Monitoring the genotype of meningococcal strains during an endemic period

ObjectiveTo monitor the circulation of clones among the most frequent phenotypes of Neisseria meningitidis isolated from sporadic cases in Italy in recent years.MethodsN. meningitidis strains sent to the reference laboratory for meningococcal meningitis of the istituto Superiore di Sanità were typed for serogroup, serotype and serosubtype, and chromosomal DNAs were analyzed by pulsed-field gel electrophoresis.ResultsOf 185 strains sent during the years 1995–97, 75% belonged to serogroup B. Although many different serotypes and subtypes were present, the most common combinations were B:14:P1.13, B:4:P1.13, B:15:P1.7 and C:2b:P1.2. PFGE analysis of patterns obtained by using NheI and Bg/II enzymes showed a quite stable genomic structure, except in the phenotype B:4:P1.13.ConclusionsOn the basis of serotype and serosubtype analysis of recently isolated meningococci, a great variety of phenotypes has been circulating during these endemic years. A clonal structure in strains belonging to the same phenotypes was found, suggesting that some favorable conditions have led to stability of these highly transmissible strains