scholarly journals Functional Analysis of Lactobacillus rhamnosus GG Pili in Relation to Adhesion and Immunomodulatory Interactions with Intestinal Epithelial Cells

2011 ◽  
Vol 78 (1) ◽  
pp. 185-193 ◽  
Author(s):  
Sarah Lebeer ◽  
Ingmar Claes ◽  
Hanne L. P. Tytgat ◽  
Tine L. A. Verhoeven ◽  
Eyra Marien ◽  
...  
Keyword(s):  
Lactobacillus Rhamnosus ◽  
Lipoteichoic Acid ◽  
Good Survival ◽  
Intestinal Epithelial ◽  
Wild Type ◽  
Knockout Mutant ◽  
Phenotypic Analysis ◽  
Adhesion Properties ◽  
Content Type ◽  
Adhesive Interactions

ABSTRACTLactobacillus rhamnosusGG, a probiotic with good survival capacity in the human gut, has well-documented adhesion properties and health effects. Recently,spaCBA-encoded pili that bind to human intestinal mucus were identified on its cell surface. Here, we report on the phenotypic analysis of aspaCBApilus knockout mutant in comparison with the wild type and other adhesin mutants. The SpaCBA pilus ofL. rhamnosusGG showed to be key for efficient adherence to the Caco-2 intestinal epithelial cell (IEC) line and biofilm formation. Moreover, thespaCBAmutant induces an elevated level of interleukin-8 (IL-8) mRNA in Caco-2 cells compared to the wild type, possibly involving an interaction of lipoteichoic acid with Toll-like receptor 2. In contrast, anL. rhamnosusGG mutant without exopolysaccharides but with an increased exposure of pili leads to the reduced expression of IL-8. Using Transwells to partition bacteria from Caco-2 cells, IL-8 induction is blocked completely regardless of whether wild-type or mutantL. rhamnosusGG cells are used. Taken together, our data suggest thatL. rhamnosusGG SpaCBA pili, while promoting strong adhesive interactions with IECs, have a functional role in balancing IL-8 mRNA expression induced by surface molecules such as lipoteichoic acid.

scholarly journals Comparative Genomic and Functional Analysis of Lactobacillus casei and Lactobacillus rhamnosus Strains Marketed as Probiotics

2013 ◽  
Vol 79 (6) ◽  
pp. 1923-1933 ◽  
Author(s):  
François P. Douillard ◽  
Angela Ribbera ◽  
Hanna M. Järvinen ◽  
Ravi Kant ◽  
Taija E. Pietilä ◽  
...  
Keyword(s):  
Gene Cluster ◽  
Transcription Initiation ◽  
Lactobacillus Rhamnosus ◽  
Comparative Genomic ◽  
Phenotypic Analysis ◽  
Carbohydrate Utilization ◽  
Content Type ◽  
Host Signaling ◽  
Toll Like Receptor 2 ◽  
Genome Content

ABSTRACTFourLactobacillusstrains were isolated from marketed probiotic products, includingL. rhamnosusstrains from Vifit (Friesland Campina) and Idoform (Ferrosan) andL. caseistrains from Actimel (Danone) and Yakult (Yakult Honsa Co.). Their genomes and phenotypes were characterized and compared in detail withL. caseistrain BL23 andL. rhamnosusstrain GG. Phenotypic analysis of the new isolates indicated differences in carbohydrate utilization betweenL. caseiandL. rhamnosusstrains, which could be linked to their genotypes. The two isolatedL. rhamnosusstrains had genomes that were virtually identical to that ofL. rhamnosusGG, testifying to their genomic stability and integrity in food products. TheL. caseistrains showed much greater genomic heterogeneity. Remarkably, all strains contained an intactspaCBApilus gene cluster. However, only theL. rhamnosusstrains produced mucus-binding SpaCBA pili under the conditions tested. Transcription initiation mapping demonstrated that the insertion of aniso-IS30element upstream of the pilus gene cluster inL. rhamnosusstrains but absent inL. caseistrains had constituted a functional promoter driving pilus gene expression. AllL. rhamnosusstrains triggered an NF-κB response via Toll-like receptor 2 (TLR2) in a reporter cell line, whereas theL. caseistrains did not or did so to a much lesser extent. This study demonstrates that the twoL. rhamnosusstrains isolated from probiotic products are virtually identical toL. rhamnosusGG and further highlights the differences between these andL. caseistrains widely marketed as probiotics, in terms of genome content, mucus-binding and metabolic capacities, and host signaling capabilities.

