalent cations such as Ca2+ and Mg2+ play in stabilizing the outer membrane of Gram-negative bacteria?

A

Answer: Divalent cations stabilize the outer membrane by cross-bridging adjacent lipopolysaccharide (LPS) molecules, neutralizing electrostatic repulsion between negatively charged components such as phosphates and Kdo sugars.

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33
Q

Question: How do divalent cations counteract the negative charges present in the outer membrane?

A

Answer: Divalent cations neutralize the negative charges in the outer membrane, reducing the repulsion between LPS molecules and contributing to the stability of the membrane.

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34
Q

Question: What is the primary function of the outer membrane in Gram-negative bacteria?

A

Answer: The outer membrane acts as a permeability barrier, preventing toxic substances from reaching internal targets within the bacterial cell.

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35
Q

Question: What is the consequence of removing divalent cations from the outer membrane?

A

Answer: Removing divalent cations weakens the stability of the outer membrane, making it more susceptible to disruption.

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36
Q

Question: How can molecules like EDTA affect the stability of the outer membrane?

A

Answer: Chelating agents such as EDTA bind divalent cations, effectively removing them from the outer membrane and weakening its stability.

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37
Q

Question: Why is the stability of the outer membrane important for Gram-negative bacteria?

A

Answer: The stability of the outer membrane is crucial for maintaining the structural integrity of Gram-negative bacteria, protecting them from environmental stresses and contributing to their survival and pathogenicity.

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38
Q

Question: How does the outer membrane achieve its function as a permeability barrier?

A

Answer: The outer membrane consists of steric bulk, hydrophilic, and hydrophobic regions that substances must pass through, thereby regulating the entry of molecules into the bacterial cell.

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39
Q

Question: What types of substances are prevented from reaching internal targets by the outer membrane?

A

Answer: The outer membrane prevents toxic substances, such as antibiotics, detergents, and host immune factors, from reaching internal targets within the bacterial cell.

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40
Q

Question: What are the three main components of the outer membrane?

A

Answer: The outer membrane consists of the O-antigen, core polysaccharide, and Lipid A. These components contribute to its structure and function as a permeability barrier.

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41
Q

Question: Why is the outer membrane an essential component of Gram-negative bacteria?

A

Answer: The outer membrane is crucial for the survival and pathogenicity of Gram-negative bacteria, as it provides protection against environmental stresses and regulates the entry of molecules into the bacterial cell.

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42
Q

Question: What components of the outer membrane restrict the passage of hydrophobic antibiotics?

A

Answer: The charged lipid A, core polysaccharide, and divalent cations in the outer membrane of Gram-negative bacteria limit the passage of hydrophobic antibiotics.

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43
Q

Question: How do hydrophobic antibiotics interact with the outer membrane and cytoplasmic membrane of Gram-negative bacteria?

A

Answer: Hydrophobic antibiotics can easily cross the cytoplasmic membrane of Gram-negative bacteria but face more limited passage through the outer membrane due to the charged lipid A, core, and divalent cations, which restrict their entry.

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44
Q

Question: What type of antibiotics are more susceptible to being restricted by the outer membrane of Gram-negative bacteria?

A

Answer: Hydrophobic antibiotics may face more restrictions in passing through the outer membrane of Gram-negative bacteria due to the hydrophilic nature of the O-antigen and core polysaccharide.

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45
Q

Question: How does the outer membrane contribute to the susceptibility of Gram-negative bacteria to antibiotics compared to Gram-positive bacteria?

A

Answer: Gram-positive bacteria are generally more susceptible to many antibiotics compared to Gram-negative bacteria, partly due to the outer membrane acting as an additional barrier that limits the entry of antibiotics, particularly hydrophilic ones.

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46
Q

Question: What protective role does the outer membrane play against degradative enzymes?

A

Answer: The outer membrane of Gram-negative bacteria protects against degradative enzymes such as proteases and lipases, which may be present in environments like the gastrointestinal tract.

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47
Q

Question: Why are enteric bacteria typically Gram-negative?

A

Answer: Enteric bacteria are typically Gram-negative because the outer membrane provides them with additional protection against degradative enzymes and other environmental stresses encountered in the gastrointestinal tract.

