Enterocyte-like Cell Line Caco-2 Research Articles

Required characteristics of Paenibacillus polymyxa JB-0501 as potential probiotic

The ability of Paenibacillus polymyxa to inhibit the growth of Escherichia coli generic ATCC 25922 (Escherichia coli ATCC 25922) and to adhere to monolayers of the enterocyte-like human cell line Caco-2 was evaluated. P. polymyxa JB-0501 (P. polymyxa JB-0501), found in a livestock feed probiotic supplement, was compared to P. polymyxa reference strain ATCC 43685 and ATCC 7070 (P. polymyxa ATCC) in terms of carbohydrate utilization and resistance to lysozyme, acid, bile salts, and hydrogen peroxide. JB-0501 grew at pH 4.5 and at H2O2 concentrations less than 7.3μg/ml and presented a higher affinity to hexadecane and decane. Bile salts at 0.2% inhibited the growth of all three strains. P. polymyxa JB-0501 and P. polymyxa ATCC 43865 adhered to Caco-2 cell monolayers. The percentage of cells that adhered ranged from about 0.35 to 6.5% and was partially proportional to the number applied. Contact time (from 15min to 1h) had little impact on adhesion. P. polymyxa JB-0501 inhibited the growth of E. coli ATCC 25922, as proven by the diffusion tests in agar. Taken together, these results suggested that P. polymyxa JB-0501 has the potential probiotic properties to justify its consideration as a livestock feed supplement.

Enterocyte-like Caco-2 cells as a model for in vitro studies of diarrhoeagenic Providencia alcalifaciens invasion

The entry of Providencia alcalifaciens into the enterocyte-like cell line Caco-2 compared to HEp-2 was studied. Of the 22 P. alcalifaciens strains, 13 and 21 were invasive for Caco-2 and HEp-2 cells, respectively. In contrast to HEp-2 cells, P. alcalifaciens was internalised by Caco-2 cells via receptor-mediated endocytosis. Tyrosine kinases play an important role in P. alcalifaciens uptake, also microfilaments and microtubules are engaged in this process. Inhibition of endosome acidification by ammonium chloride did not seem to have any significant effect on P. alcalifaciens invasion. Similarly to Shigella flexnerii, the invasion of Caco-2 cells by these bacteria occurred more effectively through the basolateral pole than through the apical surface of these cells. Plasmid DNA analysis showed the presence of plasmids of 5-172 kb in 13 strains regardless of their invasive ability. The presence of extracellular bacterial protein, most likely a kind of an invasin, is required for the invasion of Caco-2 and HEp-2 cells.

The effects of proinflammatory cytokines on expression of serotonin transporters in human enterocyte-like cell line

Objective To determine the effect of proinflammatory cytokines including interleukin-lbeta (IL-1β) and tumor necrosis factor-Alpha (TNF-α) on human serotonin transporter (SERT) in human enterocyte-like cell line Caco-2.Methods Caco2 cells were cultured for 5 days,then were divided into control group.IL-1β treated group (50 ng/ml) and TNF-α treated group (50ng/ml) for 2.24,48 and 72 hours.The expression of SERT mRNA was detected by RT-PCR at 2,24 and 48 hours and its protein expression was measured by Western blotting at 24,48 and 72 hours.Results The expression of SERT mRNA at 2,24 and 48 hours was lower both in IL-1β treated group (1.393±1.184,1.064±0.625 and 1.013±0.415,respectively) and TNF-α treated group (1.000±0.000,0.829±0.162and 0.945±0.147,respectively) in comparison with control group (2.282±1.367,1.586±0.421 and 1.86 ±O.496,respectively).There was significant difference among three groups (P<0.01).The expression of SERT protein at 24,48 and 72 hours was lower in IL-1β treated group and TNF-α treated group than in control group.Conclusions The IL-1β and TNF-α can inhibit the expressions of SERT mRNA and protein in Caco-2 cells,which indicates that IL-1β and TNF-α may change visceral sensitivity by influencing peripheral 5-hydroxytryptamine levels. Key words: Colonic neoplasms Interleukins; Tumor necrosis factor-Alpha; Serotonin transporter; Cell line,tumor

Lipopolysaccharide induces alteration of serotonin transporter in human intestinal epithelial cells

