Lecture 9 Flashcards
1
Q
Question: What is the primary target of β-lactam antibiotics?
A
Answer: The bacterial cell wall.
2
Q
Question: What are some roles of the prokaryotic cell envelope?
A
Answer: Its roles include controlling what enters and exits the cell, protecting against stresses, antibiotics, immune cells, and other external factors.
2
Q
Question: What structures make up the prokaryotic cell envelope?
A
Answer: The cytoplasmic membrane and all layers that surround it, including the cell wall, peptidoglycan, outer membrane (in Gram-negatives), and other layers outside the cell wall such as the capsule.
3
Q
Question: What are the main components of the cytoplasmic membrane?
A
Answer: The cytoplasmic membrane consists of a lipid bilayer and proteins.
4
Q
Question: What are the primary components of bacterial cytoplasmic membranes?
A
Answer: Bacterial cytoplasmic membranes are mainly composed of phospholipids.
4
Q
Question: What is the primary function of the cytoplasmic membrane?
A
Answer: The cytoplasmic membrane serves as a semipermeable barrier, allowing water and very hydrophobic substances to diffuse through while restricting the diffusion of hydrophilic substances such as ions and most nutrients.
5
Q
Question: How does the lipid composition of the cytoplasmic membrane vary depending on conditions?
A
Answer: The lipid composition of the cytoplasmic membrane varies depending on conditions such as temperature.
6
Q
Question: How are fatty acids attached to glycerol in bacterial cytoplasmic membranes?
A
Answer: Fatty acids are attached to glycerol by ester bonds.
7
Q
Question: Describe the structure of glycerol in bacterial cytoplasmic membranes.
A
Answer: Glycerol is bonded to a phosphate group, which may have substituents like ethanolamine.
8
Q
Question: What is the amphipathic nature of phospholipids in bacterial cytoplasmic membranes?
A
Answer: Phospholipids are amphipathic, meaning they have both polar and non-polar regions.
8
Q
Question: What are the functions of transporters in the bacterial cytoplasmic membrane?
A
Answer: Transporters facilitate the import of substances such as nutrients, the export of substances like extracellular polysaccharides (EPS) for biofilms and toxins, signal transduction to detect external stimuli, and energy transduction.
9
Q
Question: How do enzymes in the electron transport chain (ETC) contribute to the bacterial cytoplasmic membrane’s function?
A
Answer: Enzymes in the ETC generate a proton gradient across the membrane, known as the proton motive force (PMF), which powers ATP synthesis, transport processes, and other cellular activities.
10
Q
Question: What is the source of energy for ATP synthesis and transport processes in the bacterial cytoplasmic membrane?
A
Answer: The proton motive force (PMF) generated by the electron transport chain (ETC) enzymes serves as the energy source for ATP synthesis and transport processes.
11
Q
Question: Describe the typical environment for bacteria in terms of tonicity.
A
Answer: Bacteria are usually in a hypotonic environment, where there are more solutes inside the cell than outside.
12
Q
Question: What effect does a hypotonic environment have on bacterial cells?
A
Answer: In a hypotonic environment, water is drawn into the bacterial cell, leading to swelling. This influx of water can potentially cause osmotic lysis.
13
Q
Question: What is the main component of the cell wall in most bacteria?
A
Answer: Peptidoglycan (PG) is the major component of the cell wall in most bacteria.
14
Q
Question: How do bacteria survive in hypotonic conditions?
A
Answer: Bacteria survive in hypotonic conditions through various mechanisms such as regulating osmotic pressure through osmoregulation, modifying cell wall composition, and employing specialized transport systems to expel excess water.
15
Q
Question: What is the relationship between osmolarity and the cytoplasmic membrane?
A
Answer: Osmolarity refers to the concentration of solutes in a solution, and the cytoplasmic membrane plays a crucial role in maintaining osmotic balance within bacterial cells by regulating the movement of water and solutes across the membrane.
16
Q
Question: What is the function of the cell wall in bacteria?
A
Answer: The cell wall provides structural support and protection to the bacterial cell, helping it maintain its shape and resist osmotic pressure.
