Which of the following bacteria is responsible for causing botulism?

Correct Answer: A

Rationale: The correct answer is A, Clostridium botulinum. This bacterium produces botulinum toxin, leading to botulism. It is commonly found in soil and improperly canned food. Clostridium tetani causes tetanus, Staphylococcus aureus causes food poisoning, and Salmonella enterica causes salmonellosis. Therefore, A is correct due to its association with botulism, while the other choices are incorrect for causing different diseases.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Purple-stained diplococci suggest Gram-positive cocci. 2. Capsule presence is a characteristic of Streptococcus pneumoniae. 3. S. pneumoniae is known to form diplococci arrangements. 4. Therefore, the microorganism most likely present is Streptococcus pneumoniae. Summary: - B: Klebsiella pneumoniae is a Gram-negative rod, not a cocci. - C: Neisseria meningitidis is a Gram-negative diplococcus, not a capsule producer. - D: Escherichia coli is a Gram-negative rod, not a cocci or capsule producer.

Correct Answer: D

Rationale: The correct answer is D: Structure of cell wall. When studying a bacterial smear stained by the Ozheshko method, the focus is on the cell wall structure. This staining method highlights the cell wall morphology, allowing for detailed examination. Flagella, spores, and capsules are not typically visualized using this staining method. Flagella require special staining techniques, spores are usually observed through specific staining methods like Schaeffer-Fulton, and capsules are not easily visualized with the Ozheshko staining method. Therefore, the structure of the cell wall is the most relevant feature to study in this context.

Correct Answer: D

Rationale: The correct answer is D: Parenteral introduction of antitetanus serum. The symptoms described in the question, such as bilateral ptosis, mydriatic pupils, and difficulty reading, are indicative of tetanus infection. The source of infection could be the scratch on the knee, which allowed the tetanus bacteria to enter the body. The most appropriate therapy for tetanus is the administration of antitetanus serum to neutralize the tetanus toxin. Antibotulinic serum (choice A) is not appropriate as it is used for botulism, which presents differently. Disintoxication (choice B) is too general and does not address the specific cause of the symptoms. Antibiotics (choice C) are not effective in treating tetanus because it is caused by a toxin, not a bacterial infection. Therefore, the correct course of action is to administer antitetanus serum to the patient.

Correct Answer: D

Rationale: The correct answer is D, the rabies virus. Rabies virus has the widest infectious spectrum among the given choices because it can infect a wide range of mammals, including humans. This is due to its ability to infect nerve cells and spread throughout the central nervous system. The other choices have more limited infectious spectra. Anthrax bacillus primarily infects herbivores and humans, mumps virus infects mainly humans, and the causative agent of gonorrhea primarily infects humans through sexual contact. Therefore, the rabies virus is the correct answer as it has the broadest range of potential hosts.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Anopheles mosquitoes are the primary vectors for transmitting malaria. 2. They prefer stagnant water for breeding, common in tropical regions. 3. Culex mosquitoes primarily spread diseases like West Nile virus. 4. Aedes mosquitoes transmit diseases like Zika and dengue fever. 5. Mansonia mosquitoes are known for transmitting filarial diseases. Therefore, the correct answer is A (Anopheles), as they are specifically associated with spreading malaria.

Correct Answer: C

Rationale: The correct answer is C (25°C) because dimorphic fungi typically grow as molds at lower temperatures. At 25°C, the fungus is likely in its mold phase, which is the preferred temperature range for mold growth. Choices A, B, and D are incorrect because 15°C and 20°C are too low for optimal mold growth, and 37°C is too high as it typically favors the yeast phase of dimorphic fungi. Therefore, the preferred temperature for mold growth of a dimorphic fungus is 25°C.

Correct Answer: A

Rationale: The correct answer is A: Toxoplasmosis. Toxoplasmosis is a parasitic infection caused by Toxoplasma gondii, which can be transmitted to humans through contact with infected cat feces. During pregnancy, Toxoplasma infection can result in severe birth defects such as microcephaly and mental retardation in the child. In this case, the presence of a cat in the family and the child's abnormalities suggest a possible link to Toxoplasmosis. Other choices are incorrect because: B: Leishmaniasis is a parasitic disease transmitted by sandflies and does not typically cause the specific birth defects mentioned in the scenario. C: Dysentery is a bacterial infection that primarily affects the intestines and does not cause the neurological abnormalities described. D: Balantidiasis is a parasitic infection caused by Balantidium coli, a ciliated protozoan, but it is not associated with

Correct Answer: B

Rationale: The main function of bacterial pili is to facilitate conjugation and adhesion. Pili are hair-like appendages on bacteria that help in cell-to-cell interactions. They play a crucial role in bacterial conjugation by allowing the transfer of genetic material between cells. Additionally, pili help bacteria adhere to surfaces or host cells, aiding in colonization and biofilm formation. Choices A and D are incorrect because protein synthesis and toxin secretion are not the primary functions of pili. Choice C is incorrect as bacterial motility is mainly mediated by flagella, not pili.