Ch. 20 - Pathogenic Gram-Negative Cocci and Bacilli

Bauman - Microbiology with Diseases by Taxonomy 6th Edition

Bauman6th EditionMicrobiology with Diseases by TaxonomyISBN: 9780134832302Non è quello che usi tu?Cambia libro di testo

Bauman 6th Edition

Ch. 20 - Pathogenic Gram-Negative Cocci and Bacilli

Problema 1

Capitolo 20, Problema 1

The presence of lipid A in the outer membranes of Gram-negative bacteria.
a. Affects the formation of blood clots in the host
b. Causes these bacteria to be oxidase positive
c. Triggers the secretion of a protease enzyme to cleave IgA in mucus
d. Enables enteric bacteria to ferment glucose anaerobically

Guida verificata passo dopo passo

Step 1: Understand what lipid A is. Lipid A is a component of lipopolysaccharides (LPS) found in the outer membrane of Gram-negative bacteria. It acts as an endotoxin and plays a key role in the bacteria's interaction with the host immune system.

Step 2: Analyze each option in relation to lipid A's known biological effects. For example, lipid A is known to trigger immune responses, such as inflammation and fever, but does not directly affect blood clot formation.

Step 3: Consider option (a) - lipid A does not directly affect blood clot formation, so this is unlikely to be correct.

Step 4: Consider option (b) - oxidase positivity is related to the presence of cytochrome c oxidase enzyme, which is independent of lipid A, so this is unlikely.

Step 5: Consider options (c) and (d) - lipid A does not trigger secretion of IgA protease nor does it enable glucose fermentation anaerobically. Instead, lipid A's main role is as an endotoxin triggering immune responses.

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Lipid A and Endotoxin Activity

Lipid A is a component of lipopolysaccharides (LPS) in the outer membrane of Gram-negative bacteria. It acts as an endotoxin, triggering strong immune responses such as inflammation and fever when recognized by the host's immune system. This immune activation can lead to septic shock but does not directly affect blood clot formation.

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Lipids

Oxidase Test and Bacterial Identification

The oxidase test detects the presence of cytochrome c oxidase enzyme in bacteria. Being oxidase positive means the bacterium can use oxygen for respiration via this enzyme. However, the presence of lipid A in Gram-negative bacteria is unrelated to oxidase activity, which varies among species.

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The Ames Test

IgA Protease and Mucosal Immunity

IgA protease is an enzyme secreted by some bacteria to cleave IgA antibodies in mucus, helping them evade the host's immune defense on mucosal surfaces. This mechanism is independent of lipid A presence and is specific to certain pathogens, mainly Neisseria and Haemophilus species.

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Bacteria Avoid Antibodies by Producing IgA Proteases

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