16
Q
Question: What is an additional layer found in the cell walls of Gram-negative bacteria?
A
Answer: Gram-negative bacteria have an outer membrane in addition to their peptidoglycan layer.
17
Q
Question: How do the cell walls of Gram-positive and Gram-negative bacteria differ in thickness?
A
Answer: Gram-positive bacteria have thick cell walls, while Gram-negative bacteria have thin cell walls.
18
Q
Question: How does the peptidoglycan layer respond to osmotic pressure changes?
A
Answer: The peptidoglycan layer is elastic and can stretch or contract in response to changes in osmotic pressure, helping to maintain the integrity and shape of the bacterial cell.
18
Q
Question: What role does the peptidoglycan layer play in bacterial cells?
A
Answer: The peptidoglycan layer provides strength to the cell wall, determines the shape of the bacterium, and protects against osmotic lysis by resisting the inward pressure exerted by the cytoplasm.
19
Q
Question: Why is the elasticity of the peptidoglycan layer important for bacterial cells?
A
Answer: The elasticity of the peptidoglycan layer allows bacterial cells to adapt to changes in their environment, particularly in response to fluctuations in osmotic pressure, helping them to avoid osmotic damage and maintain their structural integrity.
19
Question: What is the porosity of the peptidoglycan layer?
Answer: The peptidoglycan layer is porous and mesh-like, allowing nutrients and waste to pass through it.
19
Question: What happens to bacterial cells if the peptidoglycan (PG) layer is disrupted?
Answer: Bacterial cells become more susceptible to osmotic lysis, particularly in a hypotonic environment.
20
Question: What are some factors that target the peptidoglycan (PG) layer?
Answer: The peptidoglycan (PG) layer is targeted by antibiotics and the immune system.
21
Question: What happens to spheroplasts or protoplasts if they are moved to a hypotonic environment?
Answer: Spheroplasts or protoplasts swell and eventually lyse if they are moved to a hypotonic environment.
21
Question: Can bacteria survive peptidoglycan (PG) degradation in isotonic conditions?
Answer: Yes, bacteria can survive peptidoglycan (PG) degradation in isotonic conditions, but they may lose their shape and form spheroplasts (Gram-negative) or protoplasts (Gram-positive).
22
Question: Why is the peptidoglycan (PG) layer important for osmotic stabilization of bacterial cells?
Answer: The peptidoglycan (PG) layer provides structural support to bacterial cells and helps them resist osmotic pressure changes, thereby preventing osmotic lysis.
22
Question: How would you describe the size of Mycoplasmas?
Answer: Mycoplasmas are small, typically around 0.2 micrometers, and they exhibit pleomorphism, meaning they can vary in shape.
23
Question: What distinguishes Mycoplasmas from many other bacteria?
Answer: Mycoplasmas lack a cell wall, which is a characteristic feature that sets them apart from most other bacteria.
24
Question: How do Mycoplasmas compensate for the absence of a cell wall?
Answer: Mycoplasmas incorporate sterols from their host cells into their cytoplasmic membrane, which increases membrane stability and helps them withstand osmotic pressure differences.
25
Question: What is the typical osmotic environment inside other cells where intracellular parasites like Mycoplasmas reside?
Answer: The osmotic environment inside other cells, where intracellular parasites like Mycoplasmas reside, is typically near isotonic, providing a relatively stable environment for these organisms.
25
Question: Why are Mycoplasmas osmotically sensitive?
Answer: Mycoplasmas lack a cell wall, making them osmotically sensitive to changes in their environment.
26
Question: Why is peptidoglycan (PG) a prime target for antibiotics?
Answer: Peptidoglycan (PG) is a common component of bacterial cell walls and is absent in human cells, making it an excellent target for antibiotics to specifically attack bacterial cells without harming human cells.
27
Question: Name some antibiotics that target peptidoglycan (PG).
Answer: Antibiotics such as β-lactams (e.g., penicillins) and vancomycin are known to target peptidoglycan (PG) in bacterial cell walls.
28
Question: How does vancomycin act on peptidoglycan (PG)?
