microbiology chapter 14 test bank

Correct Answer: A

Rationale: The correct answer is A because Staphylococcus aureus can develop resistance to penicillin over time due to the production of beta-lactamase enzymes. This resistance mechanism makes it no longer susceptible to penicillin. The other choices are correct: B) S. aureus can produce beta hemolysis, C) it produces various toxins like hemolysins, leucocidins, and enterotoxins, and D) it shows a positive catalase reaction due to the presence of catalase enzyme that converts hydrogen peroxide to water and oxygen.

Correct Answer: B

Rationale: The correct answer is B: Azotobacter species. Azotobacter are known for their ability to fix nitrogen through the process of nitrogen fixation, converting atmospheric nitrogen into a form that plants can use. Bacillus cereus is not known for nitrogen fixation. Clostridium botulinum is a bacterium that causes botulism and does not fix nitrogen. Escherichia coli is a common gut bacterium but does not have the ability to fix nitrogen. Thus, Azotobacter species is the correct choice based on its unique ability to fix nitrogen.

Correct Answer: B

Rationale: The correct answer is B: plasma coagulase. This enzyme is essential for the pathogenicity of Staphylococcus aureus as it can convert fibrinogen to fibrin, forming a protective barrier around the bacteria. This helps the bacteria evade the host's immune system. Beta lactamase (A) is not directly related to pathogenicity but rather resistance to beta-lactam antibiotics. Catalase (C) is produced by many bacteria, including Staphylococcus aureus, but it is not a specific indicator of pathogenicity. Choice D is incorrect as plasma coagulase is indeed an important criterion for the pathogenicity of Staphylococcus aureus.

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.