deoxycholic-acid and Dysentery--Bacillary

Type three secretion systems (T3SS) are specialized nanomachines that support infection by injecting bacterial proteins directly into host cells. The Shigella T3SS has uniquely evolved to sense environmental levels of the bile salt deoxycholate (DOC) and upregulate virulence in response to DOC. In this study, we describe a rare i + 5 hydrogen bonding secondary structure element (π-helix) within the type three secretion system tip protein IpaD that plays a critical role in DOC-enhanced virulence. Specifically, engineered mutations within the π-helix altered the pathogen's response to DOC, with one mutant construct in particular exhibiting an unprecedented reduction in virulence following DOC exposure. Fluorescence polarization binding assays showed that these altered DOC responses are not the result of differences in affinity between IpaD and DOC, but rather differences in the DOC-dependent T3SS tip maturation resulting from binding of IpaD to translocator/effector protein IpaB. Together, these findings begin to uncover the complex mechanism of DOC-enhanced Shigella virulence while identifying an uncommon structural element that may provide a much needed target for non-antibiotic treatment of Shigella infection.

Topics: Bacterial Proteins; Bile Acids and Salts; Deoxycholic Acid; Dysentery, Bacillary; HeLa Cells; Host-Pathogen Interactions; Humans; Protein Structure, Secondary; Shigella flexneri; Type III Secretion Systems; Virulence

Shigella sonnei is a bacterial pathogen and causative agent of bacillary dysentery. It deploys a type III secretion system to inject effector proteins into host epithelial cells and macrophages, an essential step for tissue invasion and immune evasion. Although the arsenal of bacterial effectors and their cellular targets have been studied extensively, little is known about the prerequisites for deployment of type III secreted proteins during infection. Here, we describe a novel S. sonnei adhesin, SSO1327 which is a multivalent adhesion molecule (MAM) required for invasion of epithelial cells and macrophages and for infection in vivo. The S. sonnei MAM mediates intimate attachment to host cells, which is required for efficient translocation of type III effectors into host cells. SSO1327 is non-redundant to IcsA; its activity is independent of type III secretion. In contrast to the up-regulation of IcsA-dependent and independent attachment and invasion by deoxycholate in Shigella flexneri, deoxycholate negatively regulates IcsA and MAM in S. sonnei resulting in reduction in attachment and invasion and virulence attenuation in vivo. A strain deficient for SSO1327 is avirulent in vivo, but still elicits a host immune response.

Topics: Adhesins, Bacterial; Animals; Bacterial Proteins; Deoxycholic Acid; Disease Models, Animal; DNA-Binding Proteins; Dysentery, Bacillary; Epithelial Cells; Guinea Pigs; HeLa Cells; Humans; Keratoconjunctivitis; Larva; Macrophages; Moths; Shigella flexneri; Shigella sonnei; Transcription Factors; Type III Secretion Systems; Up-Regulation; Virulence

Following contact with the epithelium, the enteric intracellular bacterial pathogen Shigella flexneri invades epithelial cells and escapes intracellular phagosomal destruction using its type III secretion system (T3SS). The bacterium replicates within the host cell cytosol and spreads between cells using actin-based motility, which is mediated by the virulence factor IcsA (VirG). Whereas S. flexneri invasion is well characterized, adhesion mechanisms of the bacterium remain elusive. We found that IcsA also functions as an adhesin that is both necessary and sufficient to promote contact with host cells. As adhesion can be beneficial or deleterious depending on the host cell type, S. flexneri regulates IcsA-dependent adhesion. Activation of the T3SS in response to the bile salt deoxycholate triggers IcsA-dependent adhesion and enhances pathogen invasion. IcsA-dependent adhesion contributes to virulence in a mouse model of shigellosis, underscoring the importance of this adhesin to S. flexneri pathogenesis.

