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A patient with fever, headache, and neck stiffness had a cerebrospinal fluid sample showing Gram-negative diplococci. What is the most likely causative agent?
- A. Neisseria meningitidis
- B. Streptococcus pneumoniae
- C. Haemophilus influenzae
- D. Klebsiella pneumoniae
Correct Answer: A
Rationale: The correct answer is A: Neisseria meningitidis. This is because Neisseria meningitidis is a Gram-negative diplococcus known to cause bacterial meningitis, presenting with fever, headache, and neck stiffness. It is a common cause of meningitis in young adults and teenagers. Streptococcus pneumoniae (B) is a Gram-positive bacteria and a common cause of bacterial pneumonia, not meningitis. Haemophilus influenzae (C) is a Gram-negative coccobacillus that can cause meningitis, but it is less common in adults. Klebsiella pneumoniae (D) is a Gram-negative bacillus known to cause pneumonia and urinary tract infections, not meningitis.
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The oldest fossils of prokaryotes go back __________ billion years.
- A. 4.0 to 5.0
- B. 3.5 to 4.0
- C. 2.5 to 3.0
- D. 2.2 to 2.7
Correct Answer: B
Rationale: The correct answer is B: 3.5 to 4.0 billion years. This range aligns with the oldest known fossils of prokaryotes found in ancient rocks. Fossils dating back to this time period provide evidence of early life forms on Earth. Choices A, C, and D are incorrect because they fall outside the established timeline based on scientific evidence and fossil records. A (4.0 to 5.0 billion years) is too early for the oldest prokaryote fossils, as it predates the formation of Earth's atmosphere suitable for life. C (2.5 to 3.0 billion years) and D (2.2 to 2.7 billion years) are too recent for the oldest prokaryote fossils, as life is believed to have originated much earlier.
A 30-year-old patient complains about having abdominal pain and diarrhea for five days; body temperature rise up to 37, 5oC along with chills. The day before a patient had been in a forest and drunk from an open water reservoir. Laboratory analyses enabled to make the following diagnosis: amebic dysentery. What is the drug of choice for its treatment?
- A. Metronidazole
- B. Furazolidonum
- C. Levomycetin
- D. Phthalazol
Correct Answer: A
Rationale: The correct answer is A: Metronidazole.
Rationale:
1. Metronidazole is the drug of choice for amebic dysentery due to its effectiveness against the causative agent, Entamoeba histolytica.
2. Metronidazole has good tissue penetration and is able to reach the site of infection in the gut.
3. It is a bactericidal drug that acts by disrupting the DNA structure of the parasite.
4. Metronidazole is well-absorbed orally and has minimal side effects.
Summary of other choices:
B: Furazolidonum - Not the drug of choice for amebic dysentery. It is primarily used for treating bacterial diarrhea.
C: Levomycetin - Not effective against Entamoeba histolytica and not recommended for amebic dysentery.
D: Phthalazol - Not commonly used for amebic dysentery treatment. Metronidazole is preferred due
Almost half of all the STIs diagnosed in the United States are among:
- A. adolescents
- B. young adults
- C. young adults
- D. the elderly
Correct Answer: C
Rationale: The correct answer is C: young adults. Young adults are at a higher risk for sexually transmitted infections (STIs) due to factors such as engaging in risky sexual behaviors, lack of awareness, and inconsistent condom use. They are more likely to have multiple sexual partners and are less likely to seek regular STI screenings. Adolescents, while also at risk, may not make up almost half of all STI cases in the U.S. The elderly, on the other hand, are generally at a lower risk due to lower levels of sexual activity compared to young adults.
The virulence factors of bacteria include:
- A. size, adhesion, resistance, and mutation
- B. colonization, invasion, toxins, and adhesion
- C. toxins, evasion of body defenses, motility, and size
- D. colonization, chemotaxis, fermentation, and toxins
Correct Answer: B
Rationale: Rationale: The correct answer is B because virulence factors of bacteria are characteristics that enable them to cause disease. Colonization allows bacteria to establish and multiply in the host. Invasion refers to the ability to penetrate host tissues. Toxins are substances produced by bacteria that harm the host. Adhesion is crucial for bacteria to attach to host cells.
A: Size and mutation are not typical virulence factors. Resistance is not directly related to causing disease.
C: While toxins and evasion of body defenses are correct, motility and size are not universally considered virulence factors.
D: Chemotaxis and fermentation are not primary virulence factors, unlike colonization and toxins.
If skin-allergic samples for tuberculosis are negative:
- A. Antibiotics are prescribed
- B. Tuberculin is introduced
- C. A vaccine is administered
- D. None of the above
Correct Answer: B
Rationale: Step-by-step rationale for why choice B (Tuberculin is introduced) is correct:
1. Tuberculin test helps identify individuals with latent TB infection.
2. Negative skin-allergic samples suggest absence of active TB.
3. Introducing tuberculin can help confirm latent TB infection.
4. Antibiotics are not prescribed for negative skin-allergic samples.
5. Vaccines are not administered for TB diagnosis.
Summary:
- Choice A is incorrect as antibiotics are not prescribed for negative skin-allergic samples.
- Choice C is incorrect as vaccines are not used for TB diagnosis.
- Choice D is incorrect as introducing tuberculin is the appropriate step in this scenario.