scholarly journals Impact of Environmental and Genetic Factors on Biofilm Formation by the Probiotic Strain Lactobacillus rhamnosus GG

2007 ◽  
Vol 73 (21) ◽  
pp. 6768-6775 ◽  
Author(s):  
Sarah Lebeer ◽  
Tine L. A. Verhoeven ◽  
M�nica Perea V�lez ◽  
Jos Vanderleyden ◽  
Sigrid C. J. De Keersmaecker
Keyword(s):  
Biofilm Formation ◽  
Culture Medium ◽  
Lactobacillus Rhamnosus ◽  
Probiotic Strain ◽  
Lipoteichoic Acid ◽  
Microtiter Plate ◽  
Phenotypic Analysis ◽  
Lactobacillus Rhamnosus Gg ◽  
Abiotic Surfaces

ABSTRACTLactobacillus rhamnosusGG (ATCC 53103) is one of the clinically best-studied probiotic organisms. Moreover,L. rhamnosusGG displays very good in vitro adherence to epithelial cells and mucus. Here, we report thatL. rhamnosusGG is able to form biofilms on abiotic surfaces, in contrast to other strains of theLactobacillus caseigroup tested under the same conditions. Microtiter plate biofilm assays indicated that in vitro biofilm formation byL. rhamnosusGG is strongly modulated by culture medium factors and conditions related to the gastrointestinal environment, including low pH; high osmolarity; and the presence of bile, mucins, and nondigestible polysaccharides. Additionally, phenotypic analysis of mutants affected in exopolysaccharides (wzb), lipoteichoic acid (dltD), and central metabolism (luxS) showed their relative importance in biofilm formation byL. rhamnosusGG.

scholarly journals Novel Role for the Streptococcus pneumoniae Toxin Pneumolysin in the Assembly of Biofilms

mBio ◽  
2013 ◽  
Vol 4 (5) ◽  
Author(s):  
Joshua R. Shak ◽  
Herbert P. Ludewick ◽  
Kristen E. Howery ◽  
Fuminori Sakai ◽  
Hong Yi ◽  
...  
Keyword(s):  
Streptococcus Pneumoniae ◽  
Hemolytic Activity ◽  
Biofilm Formation ◽  
Early Time ◽  
Wild Type ◽  
Knockout Mutant ◽  
Content Type ◽  
Biofilm Development ◽  
Almost All

ABSTRACTStreptococcus pneumoniaeis an important commensal and pathogen responsible for almost a million deaths annually in children under five. The formation of biofilms byS. pneumoniaeis important in nasopharyngeal colonization, pneumonia, and otitis media. Pneumolysin (Ply) is a toxin that contributes significantly to the virulence ofS. pneumoniaeand is an important candidate as a serotype-independent vaccine target. Having previously demonstrated that aluxSknockout mutant was unable to form early biofilms and expressed lessplymRNA than the wild type, we conducted a study to investigate the role of Ply in biofilm formation. We found that Ply was expressed in early phases of biofilm development and localized to cellular aggregates as early as 4 h postinoculation.S. pneumoniae plyknockout mutants in D39 and TIGR4 backgrounds produced significantly less biofilm biomass than wild-type strains at early time points, both on polystyrene and on human respiratory epithelial cells, cultured under static or continuous-flow conditions. Ply’s role in biofilm formation appears to be independent of its hemolytic activity, asS. pneumoniaeserotype 1 strains, which produce a nonhemolytic variant of Ply, were still able to form biofilms. Transmission electron microscopy of biofilms grown on A549 lung cells using immunogold demonstrated that Ply was located both on the surfaces of pneumococcal cells and in the extracellular biofilm matrix. Altogether, our studies demonstrate a novel role for pneumolysin in the assembly ofS. pneumoniaebiofilms that is likely important during both carriage and disease and therefore significant for pneumolysin-targeting vaccines under development.IMPORTANCEThe bacteriumStreptococcus pneumoniae(commonly known as the pneumococcus) is commonly carried in the human nasopharynx and can spread to other body sites to cause disease. In the nasopharynx, middle ear, and lungs, the pneumococcus forms multicellular surface-associated structures called biofilms. Pneumolysin is an important toxin produced by almost allS. pneumoniaestrains, extensively studied for its ability to cause damage to human tissue. In this paper, we demonstrate that pneumolysin has a previously unrecognized role in biofilm formation by showing that strains without pneumolysin are unable to form the same amount of biofilm on plastic and human cell substrates. Furthermore, we show that the role of pneumolysin in biofilm formation is separate from the hemolytic activity responsible for tissue damage during pneumococcal diseases. This novel role for pneumolysin suggests that pneumococcal vaccines directed against this protein should be investigated for their potential impact on biofilms formed during carriage and disease.