Topics: Animals; Antigens, Bacterial; Bacterial Adhesion; Bacterial Proteins; Bacterial Secretion Systems; Caco-2 Cells; Cell Line, Tumor; Cholagogues and Choleretics; Deoxycholic Acid; DNA-Binding Proteins; Dysentery, Bacillary; Epithelial Cells; HeLa Cells; Humans; Mice; Shigella flexneri; Transcription Factors

Shigella flexneri uses its type III secretion apparatus (TTSA) to inject host-altering proteins into targeted eukaryotic cells. The TTSA is composed of a basal body and an exposed needle with invasion plasmid antigen D (IpaD) forming a tip complex that controls secretion. The bile salt deoxycholate (DOC) stimulates recruitment of the translocator protein IpaB into the maturing TTSA needle tip complex. This process appears to be triggered by a direct interaction between DOC and IpaD. Fluorescence spectroscopy and NMR spectroscopy are used here to confirm the DOC-IpaD interaction and to reveal that IpaD conformational changes upon DOC binding trigger the appearance of IpaB at the needle tip. Förster resonance energy transfer between specific sites on IpaD was used here to identify changes in distances between IpaD domains as a result of DOC binding. To further explore the effects of DOC binding on IpaD structure, NMR chemical shift mapping was employed. The environments of residues within the proposed DOC binding site and additional residues within the "distal" globular domain were perturbed upon DOC binding, further indicating that conformational changes occur within IpaD upon DOC binding. These events are proposed to be responsible for the recruitment of IpaB at the TTSA needle tip. Mutation analyses combined with additional spectroscopic analyses confirm that conformational changes in IpaD induced by DOC binding contribute to the recruitment of IpaB to the S. flexneri TTSA needle tip. These findings lay the foundation for determining how environmental factors promote TTSA needle tip maturation prior to host cell contact.

Topics: Antigens, Bacterial; Bacterial Proteins; Binding Sites; Deoxycholic Acid; Dysentery, Bacillary; Fluorescence Resonance Energy Transfer; Host-Pathogen Interactions; Humans; Models, Molecular; Mutagenesis, Site-Directed; Nuclear Magnetic Resonance, Biomolecular; Protein Conformation; Shigella flexneri

Growth promoting properties and selectivity of 11 commercially produced media recommended for Salmonella and Shigella isolation were evaluated. The following media were tested: EMB (Eosin methylene blue agar), Endo, Płoskiriew, MacConkey, DC (Deoxycholate citrate agar), SS (Salmonella-Shigella agar), BS (Bismuth sulfite agar) and Mueller-Hinton as a medium with no selective properties. The media were produced in Czechoslovakia, East Germany, West Germany, Poland, and Soviet Union. Quantitative studies were performed on 71 strains representing 8 genera of Enterobacteriaceae family; both reference and wild newly + isolated from clinical material strains were included. It was found that none of DC and BS media provided suitable growth conditions for Shigella strains and in particular for S. dysenteriae, S. boydii, and S. flexneri. It was also found that the same medium (name and content) but derived from different producer can vary significantly in respect to growth promotion and selectivity especially for Shigella strains. All media with selective, differentiating properties for Salmonella and Shigella isolation should not be used without previous quantitative control test for their selective and growth promoting properties checked by user. The need for such a control performed both on reference and freshly isolated strains was shown in this study. In the set of control strains all species of Shigella should be represented.

Topics: Agar; Bismuth; Colony Count, Microbial; Culture Media; Deoxycholic Acid; Dysentery, Bacillary; Growth Substances; Humans; Salmonella; Salmonella Infections; Shigella; Temperature

The dynamics of the accumulation of phase II S. sonnei in the infectious process in germ-free rats, during cultivation and in subcultures was studied. The in vivo variability of S. sonnei showed a sharply defined phasic character of the process with the periods of the apparent absence of phase II, the increase of its occurrence and stabilization with the preservation of S-forms in minor amounts. Kanamycin-resistant phase II accumulated in vivo more rapidly than in vitro. Cultivation with sodium desoxycholate was found to accelerate the process of disassociation. The characteristic feature of all dissociants detected in all systems was their plasmid profile: in phase I, plasmids of 120 and 60 Md, as well as small plasmids, were detected; in phase II disassociants, plasmid with a molecular weight of 120 Md was absent. The restriction analysis of total plasmid DNA by means of restrictase EcoR1 showed the absence of 3 fragments in phase II while other 13 fragments were retained. These results open prospects for the molecular cloning of the gene antigen of phase II.

