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free microbiology test bank questions pdf Questions
Question 1 of 9
Bacteria that grow best in high temperatures are called:
Correct Answer: C
Rationale: The correct answer is C: Thermophiles. Thermophiles are bacteria that thrive in high temperatures, typically between 45-80 degrees Celsius. They have adapted to extreme heat environments and have enzymes that function optimally at high temperatures. Mesophiles (A) grow best at moderate temperatures, Psychrophiles (B) thrive in cold temperatures, and Halophiles (D) thrive in high salt concentrations. Therefore, only Thermophiles are specifically adapted to high temperatures, making it the correct choice.
Question 2 of 9
Which bacteria are known for causing food poisoning due to their production of enterotoxins?
Correct Answer: D
Rationale: The correct answer is D, "All of the above." Clostridium botulinum produces botulinum toxin causing botulism. Salmonella enterica can produce enterotoxins causing food poisoning. Staphylococcus aureus also produces enterotoxins leading to food poisoning. Therefore, all three options can cause food poisoning due to their production of enterotoxins.
Question 3 of 9
Microscopic examination of dental plaque revealed unicellular organisms with two layers in their cytoplasm and wide pseudopodia. What is the likely causative agent?
Correct Answer: A
Rationale: Rationale: 1. Unicellular organisms with two layers in cytoplasm = Entamoeba gingivalis. 2. Wide pseudopodia = characteristic of Entamoeba genus. 3. Entamoeba histolytica causes amoebic dysentery, not dental plaque. 4. Trichomonas tenax causes periodontal disease, not dental plaque. 5. Lamblia intestinalis causes giardiasis, not related to dental plaque.
Question 4 of 9
Streptococci are:
Correct Answer: D
Rationale: The correct answer is D because Streptococci are Gram-positive bacteria, typically spherical in shape, and range from 0.5-1 µm in size. A is incorrect as streptococci are not rod-shaped and are usually smaller in size. B is incorrect as they are not Gram-negative and are not typically of such small size. C is incorrect as streptococci are not Gram-negative and are not usually rod-shaped. Thus, based on their characteristics, the correct answer is D.
Question 5 of 9
The movement of molecules through a membrane from an area of high hydrostatic pressure to an area of lower hydrostatic pressure is:
Correct Answer: D
Rationale: The correct answer is D: simple diffusion. In simple diffusion, molecules move from an area of high concentration to low concentration without the need for energy input. Hydrostatic pressure is a form of passive transport that drives molecules to equalize concentration. Filtration (A) involves the movement of solutes through a membrane under pressure. Exocytosis (B) is the process by which cells release substances outside the cell using energy. Osmosis (C) is the movement of water molecules across a selectively permeable membrane. Therefore, simple diffusion is the most appropriate choice in this scenario.
Question 6 of 9
How soon do symptoms typically appear after a person is infected with rabies virus
Correct Answer: D
Rationale: The correct answer is D: 1-2 years. Rabies has a long incubation period before symptoms appear due to the slow progression of the virus within the body. The virus travels along nerve fibers to the brain, which can take months to years. During this time, the virus replicates and spreads, eventually leading to symptoms. Choices A, B, and C are incorrect as they underestimate the incubation period of rabies. Symptoms typically do not appear as early as 48 hours, 1 week, or 1 month after infection with the rabies virus.
Question 7 of 9
In which of the following GIT infections, the bacteria adhere to the intestine wall and damage the microvilli:
Correct Answer: A
Rationale: The correct answer is A: Enteropathogenic E. Coli (EPEC). EPEC bacteria adhere to the intestine wall using a protein called intimin, leading to microvilli damage. This attachment disrupts the normal absorption function of the intestine. Summary of why other choices are incorrect: B: Enterohemorrhagic E. Coli (EHEC) primarily causes bloody diarrhea and does not specifically target microvilli. C: Enterotoxigenic E. Coli (ETEC) produces toxins that lead to watery diarrhea but does not directly target microvilli. D: Enteroinvasive E. Coli (EIEC) invades and replicates within intestinal cells, causing inflammatory diarrhea, but does not specifically damage microvilli.
Question 8 of 9
A child with diarrhea had stool microscopy revealing cysts with four nuclei. What is the most likely causative agent?
Correct Answer: A
Rationale: The correct answer is A: Entamoeba histolytica. This pathogen is known to cause amoebic dysentery, characterized by diarrhea with bloody or mucoid stools. The presence of cysts with four nuclei in the stool microscopy is a characteristic feature of Entamoeba histolytica. Other choices are incorrect because Giardia lamblia typically presents with binucleate cysts, Balantidium coli is a ciliated protozoan, and Trichomonas hominis is a non-pathogenic parasite found in the human intestine.
Question 9 of 9
A patient suffering form tuberculosis was treated with rifampicin, which caused drug resistance of tuberculosis mycobacteria. In order to reduce mycobacteria resistance, rifampicin should be combined with the following drug:
Correct Answer: A
Rationale: The correct answer is A: Isoniazid. When rifampicin is used alone, there is a risk of developing resistance. Isoniazid is commonly used in combination with rifampicin to prevent resistance by targeting different mechanisms in the bacteria. Isoniazid works by inhibiting mycolic acid synthesis, while rifampicin targets RNA polymerase. This combination therapy is known as the first-line treatment for tuberculosis. Choices B, C, and D are incorrect because they do not have the same mechanism of action as isoniazid and would not be effective in preventing rifampicin resistance.