hfq regulates acid tolerance and virulence by responding to acid stress in Shigella flexneri

Molecular mechanism of Hfq-dependent sRNA1039 and sRNA1600 regulating antibiotic resistance and virulence in Shigella sonnei

Bacillary dysentery caused by Shigella spp. is a significant concern for human health. Small non-coding RNA (sRNA) plays a crucial role in regulating antibiotic resistance and virulence in Shigella spp. However, the specific mechanisms behind this phenomenon are still not fully understood. This study discovered two sRNAs (sRNA1039 and sRNA1600) that may be involved in bacterial resistance and virulence. By constructing deletion mutants (WT/ΔSR1039 and WT/ΔSR1600), this study found that the WT/ΔSR1039 mutants caused a two-fold increase in sensitivity to ampicillin, gentamicin and cefuroxime, and the WT/ΔSR1600 mutants caused a two-fold increase in sensitivity to cefuroxime. Furthermore, the WT/ΔSR1600 mutants caused a decrease in the adhesion and invasion of bacteria to HeLa cells (P<0.01), and changed the oxidative stress level of bacteria to reduce their survival rate (P<0.001). Subsequently, this study explored the molecular mechanisms by which sRNA1039 and sRNA1600 regulate antibiotic resistance and virulence. The deletion of sRNA1039 accelerated the degradation of target gene cfa mRNA and reduced its expression, thereby regulating the expression of pore protein gene ompD indirectly and negatively to increase bacterial sensitivity to ampicillin, gentamicin and cefuroxime. The inactivation of sRNA1600 reduced the formation of persister cells to reduce resistance to cefuroxime, and reduced the expression of type-III-secretion-system-related genes to reduce bacterial virulence by reducing the expression of target gene tomB. These results provide new insights into Hfq-sRNA-mRNA regulation of the resistance and virulence network of Shigella sonnei, which could potentially promote the development of more effective treatment strategies.

Insight into a natural novel histidine decarboxylase gene deletion in Enterobacter hormaechei RH3 from traditional Sichuan-style sausage

Histamine (HIS) is primarily formed from decarboxylated histidine by certain bacteria with histidine decarboxylase (hdc) activity and is the most toxic biogenic amine. Hdc, which is encoded by the hdc gene, serves as a key enzyme that controls HIS production in bacteria. In this paper, we characterized the changes in microbial and biogenic amines content of traditional Sichuan-style sausage before and after storage and demonstrated that Enterobacteriaceae play an important role in the formation of HIS. To screen for Enterobacteriaceae with high levels of HIS production, we isolated strain RH3 which has a HIS production of 2.27 mg/mL from sausages stored at 37°C for 180 days, using selective media and high-performance liquid chromatography. The strain RH3 can produce a high level of HIS after 28 h of fermentation with a significant hysteresis. Analysis of the physicochemical factors revealed that RH3 still retained its ability to partially produce HIS in extreme environments with pH 3.5 and 10.0. In addition, RH3 exhibited excellent salt tolerance (6.0% NaCl and 1.0% NaNO2 ). Subsequently, RH3 was confirmed as Enterobacter hormaechei with hdc gene deletion by PCR, western blot, and whole-genome sequencing analysis. Furthermore, RH3 exhibited pathogenicity rate of 75.60% toward the organism, indicating that it was not a food-grade safe strain, and demonstrated a high level of conservation in intraspecific evolution. The results of this experiment provide a new reference for studying the mechanism of HIS formation in microorganisms. PRACTICAL APPLICATION: This study provides a new direction for investigating the mechanism of histamine (HIS) formation by microorganisms and provides new insights for further controlling HIS levels in meat products. Further research can control the key enzymes that form HIS to control HIS levels in food.

Pathogenicity and virulence of Shigella sonnei: A highly drug-resistant pathogen of increasing prevalence