Topics: Animals; Cell Division; Deoxycholic Acid; DNA, Bacterial; Dysentery, Bacillary; Genetic Variation; Germ-Free Life; Intestines; Plasmids; Rats; Rats, Inbred F344; Shigella sonnei

Topics: Agar; Child; Child, Preschool; Culture Media; Deoxycholic Acid; Diarrhea; Dysentery, Bacillary; Female; Humans; Infant; Infant, Newborn; Male; Shigella; Xylose

Fecal bile acid and neutral sterol patterns of five healthy adult male volunteers, who were challenged by a virulent Shigella flexneri 2a (M42-43) strain and developed dysentery were studied. It was observed that cholic acid was increased from 1.9 +/- 0.4% of total bile acid in the feces before infection to 14.5 +/- 2.1% during diarrhea (P less than 0.001). Chenodeoxycholic acid also was increased from 3.2 +/- 0.7 to 8.7 +/- 3.2% in diarrhea but the difference was not significant statistically. Deoxycholic and lithocholic acids constituted 34.1 +/- 4.1 and 40.5 +/- 2.8%, respectively, of total bile acid in the normal controls as compared to 13.9 +/- 2.5 and 24.8 +/- 2.5% for the same subjects during diarrhea (P less than 0.005). Total excretion of bile acids, expressed as mg/kg of body weight per day, were higher in diarrhea (5.4 +/- 1.0) than that in controls (4,2 +/- 1.0) but the difference was not statistically significant. In the neutral sterol fraction, unmodified cholesterol was increased during diarrhea (86.2 +/- 8.7 versus 25.0 +/- 4.8% of total cholesterol metabolites in controls, P less than 0.001). Coprostanol was decreased in shigellosis (12.2 +/- 8.2 versus 65.8 +/- 4.7% in controls, P less than 0.001). Epicoprostanol, coprostanone, and unidentified cholesterol metabolites also were reduced in shigellosis. The effect of diarrhea on the plant sterols was not as consistent. However, unidentified plant sterols were reduced significantly in shigellosis stools. Total excretion of cholesterol metabolites and plant sterols, when expressed as mg/kg of body weight per day, were 6.8 +/- 1.7 and 0.6 +/- 0.2), respectively, in Shigellosis. These values were not significantly different from the corresponding values for controls (10.3 +/- 3.0 and 0.8 +/- 0.2). One subject's stool samples were studied during infection for the sequence of bile acid alteration. A progressive reduction of bacterial activity upon fecal steroids was evident following the initial diarrheal episode. The production of coprostanol was correlated with 7 alpha-dehydroxylation of cholic acid (r = 0.937, P less than 0.001) and chenodeoxycholic acid (r = 0.755, P less than 0.01).

Topics: Acute Disease; Adult; Bile Acids and Salts; Chenodeoxycholic Acid; Cholesterol; Cholic Acids; Deoxycholic Acid; Dysentery, Bacillary; Feces; Humans; Lithocholic Acid; Male; Phytosterols; Shigella flexneri; Sitosterols; Sterols; Stigmasterol

Topics: Bacillus; Citrates; Citric Acid; Deoxycholic Acid; Dysentery; Dysentery, Bacillary; Humans; Lacticaseibacillus casei

Topics: Bile Acids and Salts; Citrates; Citric Acid; Deoxycholic Acid; Dysentery, Bacillary; Escherichia coli; Salts; Shigella