The lipopolysaccharide was extracted from S. dysenteriae 1 (NT4907) and S. flexneri 2a (B294) following the methods described by Slauch et al. (1995). The carbohydrate content of the lipopolysaccharide was estimated using the phenol–sulfuric acid method (Dubois et al., 1956). Analyses for the serum immunoglobulin G (IgG) antibody and mucosal IgA were performed using ELISA, following the method of Keren (1979). Test wells on polystyrene ELISA plates were coated (Nunc, Denmark) with 1 μg of the lipopolysaccharide in 100 μL of PBS. Control wells were coated with 100 μL of PBS only. After the completion of the assay,

the plate reading was taken at 492 nm wave length using an ELISA reader (Bio-Rad) and PBS control well readings were subtracted from the corresponding test well readings to yield the net NSC 683864 OD. For ELISA, the endpoint titer was the highest reciprocal dilution yielding a net OD of 0.100 or higher. Colonic specimens were carefully cut and the samples were fixed

in 10% neutral-buffered formalin, dehydrated in alcohol and embedded in paraffin. The sections were cut into 3 μm thickness and stained with hematoxylin and eosin. The slides were labeled and examined by a pathologist who was not aware of the experimental conditions. Analyzed data are presented as the mean±SE. Significant frequencies were compared using χ2-test and continuous variable was compared using the Student’s t-test. P values of <0.05 were considered statistically significant. A Sereny test was performed to confirm the virulent nature of the Shigella strains. The difference in pathogenicity between invasive and noninvasive strains Ruxolitinib mouse was demarcated by the severity of conjunctivitis. The development of keratoconjunctivitis with S. flexneri 2a (2457T), invasive S. dysenteriae 1 (NT4907) and S. flexneri 2a (B294) occurred 24 h after ocular inoculation, whereas avirulent strains (D1-vp and SB11-vp) did Rho not show any signs of keratoconjunctivitis even

after 96 h. In this study, 109 CFU of bacteria were used as it induced acute bacillary dysentery (Fig. 2a). Luminal inoculation with 2457T in guinea-pigs without cecal bypass did not result in successful bacterial colonization or diarrhea and the maximum level of colonization was ∼2 × 104 CFU g−1 (Fig. 2b). Guinea-pigs that received S. dysenteriae 1 (NT4907) and S. flexneri 2a (B294) by direct inoculation (109 CFU) into the cecocolic junction after ligation of the distal cecum were monitored for signs of dysentery at different time intervals (Fig. 3). Within 24 h of inoculation, all guinea-pigs infected with invasive wild-type Shigella strains developed symptoms identical to that of acute bacillary dysentery in humans (Fig. 3a), such as elevated rectal temperature (Fig. 3b), weight loss (Fig. 3c) and liquid stool containing mucus with or without blood. The guinea-pigs that were challenged with avirulent S. dysenteriae 1 (D1-vp) and S.