Shigella spp. are the causative agent of shigellosis (or bacillary dysentery), a diarrhoeal disease characterized for the bacterial invasion of gut epithelial cells. Among the 4 species included in the genus, Shigella flexneri is principally responsible for the disease in the developing world while Shigella sonnei is the main causative agent in high-income countries. Remarkably, as more countries improve their socioeconomic conditions, we observe an increase in the relative prevalence of S. sonnei. To date, the reasons behind this change in aetiology depending on economic growth are not understood. S. flexneri has been widely used as a model to study the pathogenesis of the genus, but as more research data are collected, important discrepancies with S. sonnei have come to light. In comparison to S. flexneri, S. sonnei can be differentiated in numerous aspects; it presents a characteristic O-antigen identical to that of one serogroup of the environmental bacterium Plesiomonas shigelloides, a group 4 capsule, antibacterial mechanisms to outcompete and displace gut commensal bacteria, and a poorer adaptation to an intracellular lifestyle. In addition, the World Health Organization (WHO) have recognized the significant threat posed by antibiotic-resistant strains of S. sonnei, demanding new approaches. This review gathers knowledge on what is known about S. sonnei within the context of other Shigella spp. and aims to open the door for future research on understanding the increasing spread of this pathogen.

Involvement of RNA chaperone Hfq in the regulation of antibiotic resistance and virulence in Shigella sonnei

The host factor for RNA phage Qβ replicase (Hfq) is a crucial post-transcriptional regulator in many bacterial pathogens, facilitating the interaction between small non-coding RNAs (sRNAs) and their target mRNAs. Studies have suggested that Hfq plays a role in antibiotic resistance and virulence in bacteria, although its functions in Shigella are not fully understood. In this study, we investigated the functional roles of Hfq in Shigella sonnei (S. sonnei) by constructing an hfq deletion mutant. Our phenotypic assays showed that the hfq deletion mutant was more sensitivity to antibiotics and had impaired virulence. Transcriptome analyses supported the results concerning the phenotype of the hfq mutant and showed that differentially expressed genes were mainly enriched in the KEGG pathways two-component system, ABC transporters, ribosome, and Escherichia coli biofilm formation. Additionally, we predicted eleven novel Hfq-dependent sRNAs, which were potentially involved in the regulation of antibiotic resistance and/or virulence in S. sonnei. Our findings suggest that Hfq plays a post-transcriptional role in regulating antibiotic resistance and virulence in S. sonnei, and could provide a basis for future studies on Hfq-sRNA-mRNA regulatory networks in this important pathogen.

Disruption of the sensor kinase phoQ gene decreases acid resistance in plant growth-promoting rhizobacterium Rahnella aquatilis HX2

AIMS

Rahnella aquatilis HX2, a promising plant growth-promoting rhizobacterium (PGPR) in the field, contains genes homologous to the PhoP/PhoQ two-component regulatory system. Although this system regulates stress response in numerous pathogens, PhoP/PhoQ characterization in a PGPR has not received in-depth exploration.

METHODS AND RESULTS

The phoQ gene was mutated in strain HX2 using an in-frame deletion strategy. Compared to the wild type, the phoQ mutant exhibited increased sensitivity to acidic conditions (pH 4.0) in a chemically defined medium and in mild acidic natural soil (pH 5.7). The phoQ mutant also exhibited increased swimming motility under acidic conditions. Acid resistance was restored in the mutant by introducing the phoQ gene on a plasmid. Three acid resistance genes, add, cfa, and fur were downregulated significantly, whereas the chaperone encoding gene, dnak, was upregulated when the phoQ mutant was exposed to acid stress.

CONCLUSIONS

This study suggested that the PhoP/PhoQ system positively regulates the acid resistance of R. aquatilis HX2.

Flavonoids and Phenolic Acids from Aerial Part of Ajuga integrifolia (Buch.-Ham. Ex D. Don): Anti-Shigellosis Activity and In Silico Molecular Docking Studies

Shigellosis is one of the major causes of death in children worldwide. Flavonoids and phenolic acids are expected to demonstrate anti-shigellosis activity and anti-diarrheal properties. The aerial part of A. integrifolia is commonly used against diarrhea. This study aimed to identify flavonoids and phenolic acids responsible for this therapeutic purpose. Antioxidant activity, total phenol content, and total flavonoid content were determined. The antibacterial activity of the aerial part against Shigella spp. was also tested using the agar well diffusion method. HPLC analysis was performed using UHPLC-DAD for different extracts of the aerial part. Autodock Vina in the PyRx platform was used to screen responsible components. Ciprofloxacin was used as a reference drug. An enzyme taking part in pyrimidine biosynthesis was used as a target protein. Molecular docking results were visualized using Discovery Studio and LigPlot1.4.5 software. Antioxidant activity, total phenol content, and total flavonoid content are more significant for the aerial part of A. integrifolia. From HPLC analysis, the presence of the flavonoids, quercetin, myricetin, and rutin and the phenolic acids gallic acid, chlorogenic acid, and syringic acid were identified from the aerial part of A. integrifolia. Regarding the antibacterial activity, the aerial part shows considerable activity against Shigella spp. Binding energies, RMSD and Ki values, interaction type, and distance are considered to identify the components most likely responsible for the therapeutic effects and observed activity. Antioxidant activity, total phenol content, and total flavonoid content of the aerial part are in line with anti-shigellosis activity. The top five components that are most likely potentially responsible for therapeutic purposes and anti-shigellosis activity are chlorogenic acid, rutin, dihydroquercetin, dihydromyricetin, and kaempferol.

