Variation in the protein and lipopolysaccharide composition of the meningococcal outer membrane may be due to either serotype differences or to changes in cultural conditions. There are 12 antigenically distinct serotypes of group B meningococci, and these are associated with distinct major outer membrane protein patterns on sodium dodecyl sulfate-polyacrylamide gels. In most strains the predominant outer membrane protein carries the serotype-specific determinant. Certain strains, when grown under similar conditions in different media, showed an altered membrane composition. The type 2 strain, M986, grown in modified Frantz medium-A, had a reduced amount of the major 41,000-dalton protein while a 28,000-dalton protein predominated. The altered protein composition may be related to changes in cell metabolism as reflected by the pH of the medium after growth. Growth of the organism in Frantz medium-B caused a negligible drop in pH and the 41,000-dalton protein remained predominant. There was also variation associated with changes in the growth rate. Increasing the aeration caused a concomitant increase in growth rate and cell yield. We observed two quantitative changes in outer membrane proteins in four of seven strains examined: (i) where only a single major protein changed (three strains), and (ii) where an increase in one protein component was associated with a decrease in another protein (one strain). When the strains were grown in tryptic soy broth (Difco Laboratories, Detroit, Mich.) with either high or low aeration, the total protein in the outer membrane remained constant. In contrast, with high aeration there was a significant increase in lipopolysaccharide. These studies suggest that the cell surface proteins may be altered by the organism to meet a variety of environmental conditions.

While effective polysaccharide vaccines have been developed for meningococcal groups A and C (15, 25), no such vaccine exists for group B (26). Group B is now a major cause of meningococcal disease in the United States (17) and abroad. Group B meningococci have been subdivided, as have group C, into several distinct serotypes (9, 12) based upon the presence of protein serotype antigens located in the outer membrane (11). The majority of both group B and group C disease is caused by a single serotype, type 2 (9, 13, 20). The type 2 antigens of groups B and C are chemically and serologically identical (11,20). Antibodies against the serotype antigens are bactericidal in the presence of complement (7), and the majority of bactericidal antibody in the sera of rabbits immunized with group B is directed against the serotype antigen (18).Study of meningococcal infection has been hampered by the absence of a useful laboratory model, since most common laboratory animals, including germ-free animals (19), are resistant to meningococcal challenge. The developing chicken embryo is one of the few laboratory animals readily susceptible to meningococcal infection. Following challenge, 9-15-day-old chick embryos develop lesions typical of meningococcal infection in man such as meningitis, sinusitis, and pulmonary infection (3,4,23). Ueda et al. (24) have developed a chick embryo model for the study of serum protection against group A meningococci. For intravenous (i.v.) challenge of 12-day-old embryos, they found that best protection was obtained when diluted serum was injected simultaneously with the bacterial challenge. Based upon the work of Ueda et al. (24), we have used the chick embryo model to investigate the role of type-specific and groupspecific antibodies in protection against group B meningococcal infection. Materials and MethodsBacterial Strains and Growth Conditions. The group B strains M986, M981, and M136 were characterized by Frasch and Chapman (7,8). The group B type 2 strain $946 was received from Dr.