During an examination of feces from a patient with dysentery symptoms, large ciliated protozoa with a kidney-shaped macronucleus were found. What is the causative agent?

Correct Answer: A

Rationale: The correct answer is A: Balantidium coli. Balantidium coli is a large ciliated protozoa with a kidney-shaped macronucleus, commonly found in the feces of individuals with dysentery symptoms. Its morphology matches the description given in the question, making it the most likely causative agent. Summary of other choices: B: Entamoeba histolytica - This is not the correct answer because Entamoeba histolytica is a small amoeba with no cilia and a different nucleus shape. C: Giardia lamblia - This is not the correct answer as Giardia lamblia is a flagellated protozoa with a pear-shaped nucleus, different from the description provided. D: Trichomonas hominis - This is not the correct answer as Trichomonas hominis is a flagellated protozoa with multiple flagella and an undulating membrane, which does not match the characteristics of the

Correct Answer: A

Rationale: The Burri-Gins staining technique is used to identify capsule formation in bacteria. Capsules are protective layers around bacteria that can be visualized using this staining method. Capsules are important virulence factors for pathogens like Yersinia pestis, the causative agent of plague. This technique helps in differentiating encapsulated bacteria from non-encapsulated ones. Spore formation (B), acid resistance (C), and alkali resistance (D) are not properties that can be identified using the Burri-Gins technique, making them incorrect choices.

Correct Answer: D

Rationale: The correct answer is D: All of the above. HIV can be transmitted from mother to child during delivery through mixing of blood, during pregnancy through the placenta, and via breastmilk during lactation. Each mode of transmission carries a risk of HIV transmission to the child due to the presence of the virus in the mother's blood and bodily fluids. It is important to note that all three modes contribute to the risk of mother-to-child transmission of HIV, and preventive measures should be taken to reduce this risk. Option A, during delivery through mixing of blood, is correct as HIV can be transmitted through exposure to infected blood during childbirth. Option B, during pregnancy through placenta, is also correct as the virus can cross the placenta and infect the fetus. Option C, via breastmilk during lactation, is correct as HIV can be present in breastmilk and transmitted to the child through breastfeeding. Therefore, the preferred mode of transmission of HIV from a mother to a child

Correct Answer: B

Rationale: Gas gangrene is caused by Clostridium perfringens due to its ability to produce gas in tissues leading to necrosis. Other choices are incorrect: A (C. difficile causes diarrhea), C (C. tetani causes tetanus), and D (incorrect as B is the causative agent).

Correct Answer: A

Rationale: Rationale: 1. Endo agar inhibits the growth of Gram-positive bacteria. 2. Colorless colonies on Endo agar indicate lactose non-fermenting bacteria. 3. Shigella dysenteriae is a lactose non-fermenting, Gram-negative rod, causing dysentery. 4. Salmonella typhi, Escherichia coli, and Proteus vulgaris are lactose fermenters, so they would produce pink colonies on Endo agar. Therefore, the most likely causative agent is Shigella dysenteriae.

Correct Answer: C

Rationale: The correct answer is C: Thick peptidoglycan layer. Gram-positive bacteria have a thick peptidoglycan layer in their cell wall, which retains the crystal violet stain in the Gram staining process, leading to a purple color. This thick layer is a defining characteristic of Gram-positive bacteria. Rationale: A: Thin peptidoglycan layer is incorrect because Gram-positive bacteria have a thick peptidoglycan layer. B: Presence of an outer membrane is incorrect because Gram-positive bacteria lack an outer membrane. D: Presence of lipopolysaccharides is incorrect because lipopolysaccharides are typically found in the outer membrane of Gram-negative bacteria, not Gram-positive bacteria.

Correct Answer: C

Rationale: The correct answer is C: Clostridium perfringens. This bacterium is the causative agent of gas gangrene due to its ability to produce gas and toxins in anaerobic conditions. Clostridium tetani causes tetanus, Clostridium botulinum causes botulism, and Bacillus anthracis causes anthrax, not gas gangrene. Clostridium perfringens stands out as the correct choice based on its specific association with gas gangrene and its pathogenic mechanisms.

Correct Answer: D

Rationale: The correct answer is D: mixed infection. In a mixed infection, multiple infectious agents establish themselves at the same site, leading to a complex and diverse infection. This type of infection can involve different types of pathogens such as bacteria, viruses, fungi, and parasites. It can be challenging to diagnose and treat due to the presence of multiple pathogens. A: Chronic infection refers to an infection that persists over a long period but is typically caused by a single pathogen. B: Necrotizing infection is characterized by rapid tissue destruction but does not necessarily involve multiple infectious agents. C: Fatal infection does not specify the presence of multiple infectious agents, it simply implies that the infection leads to death. In summary, the correct answer, mixed infection, is the only choice that specifically describes the scenario of multiple infectious agents establishing themselves at the same site.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Mycobacterium tuberculosis is the causative agent of tuberculosis. 2. Mycobacterium tuberculosis is a slow-growing, acid-fast bacterium. 3. It primarily infects the lungs and can spread to other parts of the body. 4. Bacillus anthracis causes anthrax, Clostridium tetani causes tetanus, and Treponema pallidum causes syphilis. 5. Therefore, choice A, Mycobacterium tuberculosis, is the correct answer for the bacteria responsible for tuberculosis.