Abstract
Pneumococci are commonly classed among the best examples of bacterial type-specificity. While cross-reactions frequently occur involving types 3 and 8 and less frequently other types, they have usually been considered from the standpoint of the cross-reacting antibodies that sometimes develop during immunization rather than from the standpoint of the antigenic type-multiplicity which causes them. 1 , 2
Several strains of pneumococci that conspicuously violate the prevailing conception of type-specificity have been isolated recently in this laboratory. Neufeld tests with sera of 3 different manufacturers show that each of these strains reacts with at least 3 type-specific sera.
Table I summarizes the reactions of 6 such strains. It will be noted that each strain shows somewhat greater capsular swelling with one serum (either type 29 or type 24) than with others. However, reaction is only slightly less with a second, and in some strains with a third, serum.
With the exception of the Hoge strain all 6 were isolated from 488 routine specimens submitted to this laboratory for typing between February 16 and April 3, 1940. Fifty-nine of these specimens were reported as containing more than one type of pneumococci, and 18 of them examined for the possible presence of multiple-reacting strains. From these the last 5 listed in Table I were recovered. There is reason for believing that such strains were present in 2 other specimens but escaped isolation.
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