If a quellungs test was done on a bacterial isolate, 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. Also Know: Pneumococci are gram-positive lancet-shaped cocci arranged in pairs (diplococci) or sho chains . On blood agar they produce alpha-hemolysis. In contrast to viridans streptococci, they are lysed by bile or deoxycholate, and their growth is inhibited by optochin. Ref: Levinson W. (2012). Chapter 15. Gram-Positive Cocci. In W. Levinson (Ed),Review of Medical Microbiology & Immunology, 12e.
S.pneumoniae
Enterobacter
Haemophilus parainfluenza
C.diphtheriae