Answer: Vancomycin binds to the terminal D-Ala-D-Ala residues of peptidoglycan precursors, preventing their incorporation into the growing peptidoglycan chain, thus inhibiting cell wall synthesis and leading to bacterial cell death.
28
Question: How do antibiotics target peptidoglycan (PG)?
Answer: Antibiotics target peptidoglycan (PG) either by directly binding to its chemical structure or by inhibiting the enzymes responsible for synthesizing PG in bacterial cells.
29
Question: Why are β-lactam antibiotics effective against bacteria?
Answer: β-lactam antibiotics, like penicillins, work by interfering with the formation of peptidoglycan cross-links in bacterial cell walls, weakening the cell wall and leading to bacterial cell lysis.
30
Question: What are the primary components of peptidoglycan (PG)?
Answer: Peptidoglycan (PG) is made of sugars and amino acids.
31
Question: What is the significance of the peptide chains in peptidoglycan (PG)?
Answer: Every NAM molecule in the peptidoglycan (PG) backbone bears a peptide chain, which forms peptide cross-links with neighboring glycan strands, providing strength and stability to the cell wall.
31
Question: Describe the structure of the peptidoglycan (PG) backbone.
Answer: The PG backbone is a long glycan strand composed of repeating disaccharide units.
32
Question: What are NAM and NAG in peptidoglycan (PG)?
Answer: NAM stands for N-acetylmuramic acid, while NAG stands for N-acetylglucosamine. These are the two sugar molecules present in the disaccharide units of the PG backbone.
33
Question: How are glycan strands connected to each other in peptidoglycan (PG)?
Answer: Glycan strands are connected to each other through peptide cross-links formed by the peptide chains attached to NAM molecules.
34
Question: What is the key precursor for peptidoglycan (PG) synthesis?
Answer: Lipid II is the key precursor for peptidoglycan (PG) synthesis.
35
Question: What does Lipid II contain?
Answer: Lipid II contains a "monomeric" PG subunit, which consists of a NAM-NAG disaccharide and a pentapeptide.
36
Question: How is Lipid II anchored to the bacterial membrane?
Answer: Lipid II is bound to the bacterial membrane by undecaprenol, a lipid carrier molecule.
37
Question: What initiates the synthesis of Lipid II?
Answer: The synthesis of Lipid II begins with UDP-NAG (uridine diphosphate N-acetylglucosamine), which activates NAG, one of the sugar moieties in the NAM-NAG disaccharide.
38
Question: Where is Lipid II assembled during peptidoglycan (PG) synthesis?
Answer: Lipid II is assembled in the cytoplasm of the bacterial cell.
38
Question: Why is Lipid II important in peptidoglycan (PG) synthesis?
Answer: Lipid II serves as the precursor molecule for the addition of NAM-NAG disaccharide units and pentapeptides during peptidoglycan (PG) synthesis, playing a crucial role in building the bacterial cell wall.
39
Question: What is the composition of Lipid II?
Answer: Lipid II contains D-alanine.
40
Question: Which enzyme is responsible for making D-alanine?
Answer: Alanine racemase makes D-Ala.
41
Question: What is the function of D-Ala-D-Ala ligase?
Answer: D-Ala-D-Ala ligase synthesizes D-Ala-D-Ala.
42
Question: How does cycloserine affect the synthesis of D-alanine?
Answer: Cycloserine inhibits both alanine racemase and D-Ala-D-Ala ligase.
43
Question: How is D-alanine synthesized and incorporated in bacterial cell wall synthesis?
Answer: D-alanine is synthesized by alanine racemase and incorporated into D-Ala-D-Ala by D-Ala-D-Ala ligase, which is crucial for bacterial cell wall synthesis.
44
Question: Where are Penicillin-Binding Proteins (PBPs) located?
Answer: PBPs are located in the periplasm of bacterial cells.
45
Question: What is the role of Penicillin-Binding Proteins (PBPs) in bacterial cells?
Answer: PBPs are essential for cell growth, cell division, and cell wall recycling in bacteria.
46
Question: What is the function of the glycosyltransferase domain found in many PBPs?
Answer: The glycosyltransferase domain of PBPs synthesizes the glycan strand of peptidoglycan.
