microbiology an introduction 13th edition test bank

Correct Answer: C

Rationale: Correct Answer: C - Immunological tolerance to the pathogen Rationale: 1. Immunological tolerance is when the immune system does not mount a response against specific antigens to prevent autoimmunity. 2. In the context of infection, tolerance to the pathogen means the immune system does not recognize the pathogen as a threat and does not initiate a protective response. 3. This lack of response leaves the host vulnerable to infection as there is no specific immune defense mechanism activated against the pathogen. Summary of incorrect choices: A: Opsonic action of antibody - enhances phagocytosis of pathogens B: Viral neutralization by specific antibody - prevents viral entry into host cells D: Neutralization of protein exotoxin - prevents the harmful effects of toxins produced by pathogens.

Correct Answer: C

Rationale: The correct answer is C because the main factor in the pathogenicity of diphtheria is the exotoxin produced by the bacterium Corynebacterium diphtheriae. This exotoxin inhibits protein synthesis in host cells, leading to tissue damage and the characteristic symptoms of diphtheria. A: The metachromatic bodies of Ernst-Babes are not the main factor in diphtheria pathogenicity. B: While endotoxins can contribute to the pathogenicity of some bacteria, in diphtheria, the main factor is the exotoxin. D: This is incorrect as the main factor in diphtheria pathogenicity is the exotoxin.

Correct Answer: B

Rationale: The correct answer is B because transformation in bacteria refers to the uptake of naked DNA from the environment. During transformation, bacteria take up free DNA from their surroundings and incorporate it into their own genome. This mechanism allows bacteria to acquire new genetic material and traits. Explanation for other choices: A: Transfer of DNA via phages refers to transduction, not transformation. C: Transfer of DNA via direct contact is known as conjugation, not transformation. D: Spore formation is a method of bacterial survival but is not related to transformation.

Correct Answer: A

Rationale: The correct answer is A: Escherichia coli. E. coli is the most common bacteria responsible for causing urinary tract infections due to its ability to adhere to the urinary tract lining and multiply rapidly. It is a normal inhabitant of the gut and can enter the urinary tract through improper hygiene practices. Salmonella enterica and Neisseria gonorrhoeae are typically associated with other infections like food poisoning and gonorrhea, respectively. Mycobacterium tuberculosis causes tuberculosis, not urinary tract infections. Thus, based on its prevalence and pathogenicity in the urinary tract, E. coli is the correct choice.

Correct Answer: A

Rationale: The correct answer is A: Escherichia coli. E. coli is a Gram-negative rod that typically has a greenish hue on MacConkey agar due to its ability to ferment lactose, producing acid that changes the pH indicator to green. E. coli is a common cause of diarrhea, particularly in cases of traveler's diarrhea. Salmonella (B), Shigella (C), and Klebsiella (D) are also Gram-negative rods but do not typically show a greenish hue on MacConkey agar and are less commonly associated with causing diarrhea compared to E. coli.