microbiology chapter 11 test bank

Correct Answer: A

Rationale: The correct answer is A: Staphylococcus epidermidis. This is supported by the characteristics of Gram-positive cocci in clusters, catalase-positive, and coagulase-negative. Staphylococcus epidermidis fits all these criteria, as it is a common skin commensal that can cause infections in immunocompromised individuals. Staphylococcus aureus (choice B) is catalase-positive and coagulase-positive. Streptococcus pyogenes (choice C) is catalase-negative. Enterococcus faecalis (choice D) is catalase-negative and not typically seen in clusters. Therefore, based on the given information, Staphylococcus epidermidis is the most likely causative agent.

Correct Answer: B

Rationale: The correct answer is B: Agglutination reaction. This test is commonly used to detect specific antibodies or antigens. In this case, it can be used to detect plague antigens in the rat tissues or antibodies in the villagers. This test is rapid, sensitive, and can help establish the presence of the causative agent quickly. A: Ring precipitation reaction is not typically used for diagnosing plague and is more commonly used in other types of infections. C: Passive agglutination reaction is not specific for plague and is more commonly used for detecting specific antibodies in diseases like syphilis. D: Neutralization reaction is not typically used for diagnosing plague and is more commonly used to determine the presence of neutralizing antibodies in viral infections.

Correct Answer: B

Rationale: Binary fission is a form of asexual reproduction where a single organism divides into two equal parts. Bacteria reproduce through binary fission, splitting into two identical daughter cells. Viruses are not considered living organisms and reproduce by infecting host cells. Fungi reproduce through spores or sexual reproduction. Helminths are parasitic worms that reproduce sexually. Therefore, the correct answer is B, bacteria, as they specifically utilize binary fission for reproduction.

Correct Answer: A

Rationale: The correct answer is A: Vibrio cholerae. This bacterium is the likely causative agent because it is known to cause severe diarrhea, and it is characterized by its motile, comma-shaped Gram-negative rods. Vibrio cholerae produces cholera toxin, leading to profuse watery diarrhea. Shigella dysenteriae causes dysentery with bloody diarrhea, Salmonella typhi causes typhoid fever, and Escherichia coli can cause various types of diarrhea but typically does not have a comma shape.

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. This bacterium is a common cause of pneumonia and is characterized by Gram-positive diplococci with a capsule. The presence of a capsule helps the bacterium evade the immune system and contributes to its virulence. Klebsiella pneumoniae (B) is a Gram-negative bacterium and does not typically have a capsule. Neisseria meningitidis (C) is a Gram-negative diplococcus and is associated with meningitis, not pneumonia. Staphylococcus aureus (D) is a Gram-positive bacterium, but it does not typically present as diplococci with a capsule in a sputum smear from a pneumonia patient.