Which of the following bacteria are capable of surviving in high-salinity environments?

Correct Answer: A

Rationale: The correct answer is A: Halophiles. Halophiles are bacteria that thrive in high-salinity environments due to their ability to tolerate high salt concentrations. They have adapted mechanisms to maintain osmotic balance and survive in such extreme conditions. Thermophiles (B) thrive in high-temperature environments, not high-salinity. Acidophiles (C) prefer acidic conditions, not high-salinity. Mesophiles (D) grow optimally at moderate temperatures and are not specifically adapted to high-salinity environments.

Correct Answer: A

Rationale: The correct answer is A: Tuberculine. The Mantoux test involves injecting tuberculin, a protein derivative of Mycobacterium tuberculosis, under the skin. This test helps determine if a person has been exposed to the bacteria that cause TB. Administering tuberculin is crucial for the Mantoux test as it triggers a delayed-type hypersensitivity reaction in individuals previously exposed to TB. Choice B (BCG vaccine) is incorrect because BCG does not interfere with the Mantoux test results. Choice C (DPT vaccine) is incorrect as it is used for immunization against diphtheria, pertussis, and tetanus, not for diagnosing TB. Choice D (Tularin test) is incorrect as it is not a recognized immunobiological agent for TB diagnosis.

Correct Answer: B

Rationale: The correct answer is B: Zoonosis. Tularemia is primarily a zoonotic disease, meaning it is transmitted from animals to humans. The bacterium that causes tularemia, Francisella tularensis, commonly infects animals like rabbits, rodents, and ticks, which serve as reservoir hosts. Humans can get infected through direct contact with infected animals, insect bites, or contaminated water or soil. This zoonotic nature of tularemia distinguishes it from anthroponosis (A), which is transmitted only between humans, and sapronosis (C), which is transmitted through non-living environmental sources. Choice D is incorrect because there is a correct answer, which is zoonosis.

Correct Answer: C

Rationale: The correct answer is C: Van Leeuwenhoek. Van Leeuwenhoek was a Dutch scientist known for his pioneering work in microscopy. He was the first to observe microbial life, including bacteria on teeth, using his handmade microscopes in the 17th century. Jenner (choice A) is known for developing the smallpox vaccine, not for microbial observations. Semmelweis (choice B) discovered the importance of handwashing in preventing infections. Pasteur (choice D) is famous for his work on pasteurization and germ theory, but not specifically for observing microbial life on teeth. Van Leeuwenhoek's meticulous observations and groundbreaking discoveries make him the correct choice in this context.

Correct Answer: A

Rationale: Rationale: Vibrio cholerae produces the exotoxin responsible for severe diarrhea. It causes cholera by disrupting the normal functioning of the intestines. Clostridium botulinum causes botulism, not diarrhea. Streptococcus pyogenes causes strep throat and skin infections. Salmonella enterica causes food poisoning, not severe diarrhea. Therefore, the correct answer is A.

Correct Answer: C

Rationale: The correct answer is C: nucleotides. Nucleotides are the structural units of nucleic acids, consisting of a nitrogenous base, a sugar molecule, and a phosphate group. The nitrogenous base can be adenine, thymine, cytosine, guanine, or uracil. Histones (B) are proteins that DNA wraps around in chromosomes, not structural units of nucleic acids. Nucleosides (A) are composed of a nitrogenous base and a sugar molecule but lack the phosphate group present in nucleotides. N-bases (D) is not a recognized term in biology and does not accurately describe the structural units of nucleic acids.

Correct Answer: A

Rationale: The correct answer is A: tRNA. Anticodons are sequences of nucleotides found on tRNA molecules that complement the codons on mRNA during translation. tRNA molecules carry specific amino acids to the ribosome based on the codon-anticodon pairing. Option B, rRNA, forms the structure of the ribosome and is not directly involved in anticodon recognition. Option C, mRNA, contains codons but not anticodons. Option D, ribosomes, are the site of protein synthesis but do not contain the anticodons themselves.

Correct Answer: A

Rationale: Rationale: 1. Gram-positive cocci in clusters point to Staphylococcus or Micrococcus. 2. Catalase-positive eliminates Streptococcus. 3. Coagulase-positive distinguishes Staphylococcus aureus. 4. Thus, the causative agent is Staphylococcus aureus. Summary: - B: Streptococcus pyogenes is catalase-negative. - C: Enterococcus faecalis is catalase-negative. - D: Micrococcus luteus is catalase-positive but coagulase-negative.

Correct Answer: C

Rationale: The correct answer is C: Ebola virus. The patient's symptoms align with Ebola virus infection, including fever, severe hemorrhagic syndrome, and CNS involvement. Ebola virus is known to cause hemorrhagic fevers with high mortality rates. A: SARS CoV causes Severe Acute Respiratory Syndrome, which typically presents with respiratory symptoms, not hemorrhagic fever. B: Lymphocytic choriomeningitis virus usually causes a mild illness with flu-like symptoms, not severe hemorrhagic syndrome. D: ECHO 9 virus is associated with aseptic meningitis, not hemorrhagic fever.