Multilocus genotypes determined by enzyme electrophoresis of Neisseria meningitidis isolated from patients with systemic disease and from healthy carriers.

Variation in nine enzymes in 152 isolates of Neisseria meningitidis from Norway (118 from blood or cerebrospinal fluid of patients with systemic disease and 34 from the pharynx of healthy carriers) was analysed by starch-gel electrophoresis. All nine enzymes were polymorphic and the number of allozymes (electromorphs) identified per locus ranged from 3 to 12, with a mean of 6.1. Among the 152 isolates, 55 unique combinations of electromorphs (electrophoretic types, ETs) were distinguished. Twenty ETs were represented among the carrier isolates and 37 among the systemic isolates; hence, only two ETs were found in both groups of isolates. ET-5 was identified 67 times among the 118 systemic isolates (58%), indicating an association of this ET with invasiveness; ET-5 was also the most common type among the carrier isolates (18%). Genetic similarity between ETs was analysed by pairwise comparison of all 55 ETs with respect to the number of electromorphs by which they differed. No evidence of a general genetic difference between carrier and case isolates was found. Two well-defined clusters of ETs were observed, each including one of the two most common ETs identified among the systemic isolates (ET-5 and ET-37), together with isolates differing from them only at one or two loci. All isolates of ET-5 and ET-37, as well as their closely related variants defined by the similarity matrix, were resistant to sulphonamide, independent of their antigenic characteristics and isolation site. The extensive allozyme variation among isolates of the same serogroup demonstrated the limited value of serogrouping as an epidemiological tool. All but one isolate of serotype 15:P1.16 were electrophoretically similar, as were all the 2a:P1.2 isolates. The 15:P1.15 isolates, however, were genetically heterogeneous. The distribution of alleles in genotypes identified among the systemic isolates indicated that genetic recombination may occur in natural populations of N. meningitidis.