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

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 Astg 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-eukary-otic 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.

Salmonella enterica serovar Typhi plasmid pR ST98 -mediated inhibition of autophagy promotes bacterial survival in infected fibroblasts.

pR ST98 is a chimeric plasmid isolated from Salmonella enterica serovar typhi (S. typhi) and mediates both drug-resistance and virulence of S. typhi. Autophagy has been recently reported as an important component of the innate immune response against intracellular pathogen. In this study, we investigated the effect of pR ST98 on cellular autophagy, apoptosis and bacterial survival in infected fibroblasts. S. typhi strain ST 8 carrying pR ST98 , Salmonella typhimurium strain SR-11 carrying a 100 Kb virulent plasmid, and avirulent S. typhi strain ST 10 without plasmid were tested in this experiment. Results showed that embryonic fibroblasts infected with ST 8 containing pR ST98 had decreased autophagy accompanied by increased bacterial survival and apoptosis. Further study showed that autophagy inducer rapamycin reversed pR ST98 -mediated inhibition of autophagy and reduced apoptosis in infected fibroblasts. Our data indicate that pR ST98 can inhibit autophagy, thus facilitating S. typhi survival and promoting apoptosis of host cells. This study contributes to understanding the underlying mechanism of pR ST98 -mediated virulence in S. typhi.

Salmonella enterica serovar typhi plasmid pR ST98 enhances intracellular bacterial growth and S. typhi-induced macrophage cell death by suppressing autophagy

OBJECTIVES: Plasmid pR ST98 is a hybrid resistance-virulence plasmid isolated from Salmonella enterica serovar Typhi (S. typhi). Previous studies demonstrated that pR ST98 could enhance the virulence of its host bacteria. However, the mechanism of pR ST98-increased bacterial virulence is still not fully elucidated. This study was designed to gain further insight into the roles of pR ST98 in host responses. METHODS: Human-derived macrophage-like cell line THP-1 was infected with wild-type (ST8), pR ST98-deletion (ST8-ΔpR ST98), and complemented (ST8-c-pR ST98) S. typhi strains. Macrophage autophagy was performed by extracting the membrane-unbound LC3-I protein from cells, followed by flow cytometric detection of the membrane-associated fraction of LC3-II. Intracellular bacterial growth was determined by colony-forming units (cfu) assay. Macrophage cell death was measured by flow cytometry after propidium iodide (PI) staining. Autophagy activator rapamycin (RAPA) was added to the medium 2 h before infection to investigate the effect of autophagy on intracellular bacterial growth and macrophage cell death after S. typhi infection. RESULTS: Plasmid pR ST98 suppressed autophagy in infected macrophages and enhanced intracellular bacterial growth and S. typhi-induced macrophage cell death. Pretreatment with RAPA effectively restricted intracellular bacterial growth of ST8 and ST8-c-pR ST98, and alleviated ST8 and ST8-c-pR ST98-induced macrophage cell death, but had no significant effect on ST8-ΔpR ST98. CONCLUSIONS: Plasmid pR ST98 enhances intracellular bacterial growth and S. typhi-induced macrophage cell death by suppressing autophagy.

Compromiso hepático en fiebre tifoidea: Estudio bioquímico e histopatológico en pacientes anictéricos / Hepatic involvement typhoid fever: Biochemical and histopathological study in anicteric patients

El presente trabajo es un estudio prospectivo de 100 pacientes con diagnóstico de fiebre tifoidea mediante aislamiento de salmonella typhi. El procedimiento diagnóstico de mayor utilidad fue el mielocultivo, con un 90 por ciento de positividad. El compromiso hepático fue de presentación frecuente (85 por ciento), 67 pacientes fueron anictéricos y 18 pacientes cursaron con ictericia. Fueron sometidos a biopsia hepática 50 pacientes del grupo anictérico, de los cuales 50 por ciento mostraron hallazgos compatibles con hepatitis granulomatosa y el otro 50 por ciento, hepatitis reaccional. La respuesta al tratamiento antibiótico fue idéntica, en relación con los que no presentaron compromiso hepático.