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48
Q

Question: How does the outer membrane protect against the action of lysozyme from the innate immune system?

A

Answer: The outer membrane acts as a barrier against lysozyme, which is an enzyme of the innate immune system. Lysozyme and other enzymes are generally too large to penetrate the outer membrane.

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49
Q

Question: Why are most enzymes unable to degrade the outer membrane itself?

A

Answer: The outer membrane of Gram-negative bacteria is resistant to degradation by most enzymes due to its structure and composition, which provide protection against enzymatic attack.

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50
Q

Question: How does the protective function of the outer membrane contribute to the survival and pathogenicity of Gram-negative bacteria?

A

Answer: The protective function of the outer membrane enables Gram-negative bacteria to survive in hostile environments, evade the host immune response, and colonize host tissues, contributing to their pathogenicity.

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51
Q

Question: What are some characteristics of detergents?

A

Answer: Detergents are amphipathic molecules, often negatively charged, with hydrophilic and hydrophobic regions.

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52
Q

Question: How do detergents affect lipid bilayers?

A

Answer: Detergents solubilize lipid bilayers by disrupting their structure and breaking down the hydrophobic interactions between lipid molecules.

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53
Q

Question: What role does lipopolysaccharide (LPS) play in protecting the outer membrane from detergents?

A

Answer: Lipopolysaccharide (LPS) in the outer membrane acts as a barrier that keeps detergents away from the hydrophobic core of the membrane through steric effects, hydrophilicity, and charge repulsion.

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53
Q

Question: How does the outer membrane of Gram-negative bacteria respond to detergents compared to the cytoplasmic membrane?

A

Answer: While the cytoplasmic membrane is easily solubilized by detergents, the outer membrane of Gram-negative bacteria is resistant to detergents.

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54
Q

Question: How does the protective function of the outer membrane against detergents contribute to the survival of Gram-negative bacteria?

A

Answer: The outer membrane’s resistance to detergents, such as bile acids in the gut, helps protect Gram-negative bacteria from environmental stresses and contributes to their survival and colonization in host tissues.

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55
Q

Question: How does the presence of sufficient Mg2+ affect the formation of lipid A in LPS?

A

Answer: If Mg2+ is present in sufficient amounts, LPS is made with a “normal” lipid A structure.

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55
Q

Question: What role do divalent cations, such as Mg2+, play in the structure of lipopolysaccharide (LPS)?

A

Answer: Divalent cations, particularly Mg2+, are needed for cross-bridging within the structure of lipopolysaccharide (LPS).

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56
Q

Question: What is the role of Mg2+ in cross-bridging within LPS?

A

Answer: Mg2+ ions cross-bridge the phosphate groups present in the structure of LPS, contributing to its stability and integrity.

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57
Q

Question: How does the cross-bridging of phosphate groups by Mg2+ affect the properties of LPS?

A

Answer: Cross-bridging of phosphate groups by Mg2+ enhances the structural integrity of LPS, making it less susceptible to disruption and more resistant to environmental stresses.

58
Q

Question: Why is the presence of divalent cations important for the proper formation of LPS in Gram-negative bacteria?

A

Answer: Divalent cations, particularly Mg2+, are essential for the proper formation and stability of LPS in Gram-negative bacteria, ensuring the integrity of the outer membrane and its protective functions.

59
Q

Question: What happens to the structure of lipopolysaccharide (LPS) when Mg2+ is limited in the environment?

A

Answer: When Mg2+ is limited, some bacteria modify lipid A with 4-aminoarabinose (4AA) to compensate.

60
Q

Question: How does the modification with 4-aminoarabinose (4AA) affect the structure of LPS?

A

Answer: 4-aminoarabinose (4AA) forms cross-bridges with phosphate groups in LPS, providing an alternative mechanism for stabilizing the structure when Mg2+ is limited.

61
Q

Question: What is the purpose of forming cross-bridges between 4-aminoarabinose (4AA) and phosphate groups in LPS?

A

Answer: Cross-bridges between 4-aminoarabinose (4AA) and phosphate groups enhance the structural integrity of LPS, compensating for the absence of Mg2+ and maintaining the stability of the outer membrane.

62
Q

Question: How does the modification of lipid A with 4-aminoarabinose (4AA) impact the properties of LPS?