Intestinal serotoninergic activity and serotonin transporter (SERT) function have been shown to be altered in intestinal inflammatory diseases. Serotonin (5-HT) plays a critical role in the regulation of gastrointestinal physiology. Activity of 5-HT depends on its extracellular availability, partly modulated by SERT that transports 5-HT into the cell. Lipopolysaccharide (LPS) is a component of Gram-negative bacteria outer membrane, which acts as a potent activator of the inflammatory system in the intestine. The aim of this work was to determine, in the enterocyte-like cell line Caco-2, whether LPS treatment affects serotoninergic activity by acting on SERT. The results demonstrate that LPS treatment diminishes SERT activity in a dose- and period-dependent way. The kinetic study shows that V(max) was significantly reduced after treatment with LPS. The LPS effect on 5-HT uptake was, in part, mediated by protein kinase C (PKC) activation. The molecular expression of SERT revealed that LPS treatment did not affect the mRNA level or the SERT protein content in cell homogenate. The level of SERT protein, however, was reduced on brush border membrane. The LPS effect might be due to an alteration of the intracellular traffic of SERT which may, in part, be mediated by PKC activity.

Lipopolysaccharide-binding protein: localization in secretory granules of Paneth cells in the mouse small intestine

Lipopolysaccharide (LPS)-binding protein (LBP) is an acute-phase protein involved in the host's response to endotoxin and mainly synthesized and secreted to the blood by the liver. But in addition, LBP is also made by extrahepatic cells, including the enterocyte-like cell line Caco-2. To study in closer detail the synthesis and storage of LBP in the intestinal mucosal epithelium, we performed an immunolocalization of LBP in mouse small intestine. By immunofluorescence microscopy, an antibody recognizing the 58-60 kDa protein of LBP distinctly labeled a small population of cells located deep into the crypts. This cell population was also positive for lysozyme and alpha-defensin 4, identifying Paneth cells as the main intestinal LBP-producing cells. By immunogold electron microscopy, intense labeling was observed in the secretory granules of these cells. We conclude that Paneth cells express LBP together with other proteins acting in the innate immune response of the gut, such as lysozyme, defensins and intelectin.

Comparison of cytokine modulation by natural peroxisome proliferator–activated receptor γ ligands with synthetic ligands in intestinal-like Caco-2 cells and human dendritic cells—potential for dietary modulation of peroxisome proliferator–activated receptor γ in intestinal inflammation

BackgroundPeroxisome proliferator–activated receptor γ (PPARγ) plays a role in the regulation of intestinal inflammation and is activated by both natural (polyunsaturated fatty acid; PUFAs) and synthetic (troglitazone) ligands. The fatty acid content of defined formula diets may play a role in mediating the antiinflammatory effect, but the mechanism is unclear. ObjectiveWe evaluated to what extent the effect of PUFAs on intestinal inflammation is mediated via PPARγ. DesignThe human enterocyte-like cell line Caco-2 and human dendritic cells were stimulated by interleukin (IL) 1β and lipoprotein polysaccharide, respectively, in the presence of PPARγ agonists (troglitazone or PUFAs) or antagonist (GW9662). Five PUFAs were tested: α-linolenic acid (ALA), conjugated linoleic acid (CLA), docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and γ-linolenic acid (GLA). Cytokine production was measured by enzyme-linked immunosorbent assay and PPARγ, I-κB, and inducible nitric oxide synthase (iNOS) expression by Western blot. ResultsIn Caco-2 cells, IL-6 secretion was significantly decreased by troglitazone, DHA, EPA, and GLA. IL-8 production was significantly decreased by troglitazone, ALA, DHA, EPA, and GLA. PPARγ expression was significantly increased by troglitazone, DHA, and EPA. iNOS expression was significantly decreased by troglitazone, DHA, and EPA. Troglitazone and PUFAs at 0.1 μmol/L tended to increase the expression of I-κB. Addition of GW9662 reversed the effect of troglitazone and PUFAs at 0.1 μmol/L on IL-8 production and decreased the expression of PPARγ. EPA and DHA also modulated the dendritic cell response to lipoprotein polysaccharide. ConclusionsThe tested PUFAs exerted an antiinflammatory effect in vitro in both models. This effect of PUFAs in Caco-2 cells is similar to that of troglitazone on intestinal inflammation mediated by PPARγ, and the potency of the antiinflammatory effect is linked to the number of double bonds.