47
Question: What is the function of the transpeptidase domain found in many PBPs?
Answer: The transpeptidase domain of PBPs catalyzes the formation of peptide cross-links in peptidoglycan.
48
Question: What role does Penicillin-Binding Protein (PBP) play in peptidoglycan synthesis?
Answer: PBP adds the lipid II disaccharide to the glycan backbone of peptidoglycan.
48
Question: How is Lipid II incorporated into peptidoglycan?
Answer: Lipid II is incorporated into peptidoglycan by Penicillin-Binding Proteins (PBPs).
49
Question: What is the effect of PBP on the glycan backbone of peptidoglycan?
Answer: PBP extends the glycan backbone during peptidoglycan synthesis.
50
Question: How is NAM (N-acetylmuramic acid) activated for incorporation into peptidoglycan?
Answer: NAM is activated by pyrophosphate before being incorporated into peptidoglycan by PBPs.
51
Question: What is released during the addition of NAM to the peptidoglycan chain by PBPs?
Answer: Undecaprenyl pyrophosphate is released during the addition of NAM to the peptidoglycan chain by PBPs.
52
Question: What is the primary activity of PBPs during peptidoglycan synthesis?
Answer: The primary activity of PBPs is their glycosyltransferase activity, which involves adding NAM-NAG (N-acetylglucosamine) disaccharide units to the growing peptidoglycan chain.
53
Question: How is undecaprenyl pyrophosphate recycled after its release during peptidoglycan synthesis?
Answer: Undecaprenyl pyrophosphate is dephosphorylated and then flipped to the cytoplasm for recycling.
54
Question: What is the effect of bacitracin on undecaprenyl pyrophosphate?
Answer: Bacitracin, an antibiotic, binds to undecaprenyl pyrophosphate and blocks its dephosphorylation.
55
Question: What is the consequence of bacitracin binding to undecaprenyl pyrophosphate?
Answer: Bacitracin binding prevents the recycling of undecaprenyl pyrophosphate, disrupting the synthesis of peptidoglycan.
56
Question: How does undecaprenyl pyrophosphate move between cellular compartments?
Answer: Undecaprenyl pyrophosphate is flipped between cellular compartments, from the cytoplasm to the membrane and back again, during its role in peptidoglycan synthesis.
57
Question: What is the significance of undecaprenyl pyrophosphate in peptidoglycan synthesis?
Answer: Undecaprenyl pyrophosphate serves as the carrier molecule for NAM and NAG units during the synthesis of peptidoglycan, crucial for bacterial cell wall formation.
58
Question: How can the peptidoglycan (PG) glycan backbone be degraded? (enzymes)
Answer: Bacterial enzymes are responsible for cell wall remodeling, while antimicrobial enzymes such as lysozyme can also degrade the PG glycan backbone.
59
Question: What is the function of lysozyme in the innate immune system?
Answer: Lysozyme is part of the innate immune system and is found in bodily secretions like saliva, tears, milk, and mucous. It cleaves the NAM-NAG bond in peptidoglycan, weakening the bacterial cell wall.
60
Question: Against which type of bacteria is lysozyme more effective?
Answer: Lysozyme is more effective against Gram-positive bacteria because their peptidoglycan layer is more exposed compared to Gram-negatives, which have an outer membrane.
61
Question: What is the consequence of lysozyme cleaving the NAM-NAG bond in peptidoglycan?
Answer: Cleavage of the NAM-NAG bond weakens the bacterial cell wall, making the bacterium more susceptible to other immune defenses or antimicrobial agents.
62
Question: What is the source of lysozyme in the human body?
Answer: Lysozyme is found in various bodily secretions, including saliva, tears, milk, and mucous.
63
Question: What is the structure (shape) of peptidoglycan strands?
Answer: Peptidoglycan strands are helical in shape.
64
Question: How are peptides arranged in relation to the glycan backbone of peptidoglycan?
Answer: Peptides extend outward from the glycan backbone of peptidoglycan.
65
Question: How does the helical structure of peptidoglycan contribute to bacterial cell wall function?
