A wound swab from a patient with severe tissue infection revealed Gram-positive rods in chains producing gas. The bacteria were spore-forming. What is the causative agent?

Correct Answer: A

Rationale: The correct answer is A: Clostridium perfringens. This bacterium is a Gram-positive rod that forms chains and produces gas due to its ability to ferment carbohydrates. It is also spore-forming, which helps it survive harsh conditions. Clostridium perfringens is commonly associated with severe tissue infections and gas gangrene. Choice B: Bacillus anthracis is also a spore-forming Gram-positive rod but is not typically associated with gas production or severe tissue infections. Choice C: Clostridium tetani is a spore-forming bacterium that causes tetanus, not severe tissue infections with gas production. Choice D: Pseudomonas aeruginosa is a Gram-negative bacterium and does not fit the description provided in the question.

Correct Answer: D

Rationale: The correct answer is D: Terminally. In Clostridium tetani, spores are located at the terminal end of the cell. This positioning helps the spores to be released easily when the cell lyses, aiding in the spread of the bacteria. Paracentrally (A) and centrally (C) would not be as efficient for spore release. Subterminally (B) is also incorrect as the spores are specifically located at the terminal end of the cell, not just near it.

Correct Answer: B

Rationale: The correct answer is B because live vaccines can potentially revert to a virulent form, although this is extremely rare. This is due to the live attenuated virus in the vaccine potentially mutating back to a more dangerous form. Live vaccines are designed to be weakened but there is a small risk of reversion. Therefore, statement B is not correct. A: This statement is correct as immunocompromised individuals may have adverse reactions to live vaccines due to their weakened immune system. C: This statement is correct as microbes with many serotypes can make it challenging to develop a vaccine that covers all variations. D: This statement is correct as side effects to vaccination, although usually mild and temporary, can occur in some individuals.

Correct Answer: B

Rationale: The correct answer is B: septicemia. Septicemia specifically refers to the presence of bacteria in the bloodstream, leading to a systemic inflammatory response. Bacteremia (choice A) is simply the presence of bacteria in the blood without the systemic inflammatory response. Shock (choice C) is a state of circulatory collapse, often seen in severe septicemia. Bloodborne infection (choice D) is a general term for infections transmitted through the blood but does not specifically refer to the condition of bacterial multiplication causing toxicity.

Correct Answer: A

Rationale: The correct answer is A: Spores. The Ozheshko method is used to stain spores, which are resistant structures produced by certain bacterial species. By studying the smear of streptobacillus preparation under oil immersion, one can observe the presence of spores as distinct, oval bodies within the bacteria. Spores are important for bacterial survival in harsh conditions. Summary: B: Capsules are not typically stained using the Ozheshko method. Capsules are usually visualized using negative staining techniques. C: Flagella are not stained by the Ozheshko method. Flagella are visualized using special staining techniques like the flagella stain. D: Inclusions are not specifically stained by the Ozheshko method. Inclusions are often observed using techniques that highlight cellular structures or components.

Correct Answer: A

Rationale: The correct answer is A: Giardia lamblia. Giardia lamblia is a protozoan parasite that causes foul-smelling diarrhea. The trophozoites of Giardia lamblia have two nuclei and flagella, which are characteristic features seen on stool microscopy. The presence of these specific features helps differentiate Giardia lamblia from the other options. Entamoeba histolytica (B) typically presents with one nucleus and lacks flagella. Trichomonas vaginalis (C) is a sexually transmitted parasite with a different morphology. Balantidium coli (D) is a ciliated parasite, not flagellated like Giardia lamblia.

Correct Answer: B

Rationale: The correct answer is B: Gram-negative bacteria. Gram-negative bacteria have an outer membrane containing lipopolysaccharides (LPS). In the Gram staining technique, these bacteria appear pink/red due to the thin peptidoglycan layer, which allows the crystal violet stain to be washed out, revealing the safranin counterstain. Gram-positive bacteria (choice A) have a thick peptidoglycan layer but lack an outer membrane with LPS. Choice C is incorrect since only Gram-negative bacteria possess LPS in their outer membrane. Choice D is incorrect as all bacteria can be classified as either Gram-positive or Gram-negative based on their cell wall structure.

Correct Answer: A

Rationale: The correct answer is A: Shigella dysenteriae. This bacterium produces Shiga toxin, which inhibits protein synthesis by inactivating the ribosomes. Shigella dysenteriae is known to cause severe gastrointestinal infections. Choice B: Escherichia coli typically does not produce toxins that inhibit protein synthesis. E. coli strains may produce toxins that cause diarrhea. Choice C: Clostridium tetani produces tetanospasmin toxin, which affects the nervous system but does not inhibit protein synthesis. Choice D: Staphylococcus aureus produces toxins like enterotoxins and exotoxins but these toxins do not directly inhibit protein synthesis.

Correct Answer: C

Rationale: The correct answer is C: urethra. Resident microflora refers to the normal, beneficial bacteria that inhabit a specific area of the body without causing harm. The urethra is one of the locations where resident microflora are commonly found. These bacteria play a vital role in maintaining a healthy balance and preventing harmful pathogens from colonizing the urethra. Blood (A), lung (B), and cerebro-spinal fluid (D) are not typical locations for resident microflora as these areas are usually sterile or have very limited microbial presence to prevent infections.