A

Answer: The modification with 4-aminoarabinose (4AA) allows LPS to maintain its protective functions, such as serving as a permeability barrier and protecting against environmental stresses, even when Mg2+ is limited.

63
Q

Question: Why is the ability to modify lipid A with 4-aminoarabinose (4AA) important for the survival of Gram-negative bacteria in environments with limited Mg2+?

A

Answer: The ability to modify lipid A with 4-aminoarabinose (4AA) provides Gram-negative bacteria with an adaptive mechanism to cope with Mg2+ limitation, ensuring the stability and integrity of the outer membrane and their survival in challenging environments.

64
Q

Question: What is the chemical nature of colistin?

A

Answer: Colistin is a cationic lipopeptide antibiotic.

65
Q

Question: What is the specificity of colistin in terms of bacterial targeting?

A

Answer: Colistin specifically kills Gram-negative bacteria.

66
Q

Question: How does colistin exert its antibacterial activity?

A

Answer: Colistin binds to the phosphate groups of lipid A in the outer membrane of Gram-negative bacteria.

67
Q

Question: What is the effect of colistin’s lipid tail?

A

Answer: Colistin’s lipid tail permeabilizes lipid membranes, leading to disruption of the bacterial cell membrane.

68
Q

Question: Why is colistin particularly effective against Gram-negative bacteria?

A

Answer: Colistin’s mechanism of action, which involves binding to lipid A in the outer membrane and disrupting the cell membrane, is particularly effective against Gram-negative bacteria due to their unique outer membrane structure.

69
Q

Question: How do Mg2+ levels affect the sensitivity of bacterial cells to colistin?

A

Answer: When Mg2+ levels are plentiful, bacterial cells are sensitive to colistin.

70
Q

Question: What is the role of 4-aminoarabinose (4AA) in colistin resistance?

A

Answer: 4-aminoarabinose (4AA) modification of lipid A prevents colistin from binding to lipid A, thereby preventing its antibacterial activity and conferring resistance to colistin.

71
Q

Question: How does Mg2+ limitation lead to colistin resistance?

A

Answer: When Mg2+ levels are limited, lipid A in the outer membrane may be modified with 4-aminoarabinose (4AA). This modification prevents colistin from binding to lipid A, resulting in resistance to colistin.

71
Q

Question: What happens to colistin sensitivity in bacterial cells when Mg2+ levels are limited?

A

Answer: When Mg2+ levels are limited, bacterial cells may become resistant to colistin.

72
Q

Question: How does the ability to modify lipid A with 4-aminoarabinose (4AA) impact the effectiveness of colistin as an antibiotic?

A

Answer: The ability of bacteria to modify lipid A with 4-aminoarabinose (4AA) reduces the effectiveness of colistin as an antibiotic by preventing its binding to lipid A and compromising its antibacterial activity.

73
Q

Question: What is the function of the mcr-1 (mobilized colistin resistance) gene?

A

Answer: The mcr-1 gene confers resistance to colistin, an antibiotic used to treat bacterial infections.

74
Q

Question: How does the modification of lipid A by phosphoethanolamine affect colistin sensitivity?

A

Answer: The attachment of phosphoethanolamine to lipid A by MCR-1 alters the charge of lipid A, resulting in a positive charge that repels colistin, thereby reducing its effectiveness.

74
Q

Question: How is the mcr-1 gene typically transmitted between bacterial strains?

A

Answer: The mcr-1 gene is typically plasmid-encoded, which allows for easy spread between bacterial strains via horizontal gene transfer (HGT).

75
Q

Question: What enzymatic activity does the MCR-1 protein possess?

A

Answer: The MCR-1 protein attaches phosphoethanolamine to lipid A, altering its structure and conferring resistance to colistin.

76
Q

Question: Why is the spread of the mcr-1 gene concerning for public health?

A

Answer: The spread of the mcr-1 gene via plasmids and HGT poses a significant public health concern as it can lead to the widespread dissemination of colistin-resistant bacteria, limiting treatment options for bacterial infections and potentially leading to treatment failures.

77
Q

Question: What is the composition of the outer membrane in terms of protein content?

A

Answer: The outer membrane is protein-rich, comprising approximately 50% of its mass.

78
Q

Question: What types of proteins are predominantly found in the outer membrane?

