Lecture 10 Flashcards
Question: How is bacterial susceptibility to an antibiotic measured?
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.
Question: What is the difference between E. coli and S. aureus in terms of Gram staining?
Answer: E. coli is Gram-negative, while S. aureus is Gram-positive.
Question: What impact does cell wall structure have on antibiotic susceptibility?
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.
Question: Which type of bacteria generally have a thicker peptidoglycan layer in their cell wall?
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.
Question: How might differences in cell wall structure influence MIC values between Gram-negative and Gram-positive bacteria?
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.
Question: What additional structure do Gram-negative bacteria have outside of the peptidoglycan layer?
Answer: Gram-negative bacteria have an outer membrane outside of the peptidoglycan layer.
Question: What is the function of the outer membrane in Gram-negative bacteria?
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.
Question: What is the composition of the outer membrane in Gram-negative bacteria?
Answer: The outer membrane of Gram-negative bacteria is composed of a lipid bilayer.
Question: How does the presence of an outer membrane affect the susceptibility of Gram-negative bacteria to antibiotics?
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.
Question: What is the composition of the outer leaflet of the Gram-negative outer membrane?
Answer: The outer leaflet of the Gram-negative outer membrane is composed of lipopolysaccharides (LPS).
Question: What is the composition of the inner leaflet of the Gram-negative outer membrane?
Answer: The inner leaflet of the Gram-negative outer membrane is composed of phospholipids.
Question: Which type of bacteria contain lipopolysaccharides (LPS) in their outer membrane?
Answer: Lipopolysaccharides (LPS) are exclusively found in the outer membrane of Gram-negative bacteria.
Question: What is the function of the outer membrane in Gram-negative bacteria?
Answer: The outer membrane serves as an impermeable barrier, excluding antibiotics, host defenses, and other molecules from entering the bacterial cell.
Question: Why are membrane proteins important in the Gram-negative outer membrane?
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.
Question: What are the chemical properties of lipopolysaccharide (LPS) that contribute to its barrier function?
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.
Question: What are the three main parts of lipopolysaccharide (LPS)?
Answer: Lipopolysaccharide (LPS) consists of three main parts: Lipid A, core polysaccharides, and O-antigen.
Question: What is the function of Lipid A in lipopolysaccharide (LPS)?
Answer: Lipid A anchors the LPS molecule to the outer membrane of Gram-negative bacteria and is responsible for its endotoxic properties.
Question: What is the function of O-antigen in lipopolysaccharide (LPS)?
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.
Question: What role do core polysaccharides play in lipopolysaccharide (LPS)?
Answer: Core polysaccharides provide structural stability to the LPS molecule and help to connect Lipid A to the O-antigen.
Question: How is Lipid A positioned in the Gram-negative outer membrane?
Answer: Lipid A is embedded in the outer membrane of Gram-negative bacteria, anchoring the lipopolysaccharide (LPS) molecule to the membrane.
Question: What is the chemical composition of Lipid A?
Answer: Lipid A consists of glucosamine sugars attached to fatty acids, typically containing phosphorylated groups which contribute to its negatively charged nature.
Question: What is the role of Lipid A in the toxicity of LPS?
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.
Question: What happens when cells containing Lipid A are lysed?
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.
Question: What are some of the consequences of Lipid A-induced toxicity?
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.