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Which of the following bacteria is responsible for causing the disease tetanus?
- A. Clostridium tetani
- B. Clostridium perfringens
- C. Streptococcus pyogenes
- D. Escherichia coli
Correct Answer: A
Rationale: The correct answer is A: Clostridium tetani. This bacterium is responsible for causing tetanus due to its production of tetanus toxin. Clostridium perfringens (B) causes gas gangrene, Streptococcus pyogenes (C) causes strep throat and skin infections, and Escherichia coli (D) is a common gut bacteria that can cause food poisoning but not tetanus.
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Microscopic analysis of dental plaque revealed flagellated protozoa without a cyst stage. What microorganism is likely present?
- A. Trichomonas tenax
- B. Entamoeba gingivalis
- C. Balantidium coli
- D. Giardia lamblia
Correct Answer: A
Rationale: The correct answer is A: Trichomonas tenax. Trichomonas tenax is a flagellated protozoan commonly found in the oral cavity and does not have a cyst stage. This organism typically inhabits the gingival crevices and can be identified in dental plaque samples. Entamoeba gingivalis (B) is an amoeba and does not have flagella. Balantidium coli (C) is a ciliated protozoan that infects the intestines, not the oral cavity. Giardia lamblia (D) is a flagellated protozoan that infects the intestines and has a distinct cyst stage. Therefore, the presence of flagellated protozoa without a cyst stage in dental plaque indicates Trichomonas tenax is likely present.
A patient with acute food poisoning had fecal cultures grown on Endo agar, resulting in colorless colonies. What microorganism is most likely responsible?
- A. Salmonella
- B. Escherichia coli
- C. Staphylococcus
- D. Shigella
Correct Answer: A
Rationale: Step 1: Endo agar is a selective and differential media commonly used to isolate gram-negative bacteria.
Step 2: Colorless colonies on Endo agar indicate the absence of lactose fermentation.
Step 3: Salmonella is a gram-negative bacterium that does not ferment lactose, leading to colorless colonies on Endo agar.
Step 4: Therefore, the correct answer is A: Salmonella.
Summary:
B: Escherichia coli ferments lactose, producing pink colonies on Endo agar.
C: Staphylococcus is a gram-positive bacterium and would not grow on Endo agar.
D: Shigella is a gram-negative bacterium but ferments lactose, resulting in pink colonies on Endo agar.
Microscopy of stained (Ziehl-Neelsen staining) smears taken from the sputum of a patient with chronic pulmonary disease revealed red bacilli. What property of tuberculous bacillus was shown up?
- A. Acid resistance
- B. Alkali resistance
- C. Alcohol resistance
- D. Capsule formation
Correct Answer: A
Rationale: The correct answer is A: Acid resistance. Tuberculous bacilli are acid-fast bacilli, meaning they resist decolorization by acid-alcohol after staining with Ziehl-Neelsen stain. This property is due to the high lipid content in the cell wall of Mycobacterium tuberculosis. Alkali resistance (B) and alcohol resistance (C) are not specific properties of tuberculous bacilli. Capsule formation (D) is a characteristic of some bacteria but is not a defining feature of tuberculous bacilli.
A 47-year-old male patient consulted a dentist about difficult mouth opening (lockjaw or trismus). The patient has a history of a stab wound of the lower extremity. What infection can be manifested by these symptoms?
- A. Tetanus
- B. Brucellosis
- C. Whooping cough
- D. Anaerobic wound infection
Correct Answer: A
Rationale: The correct answer is A: Tetanus. Tetanus is caused by the bacterium Clostridium tetani, commonly found in soil, dust, and animal feces. The patient's history of a stab wound increases the risk of tetanus infection as the bacterium can enter the body through the wound. Tetanus infection can lead to symptoms such as lockjaw or trismus, which are characterized by muscle stiffness and difficulty opening the mouth. This is due to the neurotoxin produced by Clostridium tetani affecting the muscles.
Summary of incorrect choices:
B: Brucellosis is a bacterial infection transmitted from animals to humans through consumption of unpasteurized dairy products. It does not typically manifest with symptoms of lockjaw.
C: Whooping cough (Pertussis) is a respiratory infection caused by Bordetella pertussis bacteria. It presents with severe coughing fits but does not cause lockjaw.
D: Anaerobic wound infection
Which of the following bacteria can cause meningitis?
- A. Neisseria meningitidis
- B. Haemophilus influenzae
- C. Streptococcus pneumoniae
- D. All of the above
Correct Answer: D
Rationale: The correct answer is D, "All of the above." Neisseria meningitidis, Haemophilus influenzae, and Streptococcus pneumoniae are all bacteria known to cause meningitis. Neisseria meningitidis is a common cause of bacterial meningitis in young adults, Haemophilus influenzae type b is a common cause in children, and Streptococcus pneumoniae is a leading cause in adults and the elderly. Therefore, all three bacteria can potentially cause meningitis depending on the age group and other factors. The other choices are incorrect because each of the bacteria listed can cause meningitis, so selecting only one of them would be incorrect.