The normal chain length distribution of the O antigen is required for the interaction of Shigella flexneri 2a with polarized Caco-2 cells

Shigella flexneri causes bacillary dysentery in humans. Essential to the establishment of the disease is the invasion of the colonic epithelial cells. Here we investigated the role of the lipopolysaccharide (LPS) O antigen in the ability of S. flexneri to adhere to and invade polarized Caco-2 cells. The S. flexneri 2a O antigen has two preferred chain lengths: a short O antigen (S-OAg) regulated by the WzzB protein and a very long O antigen (VL-OAg) regulated by Wzz pHS2. Mutants with defined deletions of the genes required for O-antigen assembly and polymerization were constructed and assayed for their abilities to adhere to and enter cultured epithelial cells. The results show that both VL- and S-OAg are required for invasion through the basolateral cell membrane. In contrast, the absence of O antigen does not impair adhesion. Purified LPS does not act as a competitor for the invasion of Caco-2 cells by the wild-type strain, suggesting that LPS is not directly involved in the internalization process by epithelial cells.

Ceftriaxone resistant Shigella Flexneri, an emerging problem.

Shigellosis is a disease of public health importance in developing countries. It may cause self-limited diarrhea to severe dysentery. Emergence of multi drug resistant (MDR) strains is a growing concern globally. Ceftriaxone and ciprofloxacin are the drugs of choice for MDR cases. Here, we report a case of MDR Shigella flexneri from an immunocompromised patient. The strain was resistant to ceftriaxone [minimum inhibitory concentration (MIC) ≥ 64 μg/ml], limiting the treatment option. Simultaneously, the strain was also found to be resistant to ciprofloxacin (MIC ≥ 4 μg/ml). However, it was susceptible to ceftazidime (MIC 4 μg/ml). This is the first case of ceftriaxone resistant Shigella spp. reported from our hospital.

Alterações na resposta imune inata e adaptativa induzidas por Escherichia coli enteroinvasora em modelo murino / Alterations in the innate immune response and adaptative induced by enteroinvasive Escherichia coli in model murine

Durante uma infecção, uma complexa seqüência de eventos é iniciada após a invasão do hospedeiro por microrganismos patogênicos. Escherichia coli enteroinvasora (EIEC), assim como Shigella, causa disenteria através da invasão da mucosa do cólon, levando à destruição tecidual e inflamação. Para que ocorra um processo infeccioso, porém, são necessários inóculos de `10 POT.2` Shigella e `10 POT.6` EIEC. Foram avaliados aspectos da resposta inflamatória desencadeada pela infecção por EIEC em modelo murino, comparativamente a Shigella. A infecção de macrófagos J774 por EIEC resultou em fagocitose bacteriana, comprometimento da viabilidade do macrófago e produção de citocinas. Macrófagos de camundongos C57BL/6 infectados com EIEC produziram NO, que parece ser importante no controle da infecção. Foi observado que camundongos INOS nocaute apresentaram maior produção de citocinas pró-inflamatórias e maior letalidade após infecção do que os selvagens. EIEC induziu a migração de granulócitos e monócitos para o peritônio, e a secreção de citocinas por estas células. Houve proliferação de linfócitos em resposta aos antígenos solúveis de EIEC, mas não foi detectada produção de citocinas por estes linfócitos. Comparativamente a Shigella, EIEC escapou mais lentamente do macráfago, induziu menor produção de citocinas pró-inflamatórias e NO, e menor ativação dos linfócitos T. Estes dados sugerem o desafio com EIEC desencadeia uma resposta menos severa no hospedeiro do que Shigella, o que explicaria a forma mais branda de disenteria e resolução mais rápida do processo infeccioso causado por EIEC.

Antibody response to outer membrane proteins in Shigella dysenteriae type 1 infection with special reference to appearance of murine antibodies.

In shigellosis, the protective immune mechanism is not well established. The bacterial outer membrane proteins (OMPs) may have a role in the induction of immunity due to their outwardly location. The serum antibody response of S. dysenteriae type 1 infected patients against OMPs was assessed by enzyme linked immunosorbent assay (ELISA). A striking elevation of serum IgG response was noted during the convalescent phase. Murine antiserum directed against S. dysenteriae 1 OMPs was found to be highly cross reactive with the OMPs isolated from heterologous species. A major antigenic OMP was partially purified and showed distinct immunodominance in ELISA. These observations suggest that the specific component may have some immunoprophylactic potential.

Vacunación contra la shigelosis / Vaccination against shigelosis

Se define como shigelosis a la enfermedad intestinal producida por las diferentes especies del género Shigella, de las cuales el humano es el principal hospedero. Shigella es un bacilo corto, Gram-negativo, de la familia Enterobacteriaceae. La shigelosis se manifiesta en tres formas: 1) disentería clásica (sangre, moco, pus), 2) diarrea acuosa no complicada y 3) una combinación de disentería y diarrea acuosa. La mayoría de los casos de diarrea acuosa no son distinguibles de las que son ocacionadas por otras etiologías. Concluye el documento enfatizando que, no existe hasta el momento actual ninguna vacuna contra Shigella que pueda ser recomendable para la aplicación en población general. Todos los esfuerzos hasta ahora realizados han quedado en pequeños estudios en voluntarios, en los cuales se han obtenido fracasos y en otros ensayos se han vislumbrado posibles vacunas para emplear en el futuro. Dentro de los modelos experimentales de vacunas que hasta el momento hay, se está intentando corregir los posibles errores y por otra parte conjuntar los mecanismos de acción propuestos para cada tipo de vacuna. Finalmente si la shigelosis es un problema de salud pública, principalmente en los países en vías de desarrollo, son importantes los esfuerzos para lograr obtener una vacuna que en lo futuro pueda reducir uno de los principales problemas de morbilidad infantil

Immunoblot analysis of antibody responses to Shigella dysenteriae type 1 infection.

Immunoblot analysis was used to identify the antigenic components of the outer membrane protein (OMP) extract from Sh. dysenteriae type 1 that may be relevant in protection against infection. The OMPs were extracted by ultrasonic disruption followed by Sarkosyl extraction. The macromolecular bands were separated by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), electroeluted to a nitrocellulose matrix and complexed with peroxidase conjugated antibodies in human convalescent sera. IgG specific reaction was found to a major antigenic component at 57 kilodaltons. In addition, weakly reactive three antigenic determinants of greater than 57 kD and four of less than 57 kD were found. Control sera from a rabbit immunized against OMP also exhibited a similar pattern of antigenic reactivity. Some of the OMPs with high antigenicity may be important in immunoprophylaxis.