Bacteroides thetaiotaomicron Outer Membrane Vesicles Modulate Virulence of Shigella flexneri

The role of the gut microbiota in the pathogenesis of Shigella flexneri remains largely unknown. To understand the impact of the gut microbiota on S. flexneri virulence, we examined the effect of interspecies interactions with Bacteroides thetaiotaomicron, a prominent member of the gut microbiota, on S. flexneri invasion. When grown in B. thetaiotaomicron-conditioned medium, S. flexneri showed reduced invasion of human epithelial cells. This decrease in invasiveness of S. flexneri resulted from a reduction in the level of the S. flexneri master virulence regulator VirF. Reduction of VirF corresponded with a decrease in expression of a secondary virulence regulator, virB, as well as expression of S. flexneri virulence genes required for invasion, intracellular motility, and spread. Repression of S. flexneri virulence factors by B. thetaiotaomicron-conditioned medium was not caused by either a secreted metabolite or secreted protein but rather was due to the presence of B. thetaiotaomicron outer membrane vesicles (OMVs) in the conditioned medium. The addition of purified B. thetaiotaomicron OMVs to S. flexneri growth medium recapitulated the inhibitory effects of B. thetaiotaomicron-conditioned medium on invasion, virulence gene expression, and virulence protein levels. Total lipids extracted from either B. thetaiotaomicron cells or B. thetaiotaomicron OMVs also recapitulated the effects of B. thetaiotaomicron-conditioned medium on expression of the S. flexneri virulence factor IpaC, indicating that B. thetaiotaomicron OMV lipids, rather than a cargo contained in the vesicles, are the active factor responsible for the inhibition of S. flexneri virulence. IMPORTANCE Shigella flexneri is the causative agent of bacillary dysentery in humans. Shigella spp. are one of the leading causes of diarrheal morbidity and mortality, especially among children in low- and middle-income countries. The rise of antimicrobial resistance combined with the lack of an effective vaccine for Shigella heightens the importance of studies aimed at better understanding previously uncharacterized aspects of Shigella pathogenesis. Here, we show that conditioned growth medium from the commensal bacterium Bacteroides thetaiotaomicron represses the invasion of S. flexneri. This repression is due to the presence of B. thetaiotaomicron outer membrane vesicles. These findings establish a role for interspecies interactions with a prominent member of the gut microbiota in modulating the virulence of S. flexneri and identify a novel function of outer membrane vesicles in interbacterial signaling between members of the gut microbiota and an enteric pathogen.

Relative expression and validation of Aeromonas salmonicida subsp. salmonicida reference genes during ex vivo and in vivo fish infection

The genus Aeromonas is found worldwide in freshwater and marine environments and has been implicated in the etiology of human and animal diseases. In fish, among Aeromonas species, A. salmonicida causes massive mortality and great economic losses in marine and continental aquaculture species. Currently, several aspects of the clinical signs and pathogenesis of this Gram-negative bacterium have been described; however, determination of an appropriate reference gene is essential to normalize cellular mRNA data remain unknown. Here we evaluate the stability of seven candidate reference genes to be used for data normalization during ex vivo and in vivo experiments conducted in Atlantic cod, Atlantic salmon, and lumpfish. To assess this, raw Ct values obtained were evaluated by using geNorm, NormFinder, BestKeeper, Delta Ct comparison, and the comprehensive ranking, through the bioinformatic open-access portal RefFinder. We determined that fabD and era were most suitable reference genes in Atlantic cod primary macrophages, hfq and era in Atlantic salmon primary macrophages, rpoB and fabD in lumpfish head kidney samples, and hfq and era in lumpfish spleen. Our study demonstrates that use of multiple reference genes and its validation before measurements helps to minimize variability arising in qPCR studies that evaluate A. salmonicida gene expression in fish tissues. Overall, this study provided with an expanded list of reliable reference genes for A. salmonicida gene expression using qPCR during fish infection studies.

