Question:medium
The polysaccharide capsule of which of the following bacteria has NO role in its infectivity?
The polysaccharide capsule of which of the following bacteria has NO role in its infectivity?
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Three are classic capsulated invaders; one relies on toxins and adhesins.
Updated On: Jun 24, 2026
- Neisseria meningitidis
- Pneumococcus
- Bordetella pertussis
- Haemophilus influenzae
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The Correct Option is C
Solution and Explanation
Identify the three classic encapsulated pathogens, and the odd one out becomes the answer.
A polysaccharide capsule helps bacteria escape being engulfed by phagocytes, which is why capsulated organisms are so invasive. Three of the listed bacteria are textbook capsulated pathogens. $Neisseria$ $meningitidis$ relies on its capsule for virulence and uses it for serogrouping and vaccine design. $Streptococcus$ $pneumoniae$ depends on its capsule as its main virulence factor, the basis of its polysaccharide vaccines. $Haemophilus$ $influenzae$ type b is invasive because of its PRP polysaccharide capsule, which the Hib vaccine targets.
That leaves $Bordetella$ $pertussis$. Its disease-causing power comes from a battery of toxins and surface adhesins, including pertussis toxin, filamentous haemagglutinin, pertactin, adenylate cyclase toxin, and tracheal cytotoxin, rather than from a polysaccharide capsule. So a capsule plays no meaningful part in its infectivity.
Hence the answer is Bordetella pertussis.
\[\boxed{\text{Bordetella pertussis}}\]
A polysaccharide capsule helps bacteria escape being engulfed by phagocytes, which is why capsulated organisms are so invasive. Three of the listed bacteria are textbook capsulated pathogens. $Neisseria$ $meningitidis$ relies on its capsule for virulence and uses it for serogrouping and vaccine design. $Streptococcus$ $pneumoniae$ depends on its capsule as its main virulence factor, the basis of its polysaccharide vaccines. $Haemophilus$ $influenzae$ type b is invasive because of its PRP polysaccharide capsule, which the Hib vaccine targets.
That leaves $Bordetella$ $pertussis$. Its disease-causing power comes from a battery of toxins and surface adhesins, including pertussis toxin, filamentous haemagglutinin, pertactin, adenylate cyclase toxin, and tracheal cytotoxin, rather than from a polysaccharide capsule. So a capsule plays no meaningful part in its infectivity.
Hence the answer is Bordetella pertussis.
\[\boxed{\text{Bordetella pertussis}}\]
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