scholarly journals A Novel Sterol Desaturase-Like Protein Promoting Dealkylation of Phytosterols in Tetrahymena thermophila

2011 ◽  
Vol 10 (3) ◽  
pp. 423-434 ◽  
Author(s):  
Mariela L. Tomazic ◽  
Sebastián R. Najle ◽  
Alejandro D. Nusblat ◽  
Antonio D. Uttaro ◽  
Clara B. Nudel
Keyword(s):  
Wild Type Strain ◽  
Tetrahymena Thermophila ◽  
Wild Type ◽  
Knockout Mutant ◽  
Transfer Event ◽  
Content Type ◽  
Ethyl Group ◽  
Fatty Acid Hydroxylase ◽  
Eukaryotic Proteins ◽  
The One

ABSTRACT The gene TTHERM_00438800 ( DES24 ) from the ciliate Tetrahymena thermophila encodes a protein with three conserved histidine clusters, typical of the fatty acid hydroxylase superfamily. Despite its high similarity to sterol desaturase-like enzymes, the phylogenetic analysis groups Des24p in a separate cluster more related to bacterial than to eukaryotic proteins, suggesting a possible horizontal gene transfer event. A somatic knockout of DES24 revealed that the gene encodes a protein, Des24p, which is involved in the dealkylation of phytosterols. Knocked-out mutants were unable to eliminate the C-24 ethyl group from C 29 sterols, whereas the ability to introduce other modifications, such as desaturations at positions C-5(6), C-7(8), and C-22(23), were not altered. Although C-24 dealkylations have been described in other organisms, such as insects, neither the enzymes nor the corresponding genes have been identified to date. Therefore, this is the first identification of a gene involved in sterol dealkylation. Moreover, the knockout mutant and wild-type strain differed significantly in growth and morphology only when cultivated with C 29 sterols; under this culture condition, a change from the typical pear-like shape to a round shape and an alteration in the regulation of tetrahymanol biosynthesis were observed. Sterol analysis upon culture with various substrates and inhibitors indicate that the removal of the C-24 ethyl group in Tetrahymena may proceed by a mechanism different from the one currently known.

scholarly journals Experimental Evolution of a Facultative Thermophile from a Mesophilic Ancestor

2011 ◽  
Vol 78 (1) ◽  
pp. 144-155 ◽  
Author(s):  
Ian K. Blaby ◽  
Benjamin J. Lyons ◽  
Ewa Wroclawska-Hughes ◽  
Grier C. F. Phillips ◽  
Tyler P. Pyle ◽  
...  
Keyword(s):  
Experimental Evolution ◽  
Complex Traits ◽  
Membrane Lipids ◽  
Thermal Adaptation ◽  
Environmental Parameters ◽  
Genetic Alterations ◽  
Degree Of Saturation ◽  
Wild Type ◽  
Phenotypic Analysis ◽  
Content Type

ABSTRACTExperimental evolution via continuous culture is a powerful approach to the alteration of complex phenotypes, such as optimal/maximal growth temperatures. The benefit of this approach is that phenotypic selection is tied to growth rate, allowing the production of optimized strains. Herein, we demonstrate the use of a recently described long-term culture apparatus called the Evolugator for the generation of a thermophilic descendant from a mesophilic ancestor (Escherichia coliMG1655). In addition, we used whole-genome sequencing of sequentially isolated strains throughout the thermal adaptation process to characterize the evolutionary history of the resultant genotype, identifying 31 genetic alterations that may contribute to thermotolerance, although some of these mutations may be adaptive for off-target environmental parameters, such as rich medium. We undertook preliminary phenotypic analysis of mutations identified in theglpFandfabAgenes. Deletion ofglpFin a mesophilic wild-type background conferred significantly improved growth rates in the 43-to-48°C temperature range and altered optimal growth temperature from 37°C to 43°C. In addition, transforming our evolved thermotolerant strain (EVG1064) with a wild-type allele ofglpFreduced fitness at high temperatures. On the other hand, the mutation infabApredictably increased the degree of saturation in membrane lipids, which is a known adaptation to elevated temperature. However, transforming EVG1064 with a wild-typefabAallele had only modest effects on fitness at intermediate temperatures. The Evolugator is fully automated and demonstrates the potential to accelerate the selection for complex traits by experimental evolution and significantly decrease development time for new industrial strains.

