The normal flora present in the healthy male reproductive system is best characterized as:

Correct Answer: C

Rationale: Rationale: 1. The male reproductive system is considered sterile as it does not have a natural microbiota. 2. Any presence of microorganisms in this system could indicate an infection or disease. 3. Therefore, choice C, sterile with no normal flora, is the best characterization. Summary: A: Incorrect - The male reproductive system does not typically have gram-positive rods. B: Incorrect - Acid-fast rods are not part of the normal flora in the male reproductive system. D: Incorrect - The male reproductive system does not typically have gram-positive spore formers.

Correct Answer: A

Rationale: The correct answer is A: Clostridium botulinum. This bacterium produces the neurotoxin responsible for botulism. Clostridium perfringens causes gas gangrene, not botulism. Escherichia coli and Salmonella enterica are not associated with botulism. Clostridium botulinum is the only bacterium known to produce the toxin causing botulism.

Correct Answer: C

Rationale: The correct answer is C: Carry genes for antibiotic resistance. Bacterial plasmids are small, circular DNA molecules that can be transferred between bacteria, carrying genes such as antibiotic resistance. This allows bacteria to survive in the presence of antibiotics. Plasmids do not directly play a role in protein synthesis (choice A) or DNA replication (choice B). Plasmids are not responsible for motility (choice D) as that function is usually carried out by flagella or other cellular structures.

Correct Answer: C

Rationale: The correct answer is C because the main factor in the pathogenicity of diphtheria is the exotoxin produced by the bacterium Corynebacterium diphtheriae. This exotoxin inhibits protein synthesis in host cells, leading to tissue damage and the characteristic symptoms of diphtheria. A: The metachromatic bodies of Ernst-Babes are not the main factor in diphtheria pathogenicity. B: While endotoxins can contribute to the pathogenicity of some bacteria, in diphtheria, the main factor is the exotoxin. D: This is incorrect as the main factor in diphtheria pathogenicity is the exotoxin.

Correct Answer: B

Rationale: The correct answer is B: As a result of mosquito's bites. Sleeping sickness, also known as African trypanosomiasis, is caused by the parasite Trypanosoma transmitted by tsetse flies, not mosquitoes. Tsetse flies are primarily found in Africa, not South America. Choice A is incorrect as bug bites do not transmit sleeping sickness. Choice C is incorrect as contaminated fruits and vegetables do not transmit the disease. Choice D is incorrect as dirty hands do not play a role in the transmission of sleeping sickness.

Correct Answer: C

Rationale: The correct answer is C: Escherichia coli. E.coli is the most common urinary tract pathogen due to its ability to adhere to and infect the urinary tract epithelium. It accounts for approximately 80-85% of urinary tract infections. It possesses specific virulence factors that enable it to colonize and cause infection in the urinary tract. Proteus mirabilis (A) is known for causing complicated UTIs, but it is less common than E.coli. Staphylococcus aureus (B) is not a common urinary pathogen. Pseudomonas aeruginosa (D) is more commonly associated with hospital-acquired infections, rather than community-acquired urinary tract infections.

Correct Answer: A

Rationale: The correct answer is A: TRUE. Poxviruses are indeed the largest viruses known, ranging from 200-450 nm in size, which is close to the resolution limit of a light microscope. This makes them almost visible under a light microscope. Explanation: 1. Poxviruses have complex structures and are among the largest viruses. 2. Light microscopes have a resolution limit of around 200 nm. 3. Poxviruses fall within the size range that is close to the resolution limit of a light microscope. 4. Therefore, poxviruses are almost visible under a light microscope. Summary: Choice B is incorrect because poxviruses are indeed large enough to be almost visible under a light microscope. Choice C is incorrect as it implies uncertainty, but poxviruses are consistently close to the resolution limit of a light microscope. Choice D is incorrect as the size of poxviruses being almost visible under a light microscope is a factual statement, not dependent

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: Step 1: Understand haematogenic spread means bacteria traveling through blood. Step 2: Urinary tract infections typically occur due to bacteria entering through urethra, not via blood. Step 3: Choice A states bacterial UTIs are usually after haematogenic spread, which is incorrect. Step 4: Therefore, Choice A is NOT true for UTIs. Summary: B, C, and D are incorrect as they align with typical characteristics of UTIs.