Effect of 405-nm light-emitting diode on environmental tolerance of Cronobacter sakazakii in powdered infant formula

Cronobacter sakazakii is an opportunistic pathogen that can survive extreme desiccation, heat, acid, and osmotic stress. This can increase the risk of infection, resulting in severe diseases, mainly in neonates. The inactivation effect of 405 ± 5-nm light-emitting diode (LED) illumination on C. sakazakii with different initial concentrations and C. sakazakii strains isolated from powdered infant formula (PIF) and baby rice cereal (BRC) were firstly evaluated. Then, the effect of 405 ± 5-nm LED on the tolerance of diverse environmental conditions of C. sakazakii in PIF was investigated. Conditions involving desiccation [PIF, Water activity (a_w): 0.2-0.5], heat (45, 50, and 55 °C), acid (simulated gastric fluid: SGF, pH 4.75 ± 0.25), and bile salt (0.2%, bile salt solution) were used to study the effects of 405-nm LED on C. sakazakii resistance. The transcription levels of ten tolerance-associated genes and changes in bacterial cell membrane were examined to understand the response of C. sakazakii to LED illumination. The results showed that 405-nm LED effectively inactivated C. sakazakii ATCC 29544 with initial concentration from 8 to 1 log CFU/g in PIF and strains isolated from PIF and BRC. Moreover, 405-nm LED could decrease the tolerance of C. sakazakii in PIF to desiccation, heat treatment at 50 and 55 °C, SGF, and bile salt to different degrees, but the resistance to the heat treatment at 45 °C was not influenced by LED illumination. In addition, the transcription levels of the ten tolerance-associated genes measured in the LED-illuminated C. sakazakii cells were significantly downregulated compared with those in unilluminated controls. The damage on cell membrane was confirmed for LED-treated cells by LIVE/DEAD® assay. These results indicate that 405-nm LED illumination may be effective at reducing the environmental resistance of C. sakazakii in PIF. Furthermore, this study suggests the potential for applying 405-nm LED technology in the prevention and control of pathogens in food processing, production, and storage environments.

Expression of stress regulator and virulence genes of Cronobacter sakazakii strain Yrt2a as a response to acid stress

This research aimed to evaluate the effect of acid stress on the expression of stress regulator (grxB and rpoS) and virulence (ompA, hfq, and cpa) genes of Cronobacter sakazakii Yrt2a. The results showed that C. sakazakii Yrt2a experienced decrease in number during acid stress and was no longer culturable 90 min post exposure to pH 3.0. During acid stress, the expression of grxB, rpoS, ompA, cpa and hfq was upregulated by 2.15; 2.19; 1.55; 1.1 and 1.41 log, respectively. However, all genes expression was downregulated when the bacteria entered the unculturable state. The expression of gene grxB, rpoS, ompA, cpa decreased to 1.04; 0.37; 0.84 and 1.71 log, respectively; while hfq gene expression reached a level lower than that of control. This research implies a supposition that during acid stress, C. sakazakii was capable of maintaining its culturability and pathogenicity until they are no longer culturable.

The RNase YbeY Is Vital for Ribosome Maturation, Stress Resistance, and Virulence of the Natural Genetic Engineer Agrobacterium tumefaciens

Riboregulation involving regulatory RNAs, RNA chaperones, and ribonucleases is fundamental for the rapid adaptation of gene expression to changing environmental conditions. The gene coding for the RNase YbeY belongs to the minimal prokaryotic genome set and has a profound impact on physiology in a wide range of bacteria. Here, we show that the Agrobacterium tumefaciens ybeY gene is not essential. Deletion of the gene in the plant pathogen reduced growth, motility, and stress tolerance. Most interestingly, YbeY is crucial for A. tumefaciens-mediated T-DNA transfer and tumor formation. Comparative proteomics by using isobaric tags for relative and absolute quantitation (iTRAQ) revealed dysregulation of 59 proteins, many of which have previously been found to be dependent on the RNA chaperone Hfq. YbeY and Hfq have opposing effects on production of these proteins. Accumulation of a 16S rRNA precursor in the ybeY mutant suggests that A. tumefaciens YbeY is involved in rRNA processing. RNA coimmunoprecipitation-sequencing (RIP-Seq) showed binding of YbeY to the region immediately upstream of the 16S rRNA. Purified YbeY is an oligomer with RNase activity. It does not physically interact with Hfq and thus plays a partially overlapping but distinct role in the riboregulatory network of the plant pathogen.IMPORTANCE Although ybeY gene belongs to the universal bacterial core genome, its biological function is incompletely understood. Here, we show that YbeY is critical for fitness and host-microbe interaction in the plant pathogen Agrobacterium tumefaciens Consistent with the reported endoribonuclease activity of YbeY, A. tumefaciens YbeY acts as a RNase involved in maturation of 16S rRNA. This report adds a worldwide plant pathogen and natural genetic engineer of plants to the growing list of bacteria that require the conserved YbeY protein for host-microbe interaction.

