Characterization of Shigella type 1 fimbriae: expression, FimA sequence, and phase variation

Abstract

This study documents the presence of type 1 fimbriae on Shigella and confirms these mannose-sensitive adherence structures to be bona fide components of the Shigella surface. While laboratory-passaged Shigella strains and lyophilized clinical isolates failed to express type 1 fimbriae, 6 of 20 recent clinical isolates, including 4 Shigella flexneri strains, 1 Shigella boydii strain, and 1 Shigella dysenteriae strain, produced type 1 fimbriae as detected by mannose-sensitive hemagglutination (MSHA) and electron microscopy. Optimal production of a predominantly Fim ؉ population required serial passage every 48 to 72 h in unshaken brain heart infusion broth at 37°C. Fim ؉ Shigella cultures were capable of reversibly switching to a non-MSHA, afimbriated phase during serial aerobic cultivation on tryptic soy agar plates. The amino acid sequence of S. flexneri type 1 FimA contained 18 substitutions compared to that of Escherichia coli fimbrillin. Indirect immunoelectron microscopy suggested the presence of both shared and unique epitopes on E. coli and S. flexneri type 1 fimbriae. Random phase variation between fimbriated and afimbriated states in Shigella was accompanied by the genomic rearrangement associated with phase variation in E. coli.

Shigella flexneri adherence factor expression in in vivo-like conditions

“…We next performed mutational analyses of the genes encoding major structural subunits to demonstrate functional roles in biofilm formation and epithelial cell adherence. We concentrated our analyses on long polar fimbriae representing the thick appendages, type 1 fimbriae representing the thin hair-like structures, and curli representing the electron dense, cloud-like aggregates based on our in silico analyses, the combined appearance of structures in Figures 1 and 2, and the known functional roles of these structures in initial biofilm formation and epithelial cell adherence in other pathogens (8, 28, 43–45). Thus, we constructed ΔlpfA, ΔfimA , and ΔcsgA mutants.…”

“…For type 1 fimbriae, previous studies support our observations of both fimA gene transcription and soluble FimA expression. First, clinical isolates of Shigella produced fimbrial-like adhesins after periods of prolonged static growth; however, the genes encoding the factors were not identified (28). Second, another RNA-seq study detected significant induction of the type 1 fim operon in a ΔicgR mutant of S. flexneri 2457T during the intracellar phase of the Shigella lifestyle (60).…”

Validation of growth as measurand for bacterial adhesion to food and feed ingredients

“…The Salmonella strains employed were cultured and serially passaged in tubes with BHI medium under aerobic, static conditions to selectively enrich type 1‐fimbriated cells as described by Old and Duguid (1970) and Snellings et al. (1997).…”

“…Typhimurium ATCC 13311 were cultured in unshaken BHI broth (brain–heart infusion broth; Difco Laboratories, Detroit, MI, USA) at 37°C. Cultures were serially passaged every 24 h, at least five times, according to Old and Duguid (1970) and Snellings et al. (1997).…”

Identification and Molecular Analysis of Rough-Colony-Specific Outer Membrane Proteins of Actinobacillus actinomycetemcomitans

“…Multiple colony morphologies are seen in other pathogenic organisms and may be considered a form of phase variation (29). The expression of surface proteins of many gram-negative bacteria, including the opacity protein (OapA) of Haemophilus influenzae, the opacity and fimbrial proteins of Neisseria gonorrhoeae and Neisseria meningitidis, and the type 1 fimbriae of Escherichia coli and other enteric species, are known to phase vary (13,36,50,60,62,66). However, unlike the rapid reversal of phenotype typical in other organisms, the colonial morphology shift in A. actinomycetemcomitans has rarely been observed in vitro to change from the smooth to the rough colony phenotype (6,24,35,39,46,66).…”