microbiology chapter 11 test bank

Correct Answer: A

Rationale: Step-by-step rationale: 1. Clostridium botulinum is known for producing the neurotoxin causing botulism. 2. Botulinum toxin paralyzes muscles, leading to symptoms of botulism. 3. Clostridium tetani produces tetanus toxin causing muscle rigidity, not botulism. 4. Streptococcus pneumoniae causes pneumonia, not botulism. 5. Escherichia coli can cause food poisoning, but not botulism. Summary: Choice A is correct (Clostridium botulinum) due to its association with botulism and neurotoxin production. Choices B, C, and D are incorrect as they are associated with different diseases and toxins.

Correct Answer: A

Rationale: The correct answer is A: Staphylococcus aureus. This bacterium is characterized by Gram-positive cocci in clusters, catalase-positive, and coagulase-positive. Staphylococcus aureus is a common pathogen causing wound infections due to its ability to produce toxins and enzymes. Staphylococcus epidermidis (B) is catalase-positive but coagulase-negative, making it less likely to cause infections. Streptococcus pyogenes (C) is catalase-negative and typically causes streptococcal infections, not wound infections. Enterococcus faecalis (D) is catalase-negative and typically associated with urinary tract infections. Thus, Staphylococcus aureus is the most likely causative agent based on the given characteristics.

Correct Answer: A

Rationale: The correct answer is A: Metronidazole. Metronidazole is the drug of choice for amebic dysentery as it effectively targets the protozoa causing the infection. It has good tissue penetration and high efficacy against Entamoeba histolytica. Pyrantel (B) is used for nematode infections, not amebiasis. Levamisole (C) is an anthelmintic for roundworms and not effective against amoebas. Bicillin-5 (D) is a penicillin antibiotic, which is not indicated for treating amebic dysentery.

Correct Answer: D

Rationale: The correct answer is D: Salmonella typhi. Typhoid fever is caused by the bacterium Salmonella typhi. This bacterium is responsible for causing the systemic infection that leads to symptoms such as high fever, abdominal pain, and diarrhea. Yersinia pestis (choice A) causes plague, Shigella dysenteriae (choice B) causes dysentery, and Escherichia coli (choice C) can cause various gastrointestinal infections, but not typhoid fever. Salmonella typhi specifically targets the intestines and is transmitted through contaminated food or water. Therefore, choice D is the correct answer for the cause of typhoid fever.

Correct Answer: A

Rationale: The correct answer is A: Contaminated. The air is never completely free of microorganisms, so it is considered contaminated. Microorganisms are ubiquitous in the environment. Permissible limits (B) imply a specific standard, which is not relevant to the general microbiological characteristic of air. Almost pure (C) and pure (D) are not accurate as air always contains some level of microorganisms.