The one-way transfer of genetic material from a donor cell to a recipient cell by direct cell to cell contact is:

Correct Answer: B

Rationale: The correct answer is B: Conjugation. Conjugation involves the transfer of genetic material from a donor cell to a recipient cell through direct cell-to-cell contact, typically mediated by a conjugative plasmid. During conjugation, a conjugative pilus forms a bridge between the donor and recipient cells, allowing the transfer of genetic material. A: Replication is the process of copying DNA to produce two identical DNA molecules. It does not involve the transfer of genetic material between cells. C: Transformation is the uptake and incorporation of foreign DNA from the environment by a bacterial cell. It does not require direct cell-to-cell contact. D: Transduction is the transfer of genetic material from one bacterium to another by a bacteriophage vector. It does not involve direct cell-to-cell contact between the donor and recipient cells.

Correct Answer: A

Rationale: Step 1: Treponema pallidum is a spirochete bacterium known to cause syphilis, a sexually transmitted infection. Step 2: Neisseria gonorrhoeae causes gonorrhea, not syphilis. Step 3: Chlamydia trachomatis is responsible for causing chlamydia, not syphilis. Step 4: Escherichia coli is commonly found in the gut and can cause gastrointestinal infections, not syphilis. Summary: Treponema pallidum is the correct answer as it is the specific bacterium associated with syphilis, while the other choices are responsible for different infections.

Correct Answer: A

Rationale: The correct answer is A: Corynebacterium diphtheriae. This bacterium causes diphtheria, characterized by a grayish pseudomembrane in the throat. The dark blue-staining rods with polar granules seen in microscopic examination are known as metachromatic granules, which are specific to Corynebacterium diphtheriae. Streptococcus pyogenes (choice B) causes strep throat but does not produce pseudomembranes. Haemophilus influenzae (choice C) can cause respiratory infections but does not typically present with a pseudomembrane. Neisseria gonorrhoeae (choice D) is a sexually transmitted bacterium and is not associated with the symptoms described.

Correct Answer: C

Rationale: The correct answer is C: To perform serodiagnostics of tuberculosis. Rationale: The negative reaction to the Mantoux test indicates absence of TB infection. Performing serodiagnostics will further confirm the absence of active infection. This is important to rule out TB before considering vaccination or isolation measures. Summary: A: BCG vaccination is not necessary as the boy shows a negative reaction to the Mantoux test. B: Repeating the test in a month is unnecessary as the initial test already showed a negative reaction. D: Isolating the boy is not warranted as there is no evidence of active TB infection.

Correct Answer: A

Rationale: The correct answer is A: Pseudomonas aeruginosa. This is because Pseudomonas is a Gram-negative rod, oxidase-positive, and a lactose non-fermenter. The presence of fever and chills suggests a systemic infection, which is common with Pseudomonas. Salmonella typhi, Shigella dysenteriae, and Escherimalia coli are all Gram-negative rods but are typically lactose fermenters and do not match the characteristics described in the question.

Correct Answer: A

Rationale: The correct answer is A: The pyocyanin released by Pseudomonas aeruginosa. Pyocyanin is a blue-green pigment produced by Pseudomonas aeruginosa, a common cause of nosocomial infections in burn patients. The presence of blue-green pus and gram-negative rods in the wound along with fever suggests an infection with Pseudomonas aeruginosa. The other choices are incorrect because E. Coli typically causes gastrointestinal infections and releases enterotoxins, Staphylococcus aureus releases hemolysins causing hemolysis of red blood cells, and Shigella dysenteriae releases shigatoxin causing bloody diarrhea, none of which match the clinical presentation described in the question.

Correct Answer: D

Rationale: The correct answer is D (All of the above). All three bacteria (Escherichia coli, Salmonella enterica, Pseudomonas aeruginosa) produce endotoxins that can lead to septic shock. Endotoxins are part of the outer membrane of Gram-negative bacteria and can trigger a strong immune response, leading to septic shock when released in large amounts. Escherichia coli and Salmonella enterica are common causes of bacterial septic shock, while Pseudomonas aeruginosa is known for its ability to produce endotoxins that contribute to severe infections and septic shock. Therefore, all three choices are correct in this context.

Correct Answer: A

Rationale: The correct answer is A: Metronidazole. It is the drug of choice for treating systemic amebiasis due to its high efficacy against Entamoeba histolytica. Metronidazole is well-absorbed, reaches therapeutic levels in the intestines, liver, and lungs, making it effective in treating the multi-organ involvement in this case. Choice B: Quiniofone is not a recommended treatment for amebiasis. Choice C: Tetracycline is not the first-line treatment for systemic amebiasis. Choice D: Quingamine is not a recognized drug for treating amebiasis.

Correct Answer: A

Rationale: The correct answer is A: Staphylococcus epidermidis. Step 1: Gram-positive cocci in clusters suggest staphylococci. Step 2: Catalase-positive and coagulase-negative narrows it down to Staphylococcus epidermidis, as it is catalase-positive and coagulase-negative. Staphylococcus aureus (B) is catalase-positive and coagulase-positive. Streptococcus pyogenes (C) is catalase-negative. Enterococcus faecalis (D) is catalase-negative and coagulase-negative.