A

Answer: The outer membrane contains mostly lipoproteins and β-barrel proteins.

79
Q

Question: What are the functions of porins and receptors in the outer membrane?

A

Answer: Porins and receptors in the outer membrane are essential for the import of nutrients and other molecules into the bacterial cell.

80
Q

Question: What role do secretion systems and efflux pumps play in the outer membrane?

A

Answer: Secretion systems and efflux pumps in the outer membrane are required for the export of molecules, including toxins and waste products, out of the bacterial cell.

81
Q

Question: How do proteins contribute to building and anchoring the outer membrane?

A

Answer: Proteins in the outer membrane play a crucial role in building the structure of the membrane, interacting with lipopolysaccharides (LPS) and other components. Additionally, some proteins serve as anchors, attaching the outer membrane to the peptidoglycan layer.

82
Q

Question: What is the primary function of porins in the outer membrane?

A

Answer: Porins in the outer membrane form channels that allow nutrients to enter the bacterial cell.

83
Q

Question: What structural type do porins typically belong to?

A

Answer: Porins are β-barrel proteins.

84
Q

Question: What is the typical oligomeric state of porins?

A

Answer: Most porins are trimeric, meaning they consist of three subunits.

85
Q

Question: How many porins are present per bacterial cell, on average?

A

Answer: There are over 250,000 porins per bacterial cell, indicating their abundance and importance for nutrient uptake.

86
Q

Question: What is the structure of porins, and how does it relate to their function?

A

Answer: Porins have a water-filled channel at their center, which provides a pathway for the passage of molecules. The structure of porins also provides some selectivity, allowing only certain molecules to pass through the channel while excluding others.

87
Q

Question: Where is lipopolysaccharide (LPS) assembled?

A

Answer: LPS is assembled in the cytoplasmic membrane of Gram-negative bacteria.

88
Q

Question: What is the challenge in transporting LPS to the outer membrane?

A

Answer: LPS must cross the periplasm and the outer membrane, which is difficult due to the amphipathic nature of LPS.

89
Q

Question: What is the role of Lpt proteins in LPS transport?

A

Answer: Lpt proteins form the Lpt pathway, which is responsible for transporting LPS from the cytoplasmic membrane to the outer membrane.

90
Q

Question: Which specific protein is involved in translocating LPS through the outer membrane?

A

Answer: LptD, a β-barrel protein, is responsible for translocating LPS through the outer membrane.

91
Q

Question: How does the Lpt pathway contribute to the assembly of the outer membrane?

A

Answer: The Lpt pathway facilitates the transport of LPS molecules to the outer membrane, where they are incorporated into the structure of the membrane, contributing to its integrity and function.

92
Q

What are the consequences of the outer membrane not being attached to peptidoglycan (PG)?

A

Vesiculation and destabilization.

93
Q

What is the function of proteins that anchor the outer membrane to PG?

A

To stabilize the outer membrane.

94
Q

What is Braun’s lipoprotein?

A

A protein found in E. coli’s outer membrane. It has a fatty acid chain embedded in the outer membrane and is covalently attached to PG.

95
Q

What is the significance of Braun’s lipoprotein?

A

It is the most abundant protein in E. coli and plays a crucial role in stabilizing the outer membrane by covalently attaching to PG.

96
Q

How do some porins and lipoproteins bind to PG?

A

Non-covalently.

96
Q

What is the periplasmic region?

A

It is the space between the cytoplasmic and outer membranes in Gram-negative bacteria.

96
Q

What percentage of the cell volume does the periplasm occupy?

A

20-40% of the cell volume.

97
Q

How does the osmotic pressure affect the positioning of the cytoplasmic membrane in relation to the peptidoglycan (PG)?

A

The osmotic pressure pushes the cytoplasmic membrane against the peptidoglycan (PG).

98
Q

What proteins attach the outer membrane to the peptidoglycan (PG) in the periplasmic space?

A

Various proteins facilitate the attachment of the outer membrane to the peptidoglycan (PG) in the periplasmic space.

99
Q

What is the periplasmic space known for in terms of protein content?

A

It is a protein-rich space within the cell.

100
Q

What is the function of nutrient transport proteins in the periplasmic space?

