A patient has a necrotizing phlegmon of his lower extremity. A doctor suspects a gas gangrene. Microscopy reveals grampositive bacilli. In order to confirm the diagnosis further bacteriological tests should include inoculation of the material into the following nutrient medium:

Correct Answer: A

Rationale: The correct answer is A: Kitt-Tarozzi medium. This medium is specifically designed to culture Clostridium species, the causative agents of gas gangrene. Clostridium species are gram-positive bacilli that produce gas during their metabolism. Inoculating the material into Kitt-Tarozzi medium allows for the selective growth of Clostridium species, aiding in the confirmation of a gas gangrene diagnosis. Other choices are incorrect: B: Endo agar is used for the isolation of gram-negative enteric bacteria. C: Meat-peptone agar is a general-purpose medium and not specific for Clostridium species. D: Levine agar is used for the isolation of Salmonella and Shigella species, not Clostridium.

Correct Answer: A

Rationale: The correct answer is A: cytomegalovirus. CMV is the most common virus transmitted during pregnancy, leading to potential serious complications for the fetus. It can cause birth defects, hearing loss, and developmental delays. CMV is commonly spread through bodily fluids. HIV (B) can also be transmitted during pregnancy but is less common. Herpes simplex virus (C) can be transmitted but typically results in localized infection. Epstein-Barr virus (D) is not commonly transmitted during pregnancy.

Correct Answer: C

Rationale: The correct answer is C: Transcription. Transcription is the process of synthesizing RNA from a DNA template. During transcription, RNA polymerase binds to the DNA and produces a complementary RNA strand. This process is essential for gene expression. Explanation for why other choices are incorrect: A: Transposition involves the movement of genetic elements within a genome, not the production of RNA from DNA. B: Translation is the process of synthesizing proteins from mRNA, not the production of RNA from DNA. D: RNA splicing is the process of removing introns and joining exons in pre-mRNA to produce mature mRNA, not the initial production of RNA from DNA.

Correct Answer: B

Rationale: The correct answer is B: Salmonella enterica. Typhoid fever is caused by the bacterium Salmonella enterica serotype Typhi. This specific strain of Salmonella is responsible for typhoid fever, a serious illness characterized by high fever, abdominal pain, and diarrhea. Escherichia coli (choice A) is not the causative agent of typhoid fever. Shigella flexneri (choice C) causes bacillary dysentery, not typhoid fever. Staphylococcus aureus (choice D) can cause food poisoning but is not associated with typhoid fever.

Correct Answer: A

Rationale: The correct answer is A: Tryptic soy agar is a general-purpose medium suitable for cultivating a wide range of microorganisms. It provides essential nutrients for growth without inhibiting specific types of bacteria. Blood agar (B), Mannitol salt agar (C), and MacConkey agar (D) are selective or differential media designed to promote the growth of specific types of bacteria or differentiate between different bacterial species. Therefore, they are not considered general-purpose mediums.

Correct Answer: A

Rationale: The correct answer is A: Mantoux test. The Mantoux test is used to screen for tuberculosis by injecting PPD intradermally. The presence of a delayed hypersensitivity reaction indicates prior exposure to Mycobacterium tuberculosis. The Schick test (B) is used to test for immunity to diphtheria, while the Dick test (C) is used to test for immunity to scarlet fever. Therefore, the correct use of PPD is in the Mantoux test for tuberculosis screening.

Correct Answer: D

Rationale: The correct answer is D because all the factors listed can contribute to the transmission of nosocomial infections. Medical dressings can harbor pathogens, breast milk can be a source of infection if not handled properly, and toys can serve as fomites for spreading germs. Choosing any other option would be incorrect as they all play a role in facilitating the transmission of nosocomial infections. It is important to consider all potential sources of infection in healthcare settings to effectively prevent the spread of nosocomial infections.

Correct Answer: D

Rationale: The correct answer is D, All of the above. Clostridium botulinum produces botulinum toxin causing botulism, Vibrio cholerae produces cholera toxin leading to severe diarrhea, and certain strains of Escherichia coli produce toxins causing gastrointestinal illness. Each bacterium has specific exotoxins that can result in severe gastrointestinal symptoms. Therefore, all three choices are correct in producing exotoxins that can cause severe gastrointestinal illness.

Correct Answer: B

Rationale: The correct answer is B because viruses can indeed be cultured on hen embryos, cell cultures, and experimental animals in vitro. This method allows for the replication and study of viruses outside the host organism. Option A is incorrect as viral cultivation is possible in laboratory settings. Option C is incorrect because while viruses can be grown on nutrient media, it is not the only method. Option D is incorrect as viruses can be cultured in various types of cell cultures, not just human embryonic ones.