Regulation of the human serotonin transporter mediated by long‐term action of serotonin in Caco‐2 cells

The aim of this study was to determine the effect of long-term serotonin (5-hydroxytryptamine, 5-HT) treatment on the human serotonin transporter (hSERT) function and its expression. This study was carried out in the enterocyte-like cell line Caco-2. These cells constitutively express the hSERT and have been shown to be an excellent model for the study of this protein. We measured serotonin transport, levels of mRNA expression and of the SERT protein after treating the cells with serotonin. Serotonin treatment diminished hSERT activity in a concentration and period-dependent way by increasing the K(t) value and reducing V(max). This inhibition was reversible and was not mediated by either the action of 5-HT(2), 5-HT(3) or 5-HT(4) receptors, or by the intracellular second messengers, protein kinase C and cAMP. 5-HT did not seem to affect either the mRNA level of the SERT or the protein transporter measured in either the membrane or the cell lysate. The 5-HT treatment effect was additive to the inhibitory effect of treatment with a low concentration of citalopram and fluoxetine. Nevertheless, 5-HT did not increase the inhibition yielded by treatment with high concentration citalopram. The chronic increase in serotonin in the extracellular medium diminishes the function of the SERT. This effect seems to be due to an effect on the transporter molecule itself in the membrane, without altering protein synthesis, intracellular traffic, or its availability.

Effect of long-term fluoxetine treatment on the human serotonin transporter in Caco-2 cells

Fluoxetine is a selective serotonin reuptake inhibitor (SSRI) broadly used in the treatment of human mood disorders and gastrointestinal diseases involving the serotoninergic system. The effectiveness of this therapy depends on repeated long-term treatment. Most of the long-term studies in vivo of SSRI effects on serotoninergic activity have focused on their effects on autoreceptors or postsynaptic receptors. The chronic effect of SSRIs on the activity of the serotonin transporter (SERT) has been less studied and the results have been contradictory. The aim of this study was to determine the specific effect of long-term fluoxetine treatment on human serotonin transporter (hSERT) in vitro, by using the human enterocyte-like cell line Caco-2. Results show that fluoxetine diminished the 5-HT uptake in a concentration-dependent way and that this effect was reversible. Fluoxetine affected mainly the hSERT transport rate by reducing the availability of the transporter in the membrane with no significant alteration of either the total hSERT protein content or the hSERT mRNA level. These results suggest that the effect of fluoxetine on the expression of hSERT is post-translational and has shown itself to be independent of PKC and PKA activity. This study may be useful to clarify the effect of the long-term fluoxetine therapy in both gastrointestinal and central nervous system disorders.

Complementation of Listeria seeligeri with the plcA-prfA genes from L. monocytogenes activates transcription of seeligerolysin and leads to bacterial escape from the phagosome of infected mammalian cells.

Infection experiments have shown that the avirulent species Listeria seeligeri invaded the enterocyte-like cell line Caco-2 with low efficiency but was unable to escape from the phagosome. Introduction of the listeriolysin gene (hly) from L. monocytogenes into L. seeligeri via a recombinant plasmid did not change these characteristics. No measurable transcription of this gene or of the structurally intact chromosomal seeligerolysin gene (lso) was detected. Transformation with a plasmid carrying the bicistronically transcribed plcA-prfA genes from L. monocytogenes resulted in the efficient expression of the plasmid-encoded transcription activator PrfA, a readily detectable synthesis of seeligerolysin and the escape of the bacteria from the phagosome of infected mammalian cells, followed by intracytoplasmic multiplication.

Sucrase-Isomaltase Gene Expression Is Inhibited by Mutant Hepatocyte Nuclear Factor (HNF)-1.ALPHA. and Mutant HNF-1.BETA. in Caco-2 Cells