A

Nutrient transport proteins deliver nutrients to the cytoplasmic membrane.

101
Q

Name some examples of catabolic enzymes found in the periplasmic space.

A

Examples include proteases, lipases, and other enzymes involved in the breakdown of molecules.

102
Q

Besides nutrient transport and catabolic enzymes, what other types of proteins are found in the periplasmic space?

A

Proteins in the periplasmic space can also include components of cellular structures such as pili and flagella.

103
Q

What are penicillin-binding proteins (PBPs) known for?

A

Penicillin-binding proteins are enzymes involved in cell wall synthesis and are targets for antibiotics like penicillin.

104
Q

What is the role of antibiotic resistance enzymes such as β-lactamases?

A

These enzymes confer resistance to antibiotics, particularly β-lactam antibiotics, by breaking down their molecular structure.

105
Q

Describe the structure of Gram-positive cell walls regarding the outer membrane.

A

Gram-positive cell walls lack an outer membrane.

105
Q

What is the thickness of the peptidoglycan (PG) layer in Gram-positive cell walls?

A

The peptidoglycan (PG) layer in Gram-positive cell walls is thick, ranging from 20 to 80 nanometers.

106
Q

What are teichoic acids, and where are they found?

A

Teichoic acids are negatively charged polymers found in the cell walls of Gram-positive bacteria.

107
Q

How does the periplasmic space in Gram-positive bacteria compare to that in Gram-negative bacteria?

A

Gram-positive bacteria have a smaller periplasmic space compared to Gram-negative bacteria.

108
Q

What is the approximate thickness of the peptidoglycan (PG) layer in Gram-negative bacteria?

A

In Gram-negative bacteria, the peptidoglycan (PG) layer is much thinner, typically less than 10 nanometers.

109
Q

What is the major component of Gram-positive cell walls?

A

Teichoic acids are the major component of Gram-positive cell walls.

110
Q

What is the typical length of teichoic acid polymers in Bacillus subtilis?

A

In Bacillus subtilis, teichoic acid polymers consist of 20-30 glycerol units.

110
Q

Describe the structure of teichoic acids.

A

Teichoic acids are linear polymers of glycerol or ribitol joined by phosphate groups.

110
Q

What is the approximate weight percentage of teichoic acids in the cell wall of Bacillus subtilis?

A

Teichoic acids constitute approximately 50% by weight in the cell wall of Bacillus subtilis.

110
Q

What type of charge do the phosphate groups of teichoic acids carry?

A

The phosphate groups of teichoic acids are negatively charged.

110
Q

What are some possible substituents on the glycerol or ribitol units of teichoic acids?

A

Glycerol or ribitol units of teichoic acids might have glucosamine or D-alanine substituents.

110
Q

What is the charge of the R group in the structure of teichoic acids?

A

The R group in teichoic acids is positively charged.

110
Q

What is Wall Teichoic Acid (WTA)?

A

Wall Teichoic Acid (WTA) is a type of teichoic acid that is attached to N-acetylmuramic acid (NAM) or the peptide in peptidoglycan (PG). It extends beyond the PG surface.

110
Q

What is Lipoteichoic Acid (LTA)?

A

Lipoteichoic Acid (LTA) is another type of teichoic acid. It is attached to glycolipids in the cytoplasmic membrane and is associated with peptidoglycan (PG).

110
Q

How is Wall Teichoic Acid (WTA) different from Lipoteichoic Acid (LTA) in terms of attachment?

A

WTA is attached directly to the peptidoglycan (PG) layer (to NAM), while LTA is attached to glycolipids in the cytoplasmic membrane.

111
Q

Where does Wall Teichoic Acid (WTA) extend?

A

WTA extends beyond the surface of the peptidoglycan (PG).

112
Q

What is the association of Lipoteichoic Acid (LTA) with peptidoglycan (PG)?

A

Lipoteichoic Acid (LTA) is associated with peptidoglycan (PG).

113
Q

How do teichoic acids regulate where peptidoglycan (PG) is degraded during cell division?

A

Teichoic acids play a role in regulating where peptidoglycan (PG) is degraded during cell division.

113
Q

What role do teichoic acids play in controlling access to the cell wall surface?

A

Teichoic acids regulate access to the cell wall surface.

