The primary mode of action of aminoglycosides is to:

Correct Answer: A

Rationale: Aminoglycosides primarily inhibit protein synthesis by binding to the 30S ribosomal subunit in bacteria. This action leads to misreading of mRNA and ultimately disrupts the translation process, resulting in faulty protein production and bacterial cell death. Incorrect choices: B: Aminoglycosides do not inhibit DNA replication. C: Aminoglycosides do not disrupt cell membrane integrity. D: Aminoglycosides do not inhibit folic acid synthesis. In summary, the correct choice (A) aligns with the known mechanism of action of aminoglycosides, making it the most appropriate answer.

Correct Answer: D

Rationale: The correct answer is D: P.aeruginosa. This bacterium is commonly found in water and soil, making its presence in indoor air an indicator of poor sanitation. Step 1: P.aeruginosa is an opportunistic pathogen known to cause infections in hospitals. Step 2: Its presence in the air indicates potential contamination and poor air quality. Step 3: Regular monitoring of P.aeruginosa levels can help assess the effectiveness of sanitation measures. Summary: A, B, and C are not suitable indicators of air sanitation in an enclosed space as they are not typically associated with environmental contamination or poor air quality.

Correct Answer: C

Rationale: The correct answer is C: Negative stain. Negative staining uses acidic dyes which are repelled by the bacterial cell wall components, highlighting bacteria with a large amount of peptidoglycan. Acid-fast stain (A) is used to identify Mycobacterium species with waxy cell walls. Gram stain (B) differentiates bacteria into Gram-positive and Gram-negative based on cell wall composition. Option D is a duplicate of option C and is incorrect.

Correct Answer: A

Rationale: Rationale: A is incorrect because whooping cough resurgence is mainly due to decreased vaccine immunity, not changing antigenicity. B is correct as P. aeruginosa can indeed cause infections with blue-green pus due to its pigment production. C is correct as H. influenzae type b capsule is a virulence factor contributing to invasive disease. D is correct as Legionella infection is acquired via inhalation of contaminated water aerosols. Therefore, A is incorrect as the rise in whooping cough is not due to changing antigenicity but vaccine immunity decline.

Correct Answer: B

Rationale: The correct answer is B: genotype. The genotype refers to the actual genetic makeup of an organism, including all the genes and alleles present in its DNA. This determines the traits and characteristics of an organism. Phenotype (A) is the observable physical or biochemical characteristics of an organism. Conjugation (C) is a process in bacteria involving the transfer of genetic material. Construct (D) is not a term related to genetics. Therefore, the correct choice is B as it specifically refers to the genetic composition of an organism.

Correct Answer: B

Rationale: Fimbriae in bacteria are hair-like appendages that help in adhesion to surfaces. This is essential for colonization and infection. Fimbriae do not provide motility (flagella do), facilitate protein synthesis (ribosomes do), or help in endospore formation (specialized structures do). Adhesion is the primary function of fimbriae, allowing bacteria to stick to host cells or abiotic surfaces.

Correct Answer: A

Rationale: The correct answer is A: Bacteria. Urinary tract infections (UTIs) are primarily caused by the invasion of bacteria into the urinary tract. Bacteria, especially Escherichia coli (E. coli), are the most common culprits. They enter the urinary tract through the urethra and can multiply in the bladder, leading to infection. Viruses (choice B) and fungi (choice C) are not typical causes of UTIs. "None of the above" (choice D) is incorrect as bacteria are indeed the main cause of UTIs.

Correct Answer: A

Rationale: The correct answer is A: Peroxidase and catalase. Peroxidase and catalase are enzymes that break down hydrogen peroxide into water and oxygen. Peroxidase helps in breaking down low levels of hydrogen peroxide, while catalase is crucial for breaking down high levels of hydrogen peroxide efficiently. This process is important for organisms to prevent damage from reactive oxygen species. Choices B, C, and D are incorrect: B: Oxygenase and hydroxylase are enzymes involved in different biochemical reactions and do not break down hydrogen peroxide. C: Cytochrome oxidase and cytochrome B5 are involved in electron transport chain reactions and not in breaking down hydrogen peroxide. D: Oxygenase and catalase are not correct as oxygenase is not involved in hydrogen peroxide breakdown, only catalase is.

Correct Answer: A

Rationale: The correct answer is A: Isoniazid. Isoniazid is a first-line drug for treating active pulmonary tuberculosis due to its high efficacy and low toxicity. It works by inhibiting the synthesis of mycolic acids in the bacterial cell wall. Sulfalen, Cyclocerine, and Ethionamide are not first-line drugs for tuberculosis. Sulfalen is used for urinary tract infections, Cyclocerine for drug-resistant tuberculosis, and Ethionamide as a second-line drug for multidrug-resistant tuberculosis. Therefore, Isoniazid is the most appropriate initial choice for treating active focal pulmonary tuberculosis.