If a quellung test was done on the following bacterial isolates, which one would you expect to be positive?
The quellung test determines the presence of bacterial capsules. Specific antibody is mixed with the bacterial suspension or with clinical material. The polysaccharide capsule-antibody complex is visible microscopically. The test is also termed capsular swelling. The capsules of S. pneumoniae as well as N. meningitidis, H. influenzae, and K. pneumoniae play a role in the pathogenicity of the organisms. These surface structures inhibit phagocytosis, perhaps by preventing attachment of the leukocyte pseudopod. C. diphtheriae, Enterobacter, and H. parainfluenzae are nonencapsulated.
S. pneumoniae
Enterobacter
Haemophilus parainfluenzae
C. diphtheriae
Bacteria