scholarly journals Influence of Adhesion and Bacteriocin Production by Lactobacillus salivarius on the Intestinal Epithelial Cell Transcriptional Response

2012 ◽  
Vol 78 (15) ◽  
pp. 5196-5203 ◽  
Author(s):  
John O'Callaghan ◽  
Ludovica F. Buttó ◽  
John MacSharry ◽  
Kenneth Nally ◽  
Paul W. O'Toole
Keyword(s):  
Epithelial Cell ◽  
Epithelial Cells ◽  
Intestinal Epithelial Cell ◽  
Bacterial Genome ◽  
Intestinal Cell ◽  
Intestinal Epithelial ◽  
Wild Type ◽  
Lactobacillus Salivarius ◽  
Content Type ◽  
Mucin Production

ABSTRACTLactobacillus salivariusstrain UCC118 is a human intestinal isolate that has been extensively studied for its potential probiotic effects in human and animal models. The objective of this study was to determine the effect ofL. salivariusUCC118 on gene expression responses in the Caco-2 cell line to improve understanding of how the strain might modulate intestinal epithelial cell phenotypes. Exposure of Caco-2 cells to UCC118 led to the induction of several human genes (TNFAIP3,NFKBIA, andBIRC3) that are negative regulators of inflammatory signaling pathways. Induction of chemokines (CCL20, CXCL-1, and CXCL-2) with antimicrobial functions was also observed. Disruption of the UCC118 sortase genesrtAcauses reduced bacterial adhesion to epithelial cells. Transcription of three mucin genes was reduced significantly when Caco-2 cells were stimulated with the ΔsrtA derivative of UCC118 compared to cells stimulated with the wild type, but there was no significant change in the transcription levels of the anti-inflammatory genes. UCC118 genes that were significantly upregulated upon exposure to Caco-2 cells were identified by bacterial genome microarray and consisted primarily of two groups of genes connected with purine metabolism and the operon for synthesis of the Abp118 bacteriocin. Following incubation with Caco-2 cells, the bacteriocin synthesis genes were transcribed at higher levels in the wild type than in the ΔsrtAderivative. These data indicate thatL. salivariusUCC118 influences epithelial cells both through modulation of the inflammatory response and by modulation of intestinal cell mucin production. Sortase-anchored cell surface proteins ofL. salivariusUCC118 have a central role in promoting the interaction between the bacterium and epithelial cells.

scholarly journals Broad-Spectrum Regulation of Nonreceptor Tyrosine Kinases by the Bacterial ADP-Ribosyltransferase EspJ

mBio ◽  
2018 ◽  
Vol 9 (2) ◽  
Author(s):  
Dominic J. Pollard ◽  
Cedric N. Berger ◽  
Ernest C. So ◽  
Lu Yu ◽  
Kate Hadavizadeh ◽  
...  
Keyword(s):  
Immune Responses ◽  
Type Iii Secretion ◽  
Tyrosine Kinases ◽  
Intestinal Epithelial ◽  
Wild Type ◽  
Content Type ◽  
Bacterial Effectors ◽  
Adp Ribosyltransferase ◽  
Nonreceptor Tyrosine Kinases

