WEB shape modifications: angiography-histopathology correlations in rabbits

BACKGROUND

WEB Shape Modification (WSM) over time is frequent after aneurysm treatment. In this study, we explored the relationship between histopathological changes and angiographic evolution over time in experimental aneurysms in rabbits treated with the Woven EndoBridge (WEB) procedure.

METHODS

Quantitative WSM was assessed using flat-panel computed tomography (FPCT) during follow-up by calculating height and width ratio (HR, WR), defined as the ratio between either measurement at an index time point and the measurement immediately after WEB implantation. The index time point varied from 1 day to 6 months. HR and WR were evaluated with angiographic and histopathological assessments of aneurysm healing.

RESULTS

Final HR of devices varied from 0.30 to 1.02 and final WR varied from 0.62 to 1.59. Altogether, at least 5% of HR and WR variations were observed in 37/40 (92.5%) and 28/40 (70%) WEB devices, respectively, at the time of final assessment. There was no significant correlation between complete or incomplete occlusion groups and HR or WR (p=0.15 and p=0.43). Histopathological analysis revealed a significant association between WR and aneurysm healing and fibrosis 1 month following aneurysm treatment (both p<0.05).

CONCLUSION

Using longitudinal FPCT assessment, we observed that WSM affects both the height and width of the WEB device. No significant association was found between WSM and aneurysm occlusion status. Although presumably a multifactorial phenomenon, the histopathological analysis highlighted a significant association between width variations, aneurysm healing and fibrosis in the first month following aneurysm treatment.

Comparison of arterial wall integration of different flow diverters in rabbits: The CICAFLOW study

BACKGROUND AND PURPOSE

New coated flow diverters (FDs) claim antithrombotic properties and increased arterial wall integration. The aim of this study is to compare in vivo endothelial coverage of coated and uncoated FD in the context of different antiplatelet regimens.

METHODS

Different FDs (Silk Vista - SV, Pipeline with Shield technology - PED shield and Surpass Evolve - SE) were implanted in the aorta of rabbits, all 3 in each animal with 3 different antiplatelet regimens: no antiplatelet therapy, aspirin alone, or aspirin and ticagrelor. Four weeks after FD implantation, angiography, flat-panel CT, and optical coherence tomography (OCT) were performed before harvesting the aorta. Extensive histopathology analyses were performed including environmental scanning electron microscopy (ESEM), multiphoton microscopy (MPM) and histological staining with qualitative and/or quantitative assessment of device coverage.

RESULTS

All 23 FDs that were implanted remained patent without hyperplasia. Qualitative stent coverage assessment revealed that there were no statistically significant differences between the FD groups (p = 0.19, p = 0.45, p = 0.40, and p = 0.84 for OCT, ESEM, MPM and histology, respectively). Quantitative neointimal measurement of histological sections also showed similar results in all 3 FD groups (p = 0.70). However, there were significant differences between the 3 groups of antiplatelet regimens (p = 0.07) with a higher rate in the no antiplatelet group (p = 0.05 versus aspirin alone and p = 0.03 versus aspirin and ticagrelor).

CONCLUSION

Our study provides evidence that FD integration into the arterial wall is similar with coated (PED shield) and uncoated devices (SV, SE), regardless of the antiplatelet regimen. FD integration with specific surface coverage should be promoted.

TRIAL REGISTRATION

APAFIS #2022011215518538.

Fucoidan-coated coils improve healing in a rabbit elastase aneurysm model

BACKGROUND

Recanalization of coiled aneurysms remains unresolved. To limit aneurysm recanalization after embolization with coils, we propose an innovative approach to optimize aneurysm healing using fucoidan-coated coils.

OBJECTIVE

To evaluate the short-term efficacy and long-term safety of the new coil system with conventional angiography, histology, and multiphoton microscopy for follow-up of fibrosis and neointima formation.

METHODS

We conducted a feasibility study on rabbit elastase-induced aneurysms. Embolization was carried out with bare platinum coils, fucoidan-coated coils, or dextran-coated coils. Aneurysms were controlled after 1 month by digital subtraction angiography (DSA). Aneurysm samples were collected and processed for histological analysis. Aneurysm healing and fibrosis were measured by quantifying collagen according to the histological healing score by combining standard light microscopy and multiphoton imaging. We divided 27 rabbits into three groups: bare platinum group, fucoidan group, and dextran group as controls.

