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Background   Salmonella enterica  serovar Typhi ( S.  Typhi)  stg  operon, encoding a chaperone/usher fimbria (CU), contributes to an increased adherence to human epithelial cells. However, one report suggests that the presence of the Stg fimbria impairs the monocyte—bacteria association, as deduced by the lower level of invasion to macrophage-like cells observed when the  stg  fimbrial cluster was overexpressed. Nevertheless, since other CU fimbrial structures increase the entry of  S.  Typhi into macrophages, and considering that transcriptomic analyses revealed that  stg  operon is indeed expressed in macrophages, we reassessed the role of the  stg  operon in the interaction between  S.  Typhi strain STH2370 and human cells, including macrophage-like cells and mononuclear cells directly taken from human peripheral blood.    Results  We compared  S.  Typhi STH2370 WT, a Chilean clinical strain, and the  S.  Typhi STH2370 Δ stg  mutant with respect to association and invasion using epithelial and macrophage-like cells. We observed that deletion of  stg  operon reduced the association and invasion of  S.  Typhi, in both cellular types. The presence of the cloned  stg  operon restored the WT phenotype in all the cases. Moreover, we compared  Salmonella enterica  sv. Typhimurium 14028s ( S.  Typhimurium, a serovar lacking  stg  operon) and  S.  Typhimurium heterologously expressing  S.  Typhi  stg . We found that the latter presents an increased cell disruption of polarized epithelial cells and an increased association in both epithelial and macrophage-like cells.    Conclusions   S.  Typhi  stg  operon encodes a functional adhesin that participates in the interaction bacteria—eukaryotic cells, including epithelial cells and macrophages-like cells. The phenotypes associated to  stg  operon include increased association and consequent invasion in bacteria—eukaryotic cells, and cell disruption.    Electronic supplementary material  The online version of this article (doi:10.1186/s40659-015-0024-9) contains supplementary material, which is available to authorized users.

stg fimbrial operon from S. Typhi STH2370 contributes to association and cell disruption of epithelial and macrophage-like cells