ABSTRACT Tyrosine phosphorylation is key for signal transduction from exogenous stimuli, including the defense against pathogens. Conversely, pathogens can subvert protein phosphorylation to control host immune responses and facilitate invasion and dissemination. The bacterial effectors EspJ and SeoC are injected into host cells through a type III secretion system by enteropathogenic and enterohemorrhagic Escherichia coli (EPEC and EHEC, respectively), Citrobacter rodentium , and Salmonella enterica , where they inhibit Src kinase by coupled amidation and ADP-ribosylation. C. rodentium , which is used to model EPEC and EHEC infections in humans, is a mouse pathogen triggering colonic crypt hyperplasia (CCH) and colitis. Enumeration of bacterial shedding and CCH confirmed that EspJ affects neither tolerance nor resistance to infection. However, comparison of the proteomes of intestinal epithelial cells isolated from mice infected with wild-type C. rodentium or C. rodentium encoding catalytically inactive EspJ revealed that EspJ-induced ADP-ribosylation regulates multiple nonreceptor tyrosine kinases in vivo . Investigation of the substrate repertoire of EspJ revealed that in HeLa and A549 cells, Src and Csk were significantly targeted; in polarized Caco2 cells, EspJ targeted Src and Csk and the Src family kinase (SFK) Yes1, while in differentiated Thp1 cells, EspJ modified Csk, the SFKs Hck and Lyn, the Tec family kinases Tec and Btk, and the adapter tyrosine kinase Syk. Furthermore, Abl (HeLa and Caco2) and Lyn (Caco2) were enriched specifically in the EspJ-containing samples. Biochemical assays revealed that EspJ, the only bacterial ADP-ribosyltransferase that targets mammalian kinases, controls immune responses and the Src/Csk signaling axis. IMPORTANCE Enteropathogenic and enterohemorrhagic Escherichia coli (EPEC and EHEC, respectively) strains cause significant mortality and morbidity worldwide. Citrobacter rodentium is a mouse pathogen used to model EPEC and EHEC pathogenesis in vivo . Diarrheal disease is triggered following injection of bacterial effectors, via a type III secretion system (T3SS), into intestinal epithelial cells (IECs). While insights into the role of the effectors were historically obtained from pathological, immunologic, or cell culture phenotypes, subtle roles of individual effectors in vivo are often masked. The aim of this study was to elucidate the role and specificity of the ADP-ribosyltransferase effector EspJ. For the first time, we show that the in vivo processes affected by a T3SS effector can be studied by comparing the proteomes of IECs extracted from mice infected with wild-type C. rodentium or an espJ catalytic mutant. We show that EspJ, the only bacterial ADP-ribosyltransferase that targets mammalian kinases, regulates the host immune response in vivo .

scholarly journals Synthesis of Short-Chain Diols and Unsaturated Alcohols from Secondary Alcohol Substrates by the Rieske Nonheme Mononuclear Iron Oxygenase MdpJ

2012 ◽  
Vol 78 (17) ◽  
pp. 6280-6284 ◽  
Author(s):  
Franziska Schäfer ◽  
Judith Schuster ◽  
Birgit Würz ◽  
Claus Härtig ◽  
Hauke Harms ◽  
...  
Keyword(s):  
Secondary Alcohol ◽  
Enantiomeric Excess ◽  
Short Chain ◽  
Wild Type ◽  
Knockout Mutant ◽  
Biotechnological Potential ◽  
Content Type ◽  
Mononuclear Iron ◽  
Tertiary Alcohols ◽  
Fuel Oxygenate

ABSTRACTThe Rieske nonheme mononuclear iron oxygenase MdpJ of the fuel oxygenate-degrading bacterial strainAquincola tertiaricarbonisL108 has been described to attack short-chain tertiary alcohols via hydroxylation and desaturation reactions. Here, we demonstrate that also short-chain secondary alcohols can be transformed by MdpJ. Wild-type cells of strain L108 converted 2-propanol and 2-butanol to 1,2-propanediol and 3-buten-2-ol, respectively, whereas anmdpJknockout mutant did not show such activity. In addition, wild-type cells converted 3-methyl-2-butanol and 3-pentanol to the corresponding desaturation products 3-methyl-3-buten-2-ol and 1-penten-3-ol, respectively. The enzymatic hydroxylation of 2-propanol resulted in an enantiomeric excess of about 70% for the (R)-enantiomer, indicating that this reaction was favored. Likewise, desaturation of (R)-2-butanol to 3-buten-2-ol was about 2.3-fold faster than conversion of the (S)-enantiomer. The biotechnological potential of MdpJ for the synthesis of enantiopure short-chain alcohols and diols as building block chemicals is discussed.

scholarly journals Virulence Traits of a Serogroup C Meningococcus and IsogeniccssAMutant, Defective in Surface-Exposed Sialic Acid, in a Murine Model of Meningitis

