Microbiology An Introduction 12th Edition Test Bank

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Microscopical examination of an infiltrate removed from the submandibular skin area of a 30 y.o. man revealed foci of purulent fluxing surrounded by maturing granulations and mature connective tissue, the pus contains druses consisting of multiple short rod-like elements with one end attached to the homogenous centre. What disease is it?

  • A. Actinomycosis
  • B. Tuberculosis
  • C. Syphilis
  • D. Candidosis
Correct Answer: A

Rationale: The correct answer is A: Actinomycosis. This is supported by the presence of purulent foci with druses consisting of short rod-like elements attached to a homogenous center, which is characteristic of Actinomyces species. Actinomycosis commonly presents with granulation tissue and connective tissue formation.

B: Tuberculosis does not typically present with druses containing short rod-like elements.
C: Syphilis does not typically present with purulent foci or druses.
D: Candidosis does not typically present with the described features of purulent fluxing and druses with short rod-like elements.

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Bacteriophages reproduce by:

  • A. Division
  • B. Mitosis
  • C. Meiosis
  • D. None of them
Correct Answer: D

Rationale: Bacteriophages are viruses that infect bacteria, not living organisms. They do not reproduce through division, mitosis, or meiosis because they lack the cellular machinery for these processes. Instead, bacteriophages replicate by inserting their genetic material into a host bacterium and hijacking its cellular machinery to produce new viral particles. Therefore, the correct answer is D - None of them. Division and mitosis involve cellular division in living organisms, while meiosis is a specialized process for sexual reproduction in eukaryotic organisms, none of which apply to bacteriophages.

Which of the following is likely to be the most frequently used portal of entry for pathogens?

  • A. Skin
  • B. Gastrointestinal tract
  • C. Respiratory tract
  • D. Conjunctiva
Correct Answer: C

Rationale: The correct answer is C: Respiratory tract. The respiratory tract is likely the most frequently used portal of entry for pathogens because it is constantly exposed to the external environment and has a large surface area lined with mucous membranes that can trap and facilitate the entry of pathogens. Additionally, the respiratory tract serves as a direct pathway for pathogens to reach the bloodstream and other organs. Skin (choice A) is a physical barrier that can prevent pathogen entry, while the gastrointestinal tract (choice B) has acidic pH and enzymes that can kill many pathogens. Conjunctiva (choice D) is a less common portal of entry compared to the respiratory tract due to its smaller surface area and protective mechanisms such as tears.

The neonatal infection referred to as “sticky eye†is caused by:

  • A. Streptococcus
  • B. herpes simplex
  • C. Staphylococcus
  • D. Escherichia
Correct Answer: C

Rationale: The correct answer is C: Staphylococcus. Staphylococcus is a common bacteria that can cause neonatal conjunctivitis, also known as "sticky eye." Staphylococcal conjunctivitis presents with symptoms like eye redness, discharge, and swelling. Streptococcus (choice A) typically causes throat infections, herpes simplex (choice B) causes genital or oral sores, and Escherichia (choice D) is a bacteria commonly found in the gastrointestinal tract and is not typically associated with neonatal conjunctivitis. Therefore, the most likely pathogen causing "sticky eye" in newborns is Staphylococcus.

A patient with a productive cough and fever had a Gram-positive cocci isolated from a sputum sample. The bacteria were catalase-positive and coagulase-negative. What is the likely microorganism?

  • A. Staphylococcus epidermidis
  • B. Staphylococcus aureus
  • C. Streptococcus pneumoniae
  • D. Neisseria meningitidis
Correct Answer: A

Rationale: The correct answer is A: Staphylococcus epidermidis.
1. Gram-positive cocci suggest a staphylococcal species.
2. Catalase-positive indicates it belongs to the Staphylococcus genus.
3. Coagulase-negative rules out Staphylococcus aureus.
4. Staphylococcus epidermidis is a common cause of infections in immunocompromised patients.
Summary:
- B: Staphylococcus aureus is coagulase-positive.
- C: Streptococcus pneumoniae is a Gram-positive diplococci.
- D: Neisseria meningitidis is a Gram-negative diplococci.

Which bacteria are capable of producing exotoxins?

  • A. Clostridium tetani
  • B. Staphylococcus aureus
  • C. Escherichia coli
  • D. All of the above
Correct Answer: D

Rationale: The correct answer is D: All of the above. Clostridium tetani, Staphylococcus aureus, and Escherichia coli are all capable of producing exotoxins. Exotoxins are proteins released by bacteria that can cause damage to the host. Clostridium tetani produces tetanospasmin, causing tetanus. Staphylococcus aureus produces toxins like enterotoxin and toxic shock syndrome toxin-1. Escherichia coli can produce Shiga toxin and heat-labile toxin. Therefore, all three bacteria listed can produce exotoxins, making choice D the correct answer. Choices A, B, and C are incorrect as they do not encompass all the bacteria capable of producing exotoxins.

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