Enteric bacteria cross-reactive with Neisseria meningitidis groups A and C and Diplococcus pneumoniae types I and 3.

Enteric bacteria of 1,335 individual strains were studied for serological cross-reactions with Neisseria meningitidis groups A and C and Diplococcus pneumoniae types I and III. Enterobacterial antigens cross-reactive with the capsular polysaccharides of these four bacteria were found. Bacteria cross-reactive with noncapsular antigens of meningococci and pneumococci were also observed. Since some enteric bacteria possess antigens with serological specificities similar to those of meningococci, the possibility that enteric bacteria cross-reactive with meningococcal antigens provide an antigenic stimulus for the observed age-related "natural" immunity to this pathogen is discussed.