2019 ◽  
Vol 87 (4) ◽  
Author(s):  
Roberta Colicchio ◽  
Chiara Pagliuca ◽  
Susanna Ricci ◽  
Elena Scaglione ◽  
Denis Grandgirard ◽  
...  
Keyword(s):  
Sialic Acid ◽  
Corpus Callosum ◽  
Type Strain ◽  
Wild Type Strain ◽  
Lethal Dose ◽  
Sialic Acids ◽  
Wild Type ◽  
Knockout Mutant ◽  
Content Type

ABSTRACTIn serogroup CNeisseria meningitidis, thecssA(siaA) gene codes for an UDP-N-acetylglucosamine 2-epimerase that catalyzes the conversion of UDP-N-acetyl-α-d-glucosamine intoN-acetyl-d-mannosamine and UDP in the first step in sialic acid biosynthesis. This enzyme is required for the biosynthesis of the (α2→9)-linked polysialic acid capsule and for lipooligosaccharide (LOS) sialylation. In this study, we have used a reference serogroup C meningococcal strain and an isogeniccssAknockout mutant to investigate the pathogenetic role of surface-exposed sialic acids in a model of meningitis based on intracisternal inoculation of BALB/c mice. Results confirmed the key role of surface-exposed sialic acids in meningococcal pathogenesis. The 50% lethal dose (LD50) of the wild-type strain 93/4286 was about four orders of magnitude lower than that of thecssAmutant. Compared to the wild-type strain, the ability of this mutant to replicate in brain and spread systemically was severely impaired. Evaluation of brain damage evidenced a significant reduction in cerebral hemorrhages in mice infected with the mutant in comparison with the levels in those challenged with the wild-type strain. Histological analysis showed the typical features of bacterial meningitis, including inflammatory cells in the subarachnoid, perivascular, and ventricular spaces especially in animals infected with the wild type. Noticeably, 80% of mice infected with the wild-type strain presented with massive bacterial localization and accompanying inflammatory infiltrate in thecorpus callosum, indicating high tropism of meningococci exposing sialic acids toward this brain structure and a specific involvement of thecorpus callosumin the mouse model of meningococcal meningitis.

scholarly journals Genetic Determinants of Salmonella enterica Serovar Typhimurium Proliferation in the Cytosol of Epithelial Cells

2016 ◽  
Vol 84 (12) ◽  
pp. 3517-3526 ◽  
Author(s):  
Marie Wrande ◽  
Helene Andrews-Polymenis ◽  
Donna J. Twedt ◽  
Olivia Steele-Mortimer ◽  
Steffen Porwollik ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Salmonella Enterica ◽  
Chloroquine Resistance ◽  
Intestinal Epithelial ◽  
Wild Type ◽  
Genetic Determinants ◽  
Gastrointestinal Infections ◽  
Content Type ◽  
Serovar Typhimurium ◽  
Infectious Cycle

Intestinal epithelial cells provide an important colonization niche forSalmonella entericaserovar Typhimurium during gastrointestinal infections. In infected epithelial cells, a subpopulation ofS. Typhimurium bacteria damage their internalization vacuole, leading to escape from theSalmonella-containing vacuole (SCV) and extensive proliferation in the cytosol. Little is known about the bacterial determinants of nascent SCV lysis and subsequent survival and replication ofSalmonellain the cytosol. To pinpointS. Typhimurium virulence factors responsible for these steps in the intracellular infectious cycle, we screened aS. Typhimurium multigene deletion library in Caco-2 C2Bbe1 and HeLa epithelial cells for mutants that had an altered proportion of cytosolic bacteria compared to the wild type. We used a gentamicin protection assay in combination with a chloroquine resistance assay to quantify total and cytosolic bacteria, respectively, for each strain. Mutants of threeS. Typhimurium genes,STM1461(ydgT),STM2829(recA), andSTM3952(corA), had reduced cytosolic proliferation compared to wild-type bacteria, and one gene,STM2120(asmA), displayed increased cytosolic replication. None of the mutants were affected for lysis of the nascent SCV or vacuolar replication in epithelial cells, indicating that these genes are specifically required for survival and proliferation ofS. Typhimurium in the epithelial cell cytosol. These are the first genes identified to contribute to this step of theS. Typhimurium infectious cycle.

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