Mastering Microbiology Test Bank

Correct Answer: A

Rationale: Rationale for Correct Answer (A: Fluconazole): Fluconazole is an antifungal medication used to treat yeast infections caused by Candida albicans. It targets the fungal cell membrane, disrupting its structure and function. This makes it an effective treatment for oral thrush, which is caused by Candida overgrowth in the oral mucosa. The continuous use of antibiotics can disrupt the normal balance of microorganisms in the body, leading to fungal overgrowth. Fluconazole specifically targets the yeast fungi without affecting bacteria, making it the appropriate choice for this complication. Summary of Incorrect Choices: B: Biseptol - Biseptol is an antibiotic that targets bacteria, not fungi like Candida albicans. C: Tetracycline - Tetracycline is also an antibiotic that targets bacteria, not fungi. D: Furazolidone - Furazolidone is an antibiotic primarily used for treating bacterial infections, not fungal infections like oral thrush caused by Candida

Correct Answer: A

Rationale: The correct answer is A: evade host immune responses. Antigenic variation allows bacteria to change their surface antigens, making it difficult for the host immune system to recognize and attack them effectively. This enhances the bacteria's ability to evade immune responses and establish infection. B: Increase antibiotic susceptibility is incorrect because antigenic variation does not directly impact the susceptibility of bacteria to antibiotics. C: Increase peptidoglycan synthesis is incorrect because antigenic variation is not related to the synthesis of peptidoglycan, which is a major component of the bacterial cell wall. D: Enhance motility is incorrect because antigenic variation does not directly affect the motility of bacteria. In summary, antigenic variation in bacteria primarily serves to help them evade host immune responses, making option A the correct answer.

Correct Answer: A

Rationale: The correct answer is A: Kitt-Tarozzi medium. This medium is specifically designed to culture Clostridium species, the causative agents of gas gangrene. Clostridium species are gram-positive bacilli that produce gas during their metabolism. Inoculating the material into Kitt-Tarozzi medium allows for the selective growth of Clostridium species, aiding in the confirmation of a gas gangrene diagnosis. Other choices are incorrect: B: Endo agar is used for the isolation of gram-negative enteric bacteria. C: Meat-peptone agar is a general-purpose medium and not specific for Clostridium species. D: Levine agar is used for the isolation of Salmonella and Shigella species, not Clostridium.

Correct Answer: B

Rationale: The correct answer is B: Cell-wall regrowth. This is not a bacterial antibiotic resistance mechanism because antibiotics target specific components in bacteria, such as cell wall synthesis, making regrowth impossible in the presence of antibiotics. Reduced permeability (A) decreases antibiotic entry, Over-expression of target (C) reduces antibiotic effectiveness, and Efflux pump (D) actively removes antibiotics from the cell, all contributing to antibiotic resistance. In summary, cell-wall regrowth is not a mechanism of antibiotic resistance, unlike the other choices that actively promote bacterial survival against antibiotics.

Correct Answer: D

Rationale: The correct answer is D, All of the above. Clostridium botulinum produces botulinum toxin causing botulism, Vibrio cholerae produces cholera toxin leading to severe diarrhea, and certain strains of Escherichia coli produce toxins causing gastrointestinal illness. Each bacterium has specific exotoxins that can result in severe gastrointestinal symptoms. Therefore, all three choices are correct in producing exotoxins that can cause severe gastrointestinal illness.