Hepatocyte nuclear factor (HNF)-1alpha and HNF-1beta are concerned in sucrase-isomaltase (SI) gene expression, and directly bind two sites (SIF2, SIF3) of the promoter of the SI gene. However, it is not completely clear that HNF-1alpha and HNF-1beta play a role in regulation of SI gene expression. To clarify mechanisms of SI gene expression regulated by HNF-1alpha and HNF-1beta, we established four stable cell lines based on enterocyte-like cell line Caco-2, in which wild HNF-1alpha or wild HNF-1beta, or else mutant HNF-1alphaT539fsdelC or mutant HNF-1betaR177X was overexpressed. In the HNF-1alphaT539fsdelC cells and HNF-1betaR177X cells, but not in the wild HNF-1alpha cells and wild HNF-1beta cells, SI gene expression and enzyme activity were significantly diminished compared with that in Caco-2 cells. Moreover, to clarify whether or not stable cell differentiation was influenced by overexpression of these transgenes, alkaline phosphatase (ALP) gene expression and enzyme activity were measured. There were no changes in ALP gene expression or enzyme activity in these cells. These observations suggest that mutant HNF-1alphaT539fsdelC and mutant HNF-1betaR177X inhibits SI gene at the transcriptional level, resulting in decreased SI enzyme activity in Caco-2 cells. We propose that both HNF-1alpha and HNF-1beta would contribute to constitutive expression of the SI gene in the differentiated state in Caco-2 cells.

The 35S CaMV plant virus promoter is active in human enterocyte-like cells

The 35S cauliflower mosaic virus (CaMV) promoter is commonly used to drive transgene expression in the genetically engineered (GE) crop plants that have been commercialized so far. Whether, and how far, the 35S promoter might be active in mammalian cells has been scientifically unsettled and controversial. Very recently it was established that the 35S promoter is transcriptionally active following transient reporter gene transfections in continuous cell lines of human [J Biotechnol 103:197–202, 2003] and hamster ovary [Environ Biosafety Res 3:41–47, 2004] fibroblasts. The initial exposure of a human organism to DNA from GE food takes place in the gastrointestinal tract (GIT). Hence, we have now investigated the promoter capacity of 35S in human enterocyte-like cells. We constructed expression vectors with 35S promoter inserted in front of two reporter genes encoding firefly luciferase and green fluorescent protein (GFP), respectively, and performed transient transfection experiments in the human enterocyte-like cell line Caco-2. It was demonstrated that the 35S CaMV promoter was able to drive the expression of both reporter genes to significant levels, although the protein expression levels might seem modest compared to those obtained with the strong promoters derived from human cytomegalo virus (hCMV) and simian virus 40 (SV40). Furthermore, computer-based searches of the 35S CaMV DNA sequence for putative mammalian transcription factor binding motifs gave a high number of hits. Some of the identified motifs indicate that transcriptional activation by the 35S CaMV promoter may be stronger in other human and animal cell types than in those investigated so far.

Bifidobacterium Lactis sp. 420 Up-Regulates Cyclooxygenase (Cox)-1 and Down-Regulates Cox-2 Gene Expression in a Caco-2 Cell Culture Model

: Cyclooxygenases (Cox) -1 and -2 play important roles in gastrointestinal health; chronic overexpression of Cox-2 is associated with inflammatory and cancerous disease, whereas Cox-1 is expressed constitutively. We studied the effects of two probiotic (Bifidobacterium lactis sp. 420 and Lactobacillus acidophilus) and two control microorganisms (Escherichia coli and Salmonella enteritidis) and four microbial metabolites (acetate, butyrate, lactate and propionate) on the expression levels of the Cox isoforms in the enterocyte-like cell line Caco-2. Butyrate, which is anticarcinogenic, resulted in an 85% down-regulation of Cox-2 and a 37-fold increase in Cox-1 transcription. Propionate gave similar results (72% reduction of Cox-2, 23-fold induction of Cox-1), but lactate and acetate had no effect on Cox expression profile. Bifidobacterium sp. 420, which produces acetate and lactate but no butyrate or propionate, shared the Cox-1-increasing and Cox-2-silencing properties of butyrate and propionate, whereas L. acidophilus was similar to E. coli and S. enteritidis in having no effect on the Cox-1/Cox-2 ratio. For the first time, we therefore demonstrate evidence for a direct relationship between a probiotic bacterial strain and host Cox expression profile, suggesting that modulation of Cox expression may be an important factor in the potential anti-inflammatory and anticarcinogenic properties of some probiotics.

Translocation of Yersinia entrocolitica across reconstituted intestinal epithelial monolayers is triggered by Yersinia invasin binding to beta1 integrins apically expressed on M-like cells.