Answer: The helical structure provides strength and flexibility to the bacterial cell wall, allowing it to withstand osmotic pressure changes and mechanical stresses.
66
Question: What is the role of Penicillin-Binding Proteins (PBPs) in peptidoglycan structure?
Answer: PBPs cross-link peptides from different peptidoglycan strands, contributing to the overall stability of the bacterial cell wall.
67
Question: What is the significance of the cross-linking of peptides by PBPs in peptidoglycan structure?
Answer: Cross-linking of peptides by PBPs helps to form a strong and cohesive peptidoglycan network, essential for maintaining the structural integrity of the bacterial cell wall.
67
Question: What is attached to the NAM (N-acetylmuramic acid) sugar in peptidoglycan?
Answer: A pentapeptide is attached to the NAM sugar in peptidoglycan.
68
Question: Can the amino acid sequence of the pentapeptide vary?
Answer: Yes, the amino acid sequence of the pentapeptide can vary.
69
Question: What type of amino acids are present in the pentapeptide?
Answer: The pentapeptide contains D-amino acids, such as D-Ala.
70
Question: In what position is the diamino acid located within the pentapeptide?
Answer: The diamino acid is located in the third position of the pentapeptide.
71
Question: What are the two common diamino acids found in the third position of the pentapeptide?
Answer: The two common diamino acids found in the third position are L-lysine and meso-diaminopimelic acid (meso-Dap).
72
Question: How do Gram-negative bacteria cross-link their peptidoglycan strands?
Answer: Gram-negative bacteria cross-link between residue 3 (amino group of diamino acid) and residue 4 (carbonyl) of adjacent peptide chains.
73
Question: What type of bond is formed during the cross-linking process in Gram-negative bacteria?
Answer: An amide bond is formed between residue 3 and residue 4 during the cross-linking process in Gram-negative bacteria.
74
Question: What is released during the cross-linking process in Gram-negative bacteria?
Answer: Terminal D-alanine is released during the cross-linking process in Gram-negative bacteria.
75
Question: Why is cross-linking important in peptidoglycan structure?
Answer: Cross-linking between peptide chains strengthens the peptidoglycan layer, providing structural integrity to the bacterial cell wall.
76
Question: How does the cross-linking process differ between Gram-negative and Gram-positive bacteria?
Answer: In Gram-negative bacteria, cross-linking occurs between residue 3 and residue 4 of adjacent peptide chains, forming an amide bond and releasing terminal D-alanine, while in Gram-positive bacteria, cross-linking typically involves the formation of peptide bridges between adjacent peptide chains.
77
Question: How do Gram-positive bacteria cross-link their peptidoglycan strands?
Answer: Gram-positive bacteria cross-link their peptidoglycan strands through an interpeptide bridge between peptide chains.
78
Question: To which part of the peptide chain is the bridge attached in Gram-positive bacteria?
Answer: The bridge is attached to the diamino acid of the peptide chain in Gram-positive bacteria.
79
Question: What is released during the cross-linking process in Gram-positive bacteria?
Answer: Terminal D-alanine is released during the cross-linking process in Gram-positive bacteria.
79
Question: Does the composition of the interpeptide bridge vary among Gram-positive bacteria?
Answer: Yes, the composition of the interpeptide bridge can vary among Gram-positive bacteria. For example, in Staphylococcus aureus, it can consist of pentaglycine.
80
Question: Why is cross-linking important in peptidoglycan structure?
Answer: Cross-linking between peptide chains strengthens the peptidoglycan layer, providing structural integrity to the bacterial cell wall.
81
Question: How does the cross-linking process differ between Gram-negative and Gram-positive bacteria?
Answer: In Gram-positive bacteria, cross-linking involves the formation of an interpeptide bridge between peptide chains, while in Gram-negative bacteria, cross-linking occurs between specific residues of adjacent peptide chains, forming an amide bond.
82
Question: What enzyme domain is responsible for forming cross-links in peptidoglycan?
Answer: The transpeptidase domain of Penicillin-Binding Proteins (PBPs) is responsible for forming cross-links in peptidoglycan.
83
Question: What happens next in the transpeptidation process?
