CHARACTERIZATION OF SHIGELLA TYPE-1 FIMBRIAE - EXPRESSION, FIMA SEQUENCE, AND PHASE VARIATION

This study documents the presence of type I fimbriae on Shigella and c onfirms these mannose-sensitive adherence structures to be bona fide c omponents of the Shigella surface, While laboratory-passaged Shigella strains and lyophilized clinical isolates failed to express type 1 fim briae, 6 of 20 recent clinical isolates, including 1 Shigella flexneri strains, 1 Shigella boydii strain, and 1 Shigella dysenteriae strain, produced type I fimbriae as detected by mannose-sensitive hemagglutin ation (MSHA) and electron microscopy. Optimal production of a predomin antly Fim(+) population required serial passage every 48 to 72 h in un shaken brain heart infusion broth at 37 degrees C, Fim(+) Shigella cul tures were capable of reversibly switching ro a non-MSHA, afimbriated phase during serial aerobic cultivation on tryptic soy agar plates, Th e amino acid sequence of S, flexneri type I FimA contained 18 substitu tions compared to that of Escherichia coli fimbrillin, Indirect immuno electron microscopy suggested the presence of both shared and unique e pitopes on E, coli and S, flexneri type 1 fimbriae. Random phase varia tion between fimbriated and afimbriated states in Shigella was accompa nied by the genomic rearrangement associated with phase variation in E , coli.