Association of virulence of Neisseria meningitidis with transparent colony type and low-molecular-weight outer membrane proteins.

To assess the factors that might be associated with the virulence of Neisseria meningitidis, isolates from the blood or cerebrospinal fluid of patients with meningococcal disease and meningococcal isolates from the nasopharynx of asymptomatic carriers were compared with regard to opacity or transparency of colonies. Neisseria meningitidis isolated from patients with meningitis and septicemia grew in predominantly transparent colonies, whereas meningococci isolated from asymptomatic carriers generally formed opaque or a mixture of opaque and transparent colonies. Piliated meningococci from opaque colonies attached to human mucosal cells in significantly greater numbers than did piliated meningococci from transparent colonies of the same isolate. Meningococci from transparent colonies were more resistant to killing by normal human serum than were meningococci from isogenic opaque colonies. Disease-associated isolates that formed transparent colonies contained one or more heat-modifiable outer membrane proteins of molecular weight 26,000-32,000 which were not found in some isogenic clones that formed opaque colonies. Transparency of meningococcal colonies may be an important marker for factors that mediate meningococcal virulence.