Shigella Pathogenesis: New Insights through Advanced Methodologies

Shigella is a genus of Gram-negative enteropathogens that have long been, and continue to be, an important public health concern worldwide. Over the past several decades, Shigella spp. have also served as model pathogens in the study of bacterial pathogenesis, and Shigella flexneri has become one of the best-studied pathogens on a molecular, cellular, and tissue level. In the arms race between Shigella and the host immune system, Shigella has developed highly sophisticated mechanisms to subvert host cell processes in order to promote infection, escape immune detection, and prevent bacterial clearance. Here, we give an overview of Shigella pathogenesis while highlighting innovative techniques and methods whose application has significantly advanced our understanding of Shigella pathogenesis in recent years.

Enteropathogens: Tuning Their Gene Expression for Hassle-Free Survival

Enteropathogenic bacteria have been the cause of the majority of foodborne illnesses. Much of the research has been focused on elucidating the mechanisms by which these pathogens evade the host immune system. One of the ways in which they achieve the successful establishment of a niche in the gut microenvironment and survive is by a chain of elegantly regulated gene expression patterns. Studies have shown that this process is very elaborate and is also regulated by several factors. Pathogens like, enteropathogenic Escherichia coli (EPEC), Salmonella Typhimurium, Shigellaflexneri, Yersinia sp. have been seen to employ various regulated gene expression strategies. These include toxin-antitoxin systems, quorum sensing systems, expression controlled by nucleoid-associated proteins (NAPs), several regulons and operons specific to these pathogens. In the following review, we have tried to discuss the common gene regulatory systems of enteropathogenic bacteria as well as pathogen-specific regulatory mechanisms.

An H-NS Family Protein, Sfh, Regulates Acid Resistance by Inhibition of Glutamate Decarboxylase Expression in Shigella flexneri 2457T

The glutamate-dependent acid-resistance system is the most effective acid tolerance pathway in Shigella, allowing survival in extremely acidic environments. However, the regulation of this system in Shigella remains elusive. In the current study, we identified significant differences in the levels of glutamate decarboxylase between three Shigella flexneri strains with different levels of acid resistance using blue native-polyacrylamide gel electrophoresis (PAGE) and isoelectric focusing (IEF)/sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis. The results showed that the degree of acid resistance and the levels of GadA/B were significantly lower in strain 2457T compared with two other S. flexneri strains. It has been reported that plasmid pSf-R27 is expressed in strain 2457T but not in the other 142 sequenced S. flexneri isolates. pSf-R27 encodes protein Sfh, which belongs to a family of histone-like nucleoid-structuring (H-NS) proteins that participate in the transcriptional control of glutamate-dependent acid resistance, implicating pSf-R27 in the lower acid resistance of strain 2457T. Transformation of pSf-R27 or sfh alone into strain 301 resulted in decreased expression of GadA/B in the recombinant strains. Thus, we confirmed that H-NS family protein Sfh, bound to the gadA/B regulatory region and regulates the expression of glutamate decarboxylase at the transcriptional level. We also examined the acid tolerance of the wild-type and recombinant strains using flow cytometry and determined that the acid tolerance of S. flexneri is closely related to the expression of GadA/B. These findings further our understanding of the acid tolerance of S. flexneri, especially via the glutamate-dependent pathway.