113
Q

What is the function of teichoic acids in anchoring the cell wall to the cytoplasmic membrane?

A

Teichoic acids help anchor the cell wall to the cytoplasmic membrane.

113
Q

How do teichoic acids minimize repulsion in the cell wall?

A

Teichoic acids bind to cations, which helps minimize repulsion within the cell wall.

113
Q

How are teichoic acids recognized by the innate immune system?

A

Teichoic acids are recognized by the innate immune system as microbe-associated molecular patterns (MAMPs).

113
Q

What protective mechanism does D-alanylation provide against antibiotics and host defenses?

A

D-alanylation of teichoic acids protects against antibiotics and host defenses.

113
Q

What are some other examples of microbial components recognized by the innate immune system?

A

Other microbial components recognized by the innate immune system include lipopolysaccharides (LPS) and peptidoglycan (PG).

113
Q

How do teichoic acids contribute to pathogenesis?

A

Teichoic acids contribute to pathogenesis by facilitating adhesion, biofilm formation, and colonization of host tissues. Their release can also cause a severe inflammatory response.

114
Q

What is the significance of toll-like receptors (TLRs) in the immune response?

A

Toll-like receptors (TLRs) play a crucial role in recognizing microbial components and initiating innate immune responses.

114
Q

What staining technique is required to visualize mycobacteria?

A

Mycobacteria require acid-fast staining for visualization.

114
Q

Which receptors on immune cells are activated by microbial components like teichoic acids?

A

Pattern recognition receptors (PRRs) on immune cells, such as toll-like receptors (TLRs), are activated by microbial components like teichoic acids.

114
Q

How do mycobacteria appear in Gram staining?

A

In Gram staining, mycobacteria do not appear pink or purple as typical Gram-positive or Gram-negative bacteria do.

114
Q

Describe the procedure of acid-fast staining for mycobacteria.

A

The procedure involves heating cells with stain, followed by decolorizing with acid-alcohol. Mycobacteria retain the stain, while other cells are decolorized.

114
Q

What is a characteristic feature of mycobacteria regarding staining?

A

Mycobacteria are difficult to stain using conventional Gram-staining methods.

114
Q

What is unique about the cell walls of mycobacteria?

A

Mycobacteria have unusual cell walls compared to other bacteria.

115
Q

Despite having an outer membrane, how are mycobacteria classified in terms of Gram staining?

A

Mycobacteria are considered Gram-positive, despite having an outer membrane.

116
Q

What are some components of the arabinogalactan layer in mycobacteria?

A

The arabinogalactan layer consists of sugar polymers.

116
Q

What is the layer between the peptidoglycan (PG) and the outer membrane in mycobacteria called?

A

The layer between the peptidoglycan (PG) and the outer membrane in mycobacteria is called the arabinogalactan layer.

116
Q

What is the main component of the outer membrane of mycobacteria?

A

The outer membrane of mycobacteria is mainly composed of mycolic acids, not lipopolysaccharides (LPS) as in typical Gram-negative bacteria.

116
Q

How are mycolic acids connected to peptidoglycan (PG) in mycobacteria?

A

Mycolic acids are covalently connected to peptidoglycan (PG) in mycobacteria.

117
Q

Describe the structure of the mycobacterial outer membrane.

A

The mycobacterial outer membrane is an asymmetrical bilayer.

118
Q

What components make up the inner leaflet and outer leaflet of the mycobacterial outer membrane?

A

The inner leaflet is composed of mycolic acids, while the outer leaflet consists of glycolipids.

118
Q

What is unique about the composition of the mycobacterial outer membrane in terms of phospholipids?

A

The mycobacterial outer membrane does not contain phospholipids.

118
Q

What is required for small molecules to enter the mycobacterial cell through the outer membrane?

A

Porins are needed for small molecules to enter the mycobacterial cell through the outer membrane.

118
Q

How would you describe the nature of the mycobacterial outer membrane?

A

The mycobacterial outer membrane is very hydrophobic, making it highly impermeable.

119
Q

What consequence does the hydrophobic nature of the mycobacterial outer membrane have on antibiotic permeability?

A

The hydrophobic nature of the mycobacterial outer membrane makes it impenetrable to many antibiotics.

MICR 221 (12 decks)

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