microbiology chapter 14 test bank

Correct Answer: A

Rationale: The correct answer is A: Neisseria gonorrhoeae. This bacterium is a gram-negative diplococci commonly associated with gonorrhea, which presents with symptoms like painful urination. Neisseria gonorrhoeae is known to infect the urethra in males. Escherichia coli, Proteus vulgaris, and Klebsiella pneumoniae are all gram-negative bacteria, but they are not typically associated with urethral discharge or gonorrhea. E. coli is commonly associated with urinary tract infections, Proteus vulgaris with wound infections, and Klebsiella pneumoniae with pneumonia and other respiratory infections. Therefore, based on the patient's symptoms and the characteristics of the bacteria, Neisseria gonorrhoeae is the most appropriate causative agent in this case.

Correct Answer: C

Rationale: The correct answer is C: Streptococcus. Streptococcus pneumoniae is the most common etiological factor for community-acquired pneumonia in young adults. The symptoms described align with typical pneumococcal pneumonia presentation. Presence of pleural friction rub and infiltration in the X-ray support the diagnosis. The blood work showing elevated WBC count with a left shift (increased neutrophils and low lymphocytes) and elevated ESR is consistent with a bacterial infection. Legionella and Mycoplasma typically present with atypical pneumonia symptoms such as headache, confusion, and GI symptoms, which are not described in the case. Staphylococcus pneumonia is not a common cause of community-acquired pneumonia in young adults.

Correct Answer: D

Rationale: The thin microorganisms described with 12-14 equal ringlets and pale-pink sharp points are characteristic of Borrelia spirochetes, the causative agent of relapsing fever. The ringlet appearance corresponds to the characteristic coiled structure of Borrelia spirochetes. The length of 10-13 mkm falls within the typical size range of Borrelia spirochetes. This pathogen is commonly identified in Romanovsky-Giemsa stained samples from patients with relapsing fever. Summary of other choices: A: Leishmaniasis - Leishmania parasites are larger and do not have the described ringlets or pale-pink sharp points. B: Leptospirosis - Leptospira bacteria are not described as having ringlets or pale-pink sharp points. C: Surra - Surra is caused by Trypanosoma evansi, and the description does not match the characteristics of this parasite.

Correct Answer: A

Rationale: The correct answer is A: Clostridia. Fusiform spore-forming microorganisms that stain violet-blue with Gram's stain are characteristic of Clostridia. Clostridia are anaerobic, rod-shaped bacteria known for their ability to form spores and cause diseases such as tetanus and botulism. Summary of other choices: B: Streptococci are spherical, not fusiform, and typically do not form spores. C: Spirochaete are spiral-shaped bacteria and do not typically form spores. D: Actinomycete are filamentous bacteria that do not typically form spores and do not stain violet-blue with Gram's stain.

Correct Answer: C

Rationale: Step 1: Escherichia coli is known to produce a toxin called colibactin that targets cholesterol. Step 2: Colibactin disrupts cholesterol metabolism in host cells. Step 3: This disruption can lead to various health issues. Step 4: Streptococcus pyogenes produces different toxins, not specifically targeting cholesterol. Step 5: Corynebacterium diphtheriae produces diphtheria toxin, not targeting cholesterol. Step 6: Aeromonas hydrophila produces various toxins, but not known for targeting cholesterol. Summary: Escherichia coli produces toxins that specifically target cholesterol, making it the correct choice over the other options.