RESULTS

Angiographic grading showed a trend toward less recanalization in the fucoidan group, although there were no significant differences among the three groups (P=0.21). Histological healing was significantly different according to the presence of more collagen in the neck area of aneurysms in the fucoidan group versus the bare platinum group (P=0.011), but not in the dextran group. Histological index was significantly better at the aneurysm neck in the fucoidan group than in the bare platinum group (P=0.004). Collagen organization index was also significantly better in the fucoidan group than in the bare platinum group (P=0.007).

CONCLUSION

This proof-of-concept study demonstrated the feasibility and efficacy of treatment with fucoidan-coated coils to improve aneurysm healing. The results in this rabbit in vivo model showed that fucoidan-coated coils have the potential to improve healing following endovascular treatment.

Bioactive refinement for endosaccular treatment of intracranial aneurysms

Endovascular treatment is the first-line therapy for most intracranial aneurysms; however, recanalisation remains a major limitation. Developments in bioengineering and material science have led to a novel generation of coil technologies for aneurysm embolisation that address clinical challenges of aneurysm recurrence. This review presents an overview of modified surface coil technologies and summarises the state of the art regarding their efficacy and limitations based on experimental and clinical results. We also present potential perspectives to develop biologically optimised devices.

Mycobiota dynamics and mycotoxin detection in PGI Salame Piemonte

AIMS

The complex mycobiota that colonizes traditional fermented sausages plays an important role in the organoleptic properties of such products. The aim of the present study was to investigate fungal diversity and mycotoxin production during maturation of PGI Salame Piemonte.

METHODS AND RESULTS

Casing and meat samples were collected at five sampling times from three different batches produced in the same factory and analysed using culture-dependent and independent approaches. Penicillium nalgiovense, which was deliberately inoculated, and Debaryomyces hansenii were the most dominant taxa in casings. Several other fungi mainly belonging to Penicillium crustosum, Penicillium glabrum, Penicillium nordicum, Cladosporium spp., Candida sake, Candida zeylanoides and Yarrowia divulgata were also identified. The casing mycobiota was compared to that of the meat using a metataxonomic approach and a higher fungal diversity was observed in meat as compared to casings. Mycotoxins and penicillin G were monitored using QTOF LC-MS and only trace amounts of roquefortine C were detected in two batches.

CONCLUSIONS

The present study highlighted the diversity of Salame Piemonte mycobiota and the important contribution of autochthonous fungi to its diversity. The absence of mycotoxins and penicillin G confirmed the high hygienic quality of the studied product regarding fungal and mycotoxin contamination.

SIGNIFICANCE AND IMPACT OF THE STUDY

For the first time, this study provides insights about Salame Piemonte mycobiota, which together with the bacterial microbiota and Salame Piemonte process specifications, are responsible for the product organoleptic properties.

212Pb α-Radioimmunotherapy Targeting CD38 in Multiple Myeloma: A Preclinical Study

Multiple myeloma (MM) is a plasma cell cancer and represents the second most frequent hematologic malignancy. Despite new treatments and protocols, including high-dose chemotherapy associated with autologous stem cell transplantation, the prognosis of MM patients is still poor. α-radioimmunotherapy (α-RIT) represents an attractive treatment strategy because of the high-linear-energy transfer and short pathlength of α-radiation in tissues, resulting in high tumor cell killing and low toxicity to surrounding tissues. In this study, we investigated the potential of α-RIT with ²¹²Pb-daratumumab (anti-hCD38), in both in vitro and in vivo models, as well as an antimouse CD38 antibody using in vivo models. Methods: Inhibition of cell proliferation after incubation of the RPMI8226 cell line with an increasing activity (0.185-3.7 kBq/mL) of ²¹²Pb-isotypic control or ²¹²Pb-daratumumab was evaluated. Biodistribution was performed in vivo by SPECT/CT imaging and after death. Dose-range-finding and acute toxicity studies were conducted. Because daratumumab does not bind the murine CD38, biodistribution and dose-range finding were also determined using an antimurine CD38 antibody. To evaluate the in vivo efficacy of ²¹²Pb-daratumumab, mice were engrafted subcutaneously with 5 × 10⁶ RPMI8226 cells. Mice were treated 13 d after engraftment with an intravenous injection of ²¹²Pb-daratumumab or control solution. Therapeutic efficacy was monitored by tumor volume measurements and overall survival. Results: Significant inhibition of proliferation of the human myeloma RPMI8226 cell line was observed after 3 d of incubation with ²¹²Pb-daratumumab, compared with ²¹²Pb-isotypic control or cold