Mycobacterium tuberculosis is

Correct Answer: D

Rationale: The correct answer is D because Mycobacterium tuberculosis is a straight or slightly curved rod with occasional polymorphism. This bacterium does not conform to the characteristics of gram-negative coccus (A), gram-positive coccus (B), or gram-negative rod (C). Mycobacterium tuberculosis is characterized by its unique cell wall composition, which includes high lipid content and mycolic acids, contributing to its acid-fast staining property. The other choices are incorrect because they do not accurately describe the morphology of Mycobacterium tuberculosis.

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: A

Rationale: The correct answer is A: Acid resistance. Tuberculosis mycobacteria have a unique cell wall structure that makes them resistant to acid-fast staining methods like Ziehl-Neelsen. This is due to the high lipid content of their cell walls, specifically mycolic acids, which prevent the penetration of stains and acids. The red bacilli observed in the smear indicate that the mycobacteria retained the primary stain (carbolfuchsin) after acid-alcohol decolorization, confirming their acid resistance. Summary: - Choice A: Acid resistance is correct due to the unique cell wall structure of tuberculosis mycobacteria. - Choice B: Alkali resistance is incorrect as mycobacteria are not known for being resistant to alkalis. - Choice C: Alcohol resistance is incorrect as mycobacteria are not specifically resistant to alcohols. - Choice D: Encapsulation is incorrect as mycobacteria are not encapsulated bacteria.

Correct Answer: B

Rationale: The correct answer is B: Conjugation. Conjugation involves the transfer of genetic material from a donor cell to a recipient cell through direct cell-to-cell contact, typically mediated by a conjugative plasmid. During conjugation, a conjugative pilus forms a bridge between the donor and recipient cells, allowing the transfer of genetic material. A: Replication is the process of copying DNA to produce two identical DNA molecules. It does not involve the transfer of genetic material between cells. C: Transformation is the uptake and incorporation of foreign DNA from the environment by a bacterial cell. It does not require direct cell-to-cell contact. D: Transduction is the transfer of genetic material from one bacterium to another by a bacteriophage vector. It does not involve direct cell-to-cell contact between the donor and recipient cells.

Correct Answer: A

Rationale: The correct answer is A because differential growth media, such as Endo agar and MacConkey agar, contain specific indicators or substrates that allow for the differentiation of microorganisms based on their metabolic properties. For example, Eosin methylene blue agar differentiates between lactose fermenting and non-fermenting bacteria based on color changes. Levine's formulation is selective for Gram-negative bacteria due to bile salts and crystal violet. In contrast, the other choices do not have specific indicators for differentiation among microorganisms. Lowenstein-Jensen and SS agar are selective media for mycobacteria and Salmonella/Shigella species, respectively. ACA and BPLS agar are selective but not differential, and Nutrient agar and Peptone water are general-purpose media without differential properties.

Correct Answer: A

Rationale: The most likely diagnosis is Actinomycosis. This is because the patient's presentation of a painful swelling with a fistula containing white granules and yellow-green honeycomb-like tissue is classic for Actinomycosis. Actinomyces is a gram-positive anaerobic bacterium that forms sulfur granules in tissues. Tuberculosis (B) typically presents with caseating granulomas, not sulfur granules. Leprosy (C) presents with skin lesions and nerve damage, not characteristic of this case. Syphilis (D) usually presents with painless ulcers and rash, not the painful swelling and fistula seen in this patient.

Correct Answer: A

Rationale: The correct answer is A: Corynebacterium diphtheriae. This bacterium causes diphtheria, characterized by a grayish pseudomembrane in the throat. The dark blue-staining rods with polar granules seen in microscopic examination are known as metachromatic granules, which are specific to Corynebacterium diphtheriae. Streptococcus pyogenes (choice B) causes strep throat but does not produce pseudomembranes. Haemophilus influenzae (choice C) can cause respiratory infections but does not typically present with a pseudomembrane. Neisseria gonorrhoeae (choice D) is a sexually transmitted bacterium and is not associated with the symptoms described.

Correct Answer: D

Rationale: The correct answer is D because all three bacteria - Salmonella enterica, Clostridium botulinum, and Escherichia coli - are commonly associated with foodborne illnesses. Salmonella causes gastroenteritis, Clostridium botulinum causes botulism, and E. coli can lead to severe food poisoning. Each bacterium has different mechanisms of causing illness, but all can be transmitted through contaminated food. Choices A, B, and C alone are incorrect because they do not encompass the full spectrum of bacteria commonly linked to foodborne illnesses.

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.