Yersinia enterocolitica cross the intestinal epithelium via translocation through M cells, which are located in the follicle-associated epithelium (FAE) of Peyer's patches (PP). To investigate the molecular basis of this process, studies were performed using a recently developed in vitro model, in which the enterocyte-like cell line Caco-2 and PP lymphocytes are co-cultured in order to establish FAE-like structures including M cells. Here, we demonstrate that Y. enterocolitica does not adhere significantly to the apical membrane of differentiated enterocyte-like Caco-2 cells that express binding sites for Ulex europaeus agglutinin (UEA)-1. In contrast, Y. enterocolitica adhered to, and was internalized by, cells that lacked UEA-1 binding sites and displayed a disorganized brush border. These cells were considered to be converted to M-like cells. Further analysis revealed that part of these cells expressed beta1 integrins at their apical surface and, as revealed by comparison of wild-type and mutant strains, interacted with invasin of Y. enterocolitica. Consistently, anti-beta1 integrin antibodies significantly inhibited internalization of inv-expressing yersiniae. Experiments with Yersinia mutant strains deficient in YadA or Yop secretion revealed that these virulence factors play a minor role in this process. After internalization, yersiniae were transported within LAMP-1-negative vacuoles to, and released at, the basal surface. Internalization and transport of yersiniae was inhibited by cytochalasin D, suggesting that F-actin assembly is required for this process. These results provide direct evidence that expression of beta1 integrins at the apical surface of M cells enables interaction with the invasin of Y. enterocolitica, and thereby initiates internalization and translocation of bacteria.

Actin mediates Encephalitozoon intestinalis entry into the human enterocyte-like cell line, Caco-2

Microsporidia are spore-forming obligate intracellular eucaryotes that parasitize eukaryotic cells.Encephalitozoon intestinalis (formerly Septata intestinalis) is a microsporidian species of emerging medical importance, responsible for chronic diarrhoea in immunocompetent patients and enteritis and systemic infections in HIV-1 infected patients. Infection of host enterocytes has been demonstrated in HIV-1-infected patients. However, the mechanisms of entry ofE. intestinalis into host enterocytes have not been studied and remain hypothetically based on diacytosis, a model involving the injection of microsporidian sporoplasm through the polar tubule into the host cell. An electron microscopy based study recently challenged this hypothesis. We studied the entry of E. intestinalis into intestinal epithelial cells by infecting the human enterocyte-like cell line Caco-2. Entry was mediated by directed phagocytosis, as suggested by the inhibiting effect of cytochalasin D on E. intestinalis uptake, colocalization of E. intestinalis and F-actin and engulfment of E. intestinalis into Caco-2 cell protrusions. Confocal- and electron microscopy observations also suggested that after initial contacts through the posterior pole of the microsporidian spore, the basolateral surface of Caco-2 cells may be the portal of entry for E. intestinalis sporoplasm. Our observations allowed us to propose a new, actin-based model to describe the entry of microsporidia into enterocytes.

Characterization of an enterotoxigenic Escherichia coli strain from Africa expressing a putative colonization factor.

An enterotoxigenic Escherichia coli (ETEC) strain of serotype O114:H- that expressed both heat-labile and heat-stable enterotoxins and tested negative for colonization factors (CF) was isolated from a child with diarrhea in Egypt. This strain, WS0115A, induced hemagglutination of bovine erythrocytes and adhered to the enterocyte-like cell line Caco-2, suggesting that it may elaborate novel fimbriae. Surface-expressed antigen purified by differential ammonium sulfate precipitation and column chromatography yielded a single protein band with M(r) 14,800 when resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (16% polyacrylamide). A monoclonal antibody against this putative fimbrial antigen was generated and reacted with strain WS0115A and also with CS1-, CS17-, and CS19-positive strains in a dot blot assay. Reactivity was temperature dependent, with cells displaying reactivity when grown at 37 degrees C but not when grown at 22 degrees C. Immunoblot analysis of a fimbrial preparation from strain WS0115A showed that the monoclonal antibody reacted with a single protein band. Electron microscopy and immunoelectron microscopy revealed fimbria-like structures on the surface of strain WS0115A. These structures were rigid and measured 6.8 to 7.4 nm in diameter. Electrospray mass-spectrometric analysis showed that the mass of the purified fimbria was 14,965 Da. The N-terminal sequence of the fimbria established that it was a member of the CFA/I family, with sequence identity to the amino terminus of CS19, a new CF recently identified in India. Cumulatively, our results suggest that this fimbria is CS19. Screening of a collection of ETEC strains isolated from children with diarrhea in Egypt found that 4.2% of strains originally reported as CF negative were positive for this CF, suggesting that it is biologically relevant in the pathogenesis of ETEC.

