Question:easy
A female presents with signs of meningitis. CSF shows gram-positive bacilli. The most likely organism is?
A female presents with signs of meningitis. CSF shows gram-positive bacilli. The most likely organism is?
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Gram-positive rods in CSF of a vulnerable host means Listeria.
Updated On: Jun 24, 2026
- Listeria
- Haemophilus influenzae
- Pneumococcus
- Pseudomonas
Show Solution
The Correct Option is A
Solution and Explanation
Solving this question is purely a Gram-stain pattern-matching exercise. The CSF shows gram-positive bacilli, so the answer must be an organism that appears as a gram-positive rod. Run each candidate through its true staining and shape: Listeria monocytogenes is a small gram-positive bacillus, Haemophilus influenzae is a tiny gram-negative coccobacillus, Streptococcus pneumoniae is a lancet-shaped gram-positive diplococcus, and Pseudomonas aeruginosa is a motile gram-negative bacillus. The only organism that is both gram-positive and a bacillus is Listeria. This fits clinically as well, because Listeria meningitis classically strikes vulnerable hosts such as pregnant women, neonates, the elderly, and those with impaired cell-mediated immunity, and it is acquired from contaminated dairy and processed foods. Supporting laboratory features include its end-over-end tumbling motility seen in a hanging-drop preparation at room temperature and its ability to multiply at 4 degrees Celsius. All of this confirms that the gram-positive bacillus causing this meningitis is Listeria. \[\boxed{\text{Listeria}}\]
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