Global Screening of Salmonella enterica Serovar Typhimurium Genes for Desiccation Survival

Salmonella spp., one of the most common foodborne bacterial pathogens, has the ability to survive under desiccation conditions in foods and food processing facilities for years. This raises the concerns of Salmonella infection in humans associated with low water activity foods. Salmonella responds to desiccation stress via complex pathways involving immediate physiological actions as well as coordinated genetic responses. However, the exact mechanisms of Salmonella to resist desiccation stress remain to be fully elucidated. In this study, we screened a genome-saturating transposon (Tn5) library of Salmonella Typhimurium (S. Typhimurium) 14028s under the in vitro desiccation stress using transposon sequencing (Tn-seq). We identified 61 genes and 6 intergenic regions required to overcome desiccation stress. Salmonella desiccation resistance genes were mostly related to energy production and conversion; cell wall/membrane/envelope biogenesis; inorganic ion transport and metabolism; regulation of biological process; DNA metabolic process; ABC transporters; and two component system. More than 20% of the Salmonella desiccation resistance genes encode either putative or hypothetical proteins. Phenotypic evaluation of 12 single gene knockout mutants showed 3 mutants (atpH, atpG, and corA) had significantly (p < 0.02) reduced survival as compared to the wild type during desiccation survival. Thus, our study provided new insights into the molecular mechanisms utilized by Salmonella for survival against desiccation stress. The findings might be further exploited to develop effective control strategies against Salmonella contamination in low water activity foods and food processing facilities.

Role of the virulence plasmid in acid resistance of Shigella flexneri

Virulence plasmid (VP) acquisition was a key step in the evolution of Shigella from a non-pathogenic Escherichia coli ancestor to a pathogenic genus. In addition, the co-evolution and co-ordination of chromosomes and VPs was also a very important step in the evolutionary process. To investigate the cross-talk between VPs and bacterial chromosomes, we analyzed the expression profiles of protein complexes and protein monomers in three wild-type Shigella flexneri strains and their corresponding VP deletion mutants. A non-pathogenic wild-type E. coli strain and mutant E. coli strains harboring three Shigella VPs were also analyzed. Comparisons showed that the expression of chromosome-encoded proteins GadA/B and AtpA/D, which are associated with intracellular proton flow and pH tuning of bacterial cells, was significantly altered following acquisition or deletion of the VP. The acid tolerance of the above strains was also compared, and the results confirmed that the presence of the VP reduced the bacterial survival rate in extremely acidic environments, such as that in the host stomach. These results further our understanding of the evolution from non-pathogenic E. coli to Shigella, and highlight the importance of co-ordination between heterologous genes and the host chromosome in the evolution of bacterial species.

Post-transcriptional regulation of type III secretion in plant and animal pathogens

Type III secretion systems (T3SS) serve as a primary anti-host defense mechanism for many Gram-negative plant and animal pathogens. T3SS production is tightly controlled and activated by host-associated signals. Although transcriptional responses represent a significant component of the activation cascade, recent studies have uncovered diverse post-transcriptional mechanisms that also contribute to T3SS production. Targets for post-transcriptional control are often AraC/XylS transcription factors that promote T3SS gene expression. Commons mechanisms of post-transcriptional regulation include direct control of either the activity of AraC/XylS transcription factors by protein ligands, small molecules, or post-translational modification, or transcription factor synthesis. In the latter case, RNA-binding proteins such as Hfq, CsrA/RsmA, and components of the RNA degradosome alter mRNA stability and/or the rate of translation initiation to control transcription factor synthesis. Here we summarize post-transcriptional mechanisms that contribute to the exquisite regulation of T3SS gene expression.

The Orchestra and Its Maestro: Shigella's Fine-Tuning of the Inflammasome Platforms

Shigella spp. are the causative agents of bacillary dysentery, leading to extensive mortality and morbidity worldwide. These facultative intracellular bacteria invade the epithelium of the colon and the rectum, inducing a severe inflammatory response from which the symptoms of the disease originate. Shigella are human pathogens able to manipulate and subvert the innate immune system surveillance. Shigella dampens inflammasome activation in epithelial cells. In infected macrophages, inflammasome activation and IL-1β and IL-18 release lead to massive neutrophil recruitment and greatly contribute to inflammation. Here, we describe how Shigella hijacks and finely tunes inflammasome activation in the different cell populations involved in pathogenesis: epithelial cells, macrophages, neutrophils, DCs, and B and T lymphocytes. Shigella emerges as a "sly" pathogen that switches on/off the inflammasome mechanisms in order to optimize the interaction with the host and establish a successful infection.