The Anti-invasive Effect of Bovine Lactoferrin Requires an Interaction with Surface Proteins of Listeria Monocytogenes

The anti-invasive effect of bovine lactoferrin (BLf) and of bovine transferrin (BTf) towards L. monocytogenes, an intracellular facultative food-borne pathogen, was assayed in the enterocyte-like cell line Caco-2. When 0.5 mg/ml BLf were added during the infection time or preincubated with bacteria the number of internalized bacteria was noticeably decreased whereas BLf was ineffective when preincubated with the enterocytes or added post infection. BTf was deprived of any effect. Results from direct binding and Western blotting assays provided evidence that two L. monocytogenes surface proteins, of approximately 80 and 60 kDa, specifically reacted with BLf. These findings strongly support the hypothesis that the antiinvasive mechanism of BLf is due to its interaction with bacterial surfaces, but not to its binding with eukaryotic cells.

Glucose and amino acid metabolism in Caco-2 cells maintained in a serum- and hormone-free medium.

Glucose and amino acid metabolism in a human enterocyte-like cell line (Caco-2) cultured in a serum- and hormone-free medium was examined and effects of epidermal growth factor (EGF) on these cells determined. These cells took up glutamine and converted it to alanine and proline. EGF stimulated the metabolism significantly.

Lectin reactivity and virulence among strains of Listeria monocytogenes determined in vitro using the enterocyte-like cell line Caco-2.

Forty-six cultures of Listeria monocytogenes (including clinical, food and collection strains) were serotyped, characterized for motility, haemolysis and phospholipase activities and tested for lectin agglutination using a four-lectin set. Lectin reactivity (i.e. agglutination by one or more of the four lectins) was observed in all 12 clinical isolates, 16 of the 23 food isolates and eight of the 11 collection strains. Virulence was evaluated in vitro based on strains' ability to invade the human enterocyte-like cell line Caco-2. In gentamicin survival experiments, recovery of viable intracellular bacteria among lectin-unreactive strains was usually 100-1000-fold lower than among lectin-reactive haemolytic strains, and lower than among nonhaemolytic strains. Considerable cytopathogenic effects were produced by lectin-reactive haemolytic strains in trypan-blue-stained cell monolayers, whereas lectin-unreactive and nonhaemolytic strains produced no detectable cytopathogenic effect. Among lectin-reactive strains, the number of listerial cells associated with Caco-2 monolayers was more than tenfold greater than among lectin-unreactive strains. Cell invasion was inhibited by pretreatment of Caco-2 cells with sugars recognized by the lectins or of listeriae with enzymes which removed the same sugars from the bacterial surface. The results suggest that the study of lectin interactions could be helpful in understanding the pathogenicity potential of isolates of food and environmental origin.

Complementation of Listeria seeligeri with the plcA- prfA genes from L. monocytogenes activates transcription of seeligerolysin and leads to bacterial escape from the phagosome of infected mammalian cells

Infection experiments have shown that the avirulent species Listeria seeligeri invaded the enterocyte-like cell line Caco-2 with low efficiency but was unable to escape from the phagosome. Introduction of the listeriolysin gene ( hly) from L. monocytogenes into L. seeligeri via a recombinant plasmid did not change these characteristics. No measurable transcription of this gene or of the structurally intact chromosomal seeligerolysin gene ( lso) was detected. Transformation with a plasmid carrying the bicistronically transcribed plcA- prfA genes from L. monocytogenes resulted in the efficient expression of the plasmid-encoded transcription activator PrfA, a readily detectable synthesis of seeligerolysin and the escape of the bacteria from the phagosome of infected mammalian cells, followed by intracytoplasmic multiplication.

Iron availability affects entry of Listeria monocytogenes into the enterocytelike cell line Caco-2.

The influence of iron on the entry of Listeria monocytogenes into Caco-2 cells was studied. Iron availability was found to modify the surface hydrophobicity and protein profile of L. monocytogenes, with the result that cell invasion strongly increased upon bacterial growth in iron-rich medium. The enhanced invasive capability of iron-overloaded L. monocytogenes cells correlates to the higher-level expression of the inlAB virulence genes, which were positively iron regulated at the transcriptional level.