Algae that contain agar in their cell walls belong to:

Correct Answer: B

Rationale: The correct answer is B: Rhodophyta. Rhodophyta is the phylum of red algae, which are known to contain agar in their cell walls. Agar is a gelatinous substance derived from these algae. Chrysophyta (A), Chlorophyta (C), and Phaeophyta (D) do not typically contain agar in their cell walls. Chrysophyta includes diatoms, Chlorophyta includes green algae, and Phaeophyta includes brown algae, none of which are known for agar production. Therefore, Rhodophyta is the correct choice based on the presence of agar in their cell walls.

Correct Answer: A

Rationale: The correct answer is A: Entamoeba histolytica. This protozoan causes amoebiasis, which presents with symptoms like diarrhea. The cysts with four nuclei found in the feces are characteristic of Entamoeba histolytica. This protozoan is known to cause invasive infection, leading to tissue destruction and ulcers in the intestines. Lamblia (choice B) typically presents with cysts containing two nuclei. Trichomonas (choice C) is a sexually transmitted parasite and does not form cysts. Balantidium (choice D) is a ciliated protozoan that does not have four nuclei in its cyst form.

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: Zielh-Neelsen stain. This stain is specifically used to detect acid-fast bacteria like Mycobacterium tuberculosis, the causative agent of renal tuberculosis. The staining process involves using carbol fuchsin to penetrate the mycolic acid layer of the bacterial cell wall, making it resistant to decolorization with acid-alcohol. This allows the red stained bacteria to be visualized under a microscope. Loeffler stain (B) is used for staining bacteria like diphtheria bacilli, Gram stain (C) is used for bacterial classification based on cell wall properties, and Aujeszky stain (D) is not a recognized staining method for detecting acid-fast bacteria.

Correct Answer: A

Rationale: The correct answer is A: Late congenital syphilis. The symptoms described align with late congenital syphilis, which includes saddle nose, high-arched palate, natiform skull, peg-shaped incisors, and notched cutting edge. Lymph nodes not being affected is also consistent with late congenital syphilis. Early congenital syphilis (B) typically presents with more severe symptoms at birth or shortly after. Tertiary syphilis (C) usually occurs years after initial infection and presents with different symptoms. Fluorosis (D) is caused by excessive fluoride intake and does not match the symptoms described.

Correct Answer: B

Rationale: The correct answer is B: Before antibiotic therapy is begun. Detecting penicillin-resistant, beta-lactamase-producing strains before antibiotic therapy is crucial to ensure proper treatment. If detected after therapy (choice A), it may lead to treatment failure. Detection during therapy (choice C) may result in delayed or ineffective treatment. Choice D is incorrect as early detection is essential for successful management.

Correct Answer: A

Rationale: The correct answer is A: Peritoneum. Normal flora refers to the microorganisms that naturally inhabit the human body without causing harm. The peritoneum is a sterile area, so it does not harbor normal flora. The urethra, vagina, and mouth all have normal flora due to their moist and warm environments, which provide an ideal habitat for microorganisms to thrive. The peritoneum, being a sterile cavity that houses organs like the stomach and intestines, does not have a natural microbial population like the other areas mentioned. Therefore, it does not contain normal flora.

Correct Answer: A

Rationale: The correct answer is A: evade host immune responses. Antigenic variation allows bacteria to change their surface antigens, making it difficult for the host immune system to recognize and attack them effectively. This enhances the bacteria's ability to evade immune responses and establish infection. B: Increase antibiotic susceptibility is incorrect because antigenic variation does not directly impact the susceptibility of bacteria to antibiotics. C: Increase peptidoglycan synthesis is incorrect because antigenic variation is not related to the synthesis of peptidoglycan, which is a major component of the bacterial cell wall. D: Enhance motility is incorrect because antigenic variation does not directly affect the motility of bacteria. In summary, antigenic variation in bacteria primarily serves to help them evade host immune responses, making option A the correct answer.

Correct Answer: A

Rationale: Step-by-step rationale for answer A: 1. Pseudomonas aeruginosa is known to cause burn wounds infections due to its ability to survive in moist environments. 2. It can cause severe pneumonia in patients with cystic fibrosis due to its resistance to antibiotics and ability to form biofilms. 3. It is a common cause of nosocomial infections in hospitals due to its ability to colonize medical equipment and surfaces. Summary of other choices: B. Pseudomonas aeruginosa typically does not cause food poisoning, as it is not a common pathogen associated with foodborne illnesses. C. Bacterial pharyngitis is usually caused by Streptococcus pyogenes, not Pseudomonas aeruginosa, making this choice incorrect. D. None of the above is incorrect as Pseudomonas aeruginosa is associated with specific infections mentioned in option A.