Gallstones play a significant role in Salmonella spp. gallbladder colonization and carriage.

Salmonella enterica serovar Typhi can colonize the gallbladder and persist in an asymptomatic carrier state that is frequently associated with the presence of gallstones. We have shown that salmonellae form bile-mediated biofilms on human gallstones and cholesterol-coated surfaces in vitro. Here, we test the hypothesis that biofilms on cholesterol gallbladder stones facilitate typhoid carriage in mice and men. Naturally resistant (Nramp1(+/+)) mice fed a lithogenic diet developed cholesterol gallstones that supported biofilm formation during persistent serovar Typhimurium infection and, as a result, demonstrated enhanced fecal shedding and enhanced colonization of gallbladder tissue and bile. In typhoid endemic Mexico City, 5% of enrolled cholelithiasis patients carried serovar Typhi, and bacterial biofilms could be visualized on gallstones from these carriers whereas significant biofilms were not detected on gallstones from Escherichia coli infected gallbladders. These findings offer direct evidence that gallstone biofilms occur in humans and mice, which facilitate gallbladder colonization and shedding.

Survival of Salmonella enterica serovar Typhimurium within late endosomal-lysosomal compartments of B lymphocytes is associated with the inability to use the vacuolar alternative major histocompatibility complex class I antigen-processing pathway.

Gamma interferon (IFN-gamma)-activated macrophages use an alternative processing mechanism to present Salmonella antigens to CD8(+) T lymphocytes. This pathway involves processing of antigen in a vacuolar compartment followed by secretion and loading of antigenic peptides to major histocompatibility complex class I (MHC-I) molecules on macrophage cell surface and bystander cells. In this study, we have shown that B lymphocytes are not able to process Salmonella antigens using this alternative pathway. This is due to differences in Salmonella enterica serovar Typhimurium-containing vacuoles (SCV) when comparing late endosomal-lysosomal processing compartments in B lymphocytes to those in macrophages. The IFN-gamma-activated IC21 macrophage cell line and A-20 B-cell line were infected with live or dead Salmonella enterica serovar Typhimurium. The SCV in B cells were in a late endosomal-lysosomal compartment, whereas SCV in macrophages were remodeled to a non-characteristic late endosomal-lysosomal compartment over time. Despite the difference in SCV within macrophages and B lymphocytes, S. enterica serovar Typhimurium survives more efficiently within the IFN-gamma-activated B cells than in activated macrophage cell lines. Similar results were found during in vivo acute infection. We determined that a lack of remodeling of late endosomal-lysosomal compartments by live Salmonella infection in B lymphocytes is associated with the inability to use the alternative MHC-I antigen-processing pathway, providing a survival advantage to the bacterium. Our data also suggest that the B lymphocyte late endosome-lysosome environment allows the expression of Salmonella virulence mechanisms favoring B lymphocytes in addition to macrophages and dendritic cells as a reservoir during in vivo infection.

Aislamiento de poblaciones de Serratia marcescens de origen clínico en dos institutos pediátricos / Isolation of populations of Serratia marcescens of clinical origin in two pediatrics institutions

Introudcción. Serratia marcescens es un patógeno oportunista en hospederos inmunocomprometidos y se asocia fundamentalmente a brotes intrahospitalarios con tasas de letalidad elevadas. El propósito del presente estudio fue tipificar 2 poblaciones de S. marcescens de origen clínico aisladas en 2 institutos pediátricos semejantes. Material y métodos. Se empleó el sistema de biotipificación propuesto por Grimont para la caracterización de 65 cepas del Hospital Infantil de México, originalmente clasificadas como Enterobacter sp y 35 cepas del Instituto Nacional de Pediatría aisladas en un brote intrahospitalario. Reesultados. El biogrupo más numeroso en ambas poblaciones fue el A 5/8 y de éste los biotipos A8a y A8b; se observaron variaciones en las proporciones de los biotipos identificados acordes al hospital de aislamiento, así como en los biotipos y patrones de resistencia a los antibióticos en cepas aisladas del mismo pacientes en muestras diferentes. Conclusiones. Del presente estudio se concluye que es importante que en los hospitales se realicen estudios epidemiológicos particulares de sus poblaciones de S. marcescens, pero es más importante aún que se lleve a cabo una correcta identificación de esta bacteria para valorar adecuadamente su importancia como patógeno oportunista en nuestro medio