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ShiA abrogates the innate T-cell response to Shigella flexneri infection.

ABSTRACT: Shigella spp. are the causative agent of bacillary dysentery. Infection results in acute colonic injury due to the host inflammatory response. The mediators of the damage, infiltrating polymorphonuclear leukocytes (PMN), also resolve the infection. Shigella flexneri's virulence effectors are encoded on its large virulence plasmid and on pathogenicity islands in the chromosome. The SHI-2 pathogenicity island encodes the virulence factor ShiA, which down-regulates Shigella-induced inflammation. In the rabbit ileal loop model, infection with a shiA null strain (DeltashiA) induces a more severe inflammation than wild-type infection. Conversely, a Shigella strain that overexpresses ShiA (ShiA+) is less inflammatory than the wild-type strain. To determine the host responses modulated by ShiA, we performed infection studies using the mouse lung model, which recapitulates the phenotypes observed in the rabbit ileal loop model. Significantly, ShiA+ strain-infected mice cleared the bacteria and survived infection, while wild-type- and DeltashiA strain-infected mice could not clear the bacteria and ultimately died. Surprisingly, microarray analysis of infected lungs revealed the regulation of genes involved in innate T-cell responses to infection. Immunohistochemistry showed that wild-type- and DeltashiA strain-infected animals have greater numbers of PMN and T cells in their lungs over the course of infection than ShiA+ strain-infected animals. These results suggest that the T-cell innate response is suppressed by ShiA in Shigella infections.

SUBMITTER: Ingersoll MA

PROVIDER: S-EPMC1418937 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Berberine is a natural isoquinoline alkaloid found in Chinese medicinal herbs which is active against a variety of microbial infections. To examine the potential effects of berberine on Shigella flexneri, a whole-genome DNA microarray was constructed and transcriptome analysis of the cellular responses of S.flexneri when exposed to Berberine Chloride (BC) was performed. When cultures were grown to early exponential growth phase, drug was added. Meanwhile, DMSO solution without BC was added to control cultures to the same final concentration. At 30 min after treatment, samples were collected and washed twice with phosphate buffered saline at 25°C for subsequent RNA isolation. To prepare biological replicates for RNA isolation, each experiment was independently performed three times. After drug treatment, total RNA was extracted using SV RNA Isolation System (Promega). Reverse transcription of 20 ug RNA from each sample was performed with Superscript II system (Invitrogen) to prepare cDNA. According to the manufacturer's instructions, the cDNA was labeled with incorporation of fluorescent dyes (Amersham). Cy3-dCTP monofunctional dye was selected for control cDNA samples and Cy5-dCTP was used for drug-treated samples. Each pair of labeled cDNA was mixed and dried by vacuum centrifugation. The pairs of the labeled cDNA samples were hybridized to the DNA microarrays following the protocol available at http://www.ifr.ac.uk/safety/microarrays/. The slides were scanned by using a GenePix 4100A scanner. Fluorescent spots and local background intensities were quantified using GenePix Pro 6.0 software (Axon). Signal intensities were corrected by subtracting the local background value. The data set was filtered so that spots flagged as "not found," "bad," and "empty" were excluded from further analysis. Moreover, spots either with signal-to-noise ratio below the detection limit of 3 or containing less than 55% of pixels two standard deviations above background in both channels were discarded from the data set. Lowess normalization was performed with the fluorescent signal ratios (Cy5/Cy3) using MIDAS software (http://www.tigr.org/software/tm4) with a 0.33 smooth parameter.

Project description:Shigella flexneri is an intracellular human pathogen that invades colonic cells and causes bloody diarrhea. S. flexneri evolved from commensal Escherichia coli, and genome comparisons reveal that S. flexneri has lost approximately 20% of its genes through the process of pathoadaptation, including a disproportionate number of genes associated with the turnover of the nucleotide-based second messenger cyclic di-GMP (c-di-GMP); however, the remaining c-di-GMP turnover enzymes are highly conserved. c-di-GMP regulates many behavioral changes in other bacteria in response to changing environmental conditions, including biofilm formation, but this signaling system has not been examined in S. flexneri. In this study, we expressed VCA0956, a constitutively active c-di-GMP synthesizing diguanylate cyclase (DGC) from Vibrio cholerae, in S. flexneri to determine if virulence phenotypes were regulated by c-di-GMP. We found that expressing VCA0956 in S. flexneri increased c-di-GMP levels, and this corresponds with increased biofilm formation and reduced acid resistance, host cell invasion, and plaque size. We examined the impact of VCA0956 expression on the S. flexneri transcriptome and found that genes related to acid resistance were repressed, and this corresponded with decreased survival to acid shock. We also found that individual S. flexneri DGC mutants exhibit reduced biofilm formation and reduced host cell invasion and plaque size, as well as increased resistance to acid shock. This study highlights the importance of c-di-GMP signaling in regulating S. flexneri virulence phenotypes. IMPORTANCE The intracellular human pathogen Shigella causes dysentery, resulting in as many as one million deaths per year. Currently, there is no approved vaccine for the prevention of shigellosis, and the incidence of antimicrobial resistance among Shigella species is on the rise. Here, we explored how the widely conserved c-di-GMP bacterial signaling system alters Shigella behaviors associated with pathogenesis. We found that expressing or removing enzymes associated with c-di-GMP synthesis results in changes in Shigella's ability to form biofilms, invade host cells, form lesions in host cell monolayers, and resist acid stress.

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ShiA abrogates the innate T-cell response to Shigella flexneri infection.

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