A man died from an acute infectious disease accompanied by fever, jaundice, haemorrhagic rash on the skin and mucous membranes as well as by acute renal insufficiency. Histological examination of renal tissue (stained by Romanovsky-Giemsa method) revealed some convoluted bacteria looking like C and S letters. What bacteria were revealed?

Correct Answer: A

Rationale: The correct answer is A: Leptospira. The key features pointing to Leptospira are the presence of convoluted bacteria resembling C and S letters, which is characteristic of Leptospira species. Leptospirosis presents with fever, jaundice, haemorrhagic rash, and acute renal insufficiency. The other choices (B: Treponema, C: Spirilla, D: Borrelia) do not match the histological description or the clinical presentation of the case. Treponema is associated with syphilis, Spirilla with genus Spirochaeta, and Borrelia with Lyme disease, none of which match the given scenario.

Correct Answer: C

Rationale: The correct answer is C: gram-negative bacteria have an outer membrane that acts as an extra barrier. This outer membrane in gram-negative bacteria contains lipopolysaccharides and porins, which restrict the entry of antibiotics like penicillin. The outer membrane acts as an additional layer of protection, making it harder for penicillin to penetrate and reach its target, the peptidoglycan layer. Choices A, B, and D do not directly address the specific mechanism of resistance seen in gram-negative bacteria. Choice A focuses on transpeptidase enzyme quantity, which is not the primary reason for penicillin resistance. Choice B refers to β-lactamase enzymes in the periplasmic space, which are actually enzymes that degrade penicillin and contribute to resistance, but this is not unique to gram-negative bacteria. Choice D mentions a thicker cell wall, which is a characteristic of gram-positive bacteria, not gram-negative bacteria.

Correct Answer: C

Rationale: The correct answer is C: Louis Pasteur. He conducted experiments that definitively disproved the theory of spontaneous generation through his famous swan-neck flask experiment. By showing that microorganisms only appeared in the broth when exposed to air, Pasteur demonstrated that they did not arise spontaneously. John Needham's experiments were inconclusive, Joseph Lister is known for his contributions to antiseptic surgery, and Robert Koch is credited with developing Koch's postulates for identifying the causative agents of diseases, but neither of them directly contributed to ending the controversy about spontaneous generation.

Correct Answer: D

Rationale: The correct answer is D: Bacillus cereus. Bacillus intoxication is typically caused by Bacillus cereus, which is a common foodborne pathogen. This bacterium produces toxins that can lead to gastrointestinal illness when ingested. Bacillus subtilis (A) and Bacillus thuringiensis (B) are not known to cause intoxication in humans. Bacillus anthracis (C) causes anthrax, not intoxication. Therefore, Bacillus cereus is the correct choice for Bacillus intoxication.

Correct Answer: A

Rationale: The correct answer is A: Neisseria gonorrhoeae. This bacterium is a gram-negative diplococci commonly associated with gonorrhea, which presents with symptoms like painful urination. Neisseria gonorrhoeae is known to infect the urethra in males. Escherichia coli, Proteus vulgaris, and Klebsiella pneumoniae are all gram-negative bacteria, but they are not typically associated with urethral discharge or gonorrhea. E. coli is commonly associated with urinary tract infections, Proteus vulgaris with wound infections, and Klebsiella pneumoniae with pneumonia and other respiratory infections. Therefore, based on the patient's symptoms and the characteristics of the bacteria, Neisseria gonorrhoeae is the most appropriate causative agent in this case.

Correct Answer: A

Rationale: The correct answer is A: Bordetella pertussis. Whooping cough is caused by this bacteria, which specifically infects the respiratory tract. Bordetella pertussis produces toxins that lead to the characteristic symptoms of the disease. Haemophilus influenzae, Pseudomonas aeruginosa, and Streptococcus pneumoniae are not the causative agents of whooping cough. Haemophilus influenzae can cause respiratory infections, Pseudomonas aeruginosa is associated with hospital-acquired infections, and Streptococcus pneumoniae is a common cause of pneumonia and other respiratory infections, but none of these bacteria are responsible for whooping cough.

Correct Answer: C

Rationale: The correct answer is C: Papillomaviruses. Papillomaviruses are primarily transmitted through sexual contact, as they infect the skin and mucous membranes of the genital area. This transmission route is well-documented through research and epidemiological studies. Arenaviruses (A) are primarily transmitted through contact with infected rodents, not sexual contact. Togaviruses (B) are mainly transmitted by mosquitoes and ticks. Polyomaviruses (D) are typically spread through respiratory secretions or contaminated urine, not through sexual contact. Therefore, the most appropriate choice for viruses transmitted mainly through sexual contact is Papillomaviruses (C).

Correct Answer: C

Rationale: The Gram stain process involves staining bacterial cells with crystal violet and iodine, followed by decolorization and counterstaining. The primary differentiation is based on the cell wall structure, distinguishing bacteria into Gram-positive (retain purple color) and Gram-negative (lose purple color). This classification is crucial in microbiology for treatment decisions as it correlates with different antibiotic susceptibilities. Choices A, B, and D are incorrect because the Gram stain process does not primarily focus on flagella, shape, or motility of bacteria.

Correct Answer: B

Rationale: The correct answer is B: dermis. The papillary layer is located in the dermis, specifically at the junction with the epidermis. It contains capillaries, lymphatics, and sensory receptors, contributing to the skin's strength and elasticity. The epidermis (choice A) is the outermost layer of the skin, while the hypodermis (choice C) and subcutaneous layer (choice D) are deeper layers beneath the dermis, primarily composed of fat cells and connective tissue. Therefore, the papillary layer is part of the dermis, making choice B the correct answer.