Ch. 20 - Pathogenic Gram-Negative Cocci and Bacilli

Bauman - Microbiology with Diseases by Taxonomy 6th Edition

Bauman6th EditionMicrobiology with Diseases by TaxonomyISBN: 9780134832302Not the one you use?Change textbook

Bauman 6th Edition

Ch. 20 - Pathogenic Gram-Negative Cocci and Bacilli

Problem 1

Chapter 20, Problem 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

Verified step by step guidance

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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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

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.

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.

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

Related Practice

Textbook Question

Match each bacterium with the disease or manifestations it causes.

1. _____ Escherichia coli

2. _____ Klebsiella pneumoniae

3. _____ Proteus mirabilis

4. _____ Salmonella enterica serotype Typhi

5. _____ Shigella flexneri

6. _____ Yersinia pestis

A. Bubonic plague

B. Typhoid fever

C. Gastroenteritis

D. Kidney stones

E. Pus-filled, bloody stools; cramps; fever; and diarrhea

F. Pneumonia

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Textbook Question

A physician prescribes fluid replacement to treat a patient with diarrhea. Although tests showed that a pathogenic enteric bacterium was the cause of the intestinal distress, an antimicrobial drug was not prescribed; why not?

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Textbook Question

Shown is a MacConkey agar plate. Describe the Gram reaction and lactose fermentation of the two different bacteria shown.

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Textbook Question

Label the following drawing using these words: adhesin, exotoxin, H antigens, hemolysin, iron-binding protein, K antigens, outer membrane (with common antigen, lipid A, and O antigen), fimbria, plasmid virulence genes, type III secretion system.

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