Answer: The diamino acid reacts with the complex formed by PBPs, resulting in the formation of an amide bond and cross-linking of peptidoglycan.
84
Question: Describe the initial step of transpeptidation by PBPs.
Answer: Initially, PBPs form a complex with the peptide chain.
85
Question: What is the target of β-lactam antibiotics in the transpeptidation mechanism?
Answer: The transpeptidase domain of PBPs is targeted by β-lactam antibiotics.
86
Question: How do β-lactam antibiotics affect the transpeptidation process?
Answer: β-lactam antibiotics inhibit the transpeptidase activity of PBPs by binding irreversibly to the active site, preventing the formation of cross-links in peptidoglycan and weakening the bacterial cell wall.
87
Question: What are examples of β-lactam antibiotics?
Answer: β-lactam antibiotics include penicillins, cephalosporins, and carbapenems.
88
Question: What is the chemical structure of β-lactam antibiotics?
Answer: β-lactam antibiotics contain a four-membered β-lactam ring in their chemical structure.
89
Question: What is significant about the discovery of penicillin G?
Answer: Penicillin G was the first β-lactam antibiotic in clinical use, initially produced by the Penicillium mold.
90
Question: When was the antibiotic activity of Penicillium observed?
Answer: The antibiotic properties of Penicillium were observed by Duchesne in 1896.
91
Question: What is the spectrum of activity of penicillin G?
Answer: Penicillin G has a narrow-spectrum of activity, primarily effective against Gram-positive bacteria.
91
Question: Who rediscovered the antibiotic properties of Penicillium and when?
Answer: The antibiotic properties of Penicillium were rediscovered by Alexander Fleming in 1928.
92
Question: Why are β-lactam antibiotics widely used?
Answer: β-lactam antibiotics are widely used due to their efficacy against a broad range of bacterial infections and relatively low toxicity to humans.
93
Question: How do β-lactam antibiotics inhibit the transpeptidase activity of PBPs?
Answer: β-lactam antibiotics inhibit the transpeptidase activity of PBPs by reacting with a serine residue in the active site of PBPs.
94
Question: How does weakening of the peptidoglycan by β-lactam antibiotics lead to cell lysis?
Answer: Weakening of the peptidoglycan by β-lactam antibiotics disrupts the structural integrity of the bacterial cell wall, leading to cell lysis and death.
95
Question: What is the consequence of β-lactam antibiotics reacting with serine in PBPs?
Answer: This reaction blocks PBPs from forming cross-links in peptidoglycan, weakening the cell wall structure.
96
Question: Are β-lactam antibiotics bactericidal or bacteriostatic?
Answer: β-lactam antibiotics are bactericidal, meaning they kill bacteria rather than merely inhibiting their growth.
97
Question: What is the primary mechanism of action of β-lactam antibiotics?
Answer: The primary mechanism of action of β-lactam antibiotics is the inhibition of peptidoglycan synthesis through blocking the transpeptidation reaction mediated by PBPs.
98
Question: What are β-lactamases?
Answer: β-lactamases are enzymes that degrade β-lactam antibiotics.
99
Question: What is the significance of β-lactamases in antibiotic resistance?
Answer: β-lactamases are a major antibiotic resistance mechanism, as they can degrade β-lactam antibiotics and render them ineffective.
100
Question: What type of reaction do serine β-lactamases (SBLs) catalyze?
Answer: Serine β-lactamases catalyze a reaction where serine reacts with the β-lactam ring of β-lactam antibiotics.
101
Question: How do serine β-lactamases (SBLs) hydrolyze β-lactam antibiotics?
Answer: Serine β-lactamases (SBLs) can hydrolyze the β-lactam ring of β-lactam antibiotics, similar to the mechanism of action of PBPs.
102
Question: What is the result of the hydrolysis of β-lactam antibiotics by β-lactamases?
Answer: The hydrolysis product of β-lactam antibiotics by β-lactamases is inactive, rendering the antibiotic ineffective against the bacteria producing the enzyme.
103
Question: What is the purpose of co-prescribing β-lactamase inhibitors with β-lactam antibiotics?
Answer: Co-prescribing β-lactamase inhibitors with β-lactam antibiotics helps to counteract the action of β-lactamase enzymes, thereby enhancing the effectiveness of the antibiotics.
104
Question: Can you provide an example of a combination antibiotic containing a β-lactamase inhibitor?
Answer: One example is Augmentin, which consists of amoxicillin and clavulanic acid.
105
Question: How do β-lactamase inhibitors work?
Answer: β-lactamase inhibitors work by stopping serine β-lactamases (SBLs) from degrading β-lactam antibiotics.
106
Question: What is the mechanism by which β-lactamase inhibitors block the action of SBLs?
Answer: Most β-lactamase inhibitors react with the serine residue in the active site of SBLs, thereby blocking the active site and preventing the enzyme from hydrolyzing β-lactam antibiotics.
107
Question: What is the result of combining a β-lactamase inhibitor with a β-lactam antibiotic?
Answer: Combining a β-lactamase inhibitor with a β-lactam antibiotic enhances the antibiotic's effectiveness by preventing bacterial resistance mediated by β-lactamase enzymes.
108
Question: What is MRSA?
Answer: MRSA stands for methicillin-resistant Staphylococcus aureus, which is a strain of Staphylococcus aureus bacteria that is resistant to methicillin and other β-lactam antibiotics.
109
Question: What is a major consequence of MRSA infections?
Answer: MRSA is a major cause of healthcare-associated infections, leading to increased morbidity and mortality rates in affected individuals.
110
Question: What gene encodes the resistance mechanism in MRSA?
Answer: The mecA gene encodes PBP2a, a β-lactam-resistant penicillin-binding protein.
111
Question: How does PBP2a confer resistance to β-lactam antibiotics?
Answer: PBP2a, being a β-lactam-resistant protein, has a shielded active site that only opens when bound to peptidoglycan, making it less susceptible to inhibition by β-lactam antibiotics.
112
Question: What is the significance of the shielded active site of PBP2a?
Answer: The shielded active site of PBP2a allows MRSA to continue cell wall synthesis even in the presence of β-lactam antibiotics, contributing to its resistance phenotype.
113
Question: What type of antibiotic is vancomycin?
Answer: Vancomycin is a glycopeptide antibiotic.
113
Question: Where is vancomycin produced?
Answer: Vancomycin is made by Streptomyces, which are soil bacteria known for producing various antibiotics.
114
Question: What types of infections is vancomycin typically used to treat? (Gram + or Gram -)
Answer: Vancomycin is primarily used for Gram-positive infections.
115
Question: What is the significance of vancomycin in the treatment of bacterial infections?
Answer: Vancomycin is often considered an antibiotic of last resort, reserved for severe infections that do not respond to other antibiotics due to its broad spectrum of activity and potency.
116
Question: How does vancomycin exert its antibacterial effect?
Answer: Vancomycin binds to the D-Ala-D-Ala dipeptide in the peptidoglycan peptide chain, thereby blocking the action of penicillin-binding proteins (PBPs) and inhibiting cell wall synthesis in susceptible bacteria.
117
Question: What are some examples of vancomycin-resistant microbes?
Answer: Vancomycin-resistant enterococci (VRE) are common examples of microbes that have developed resistance to vancomycin.
118
Question: How can changes to the peptidoglycan (PG) structure confer resistance to vancomycin?
Answer: Changes such as replacing D-Ala with D-lactate (D-Lac) or D-serine in the PG structure can confer resistance to vancomycin.
119
Question: What is the effect of replacing D-Ala with D-lactate or D-serine on vancomycin binding?
Answer: Such changes weaken vancomycin binding by approximately 1000-fold.
120
Question: Despite resistance to vancomycin, what can still occur in bacteria with altered PG structures?
Answer: Even in bacteria with altered PG structures that confer resistance to vancomycin, penicillin-binding proteins (PBPs) can still form cross-links in the cell wall.
121
Question: What is the significance of vancomycin resistance in clinical settings?
Answer: Vancomycin resistance poses a significant challenge in clinical settings, limiting treatment options for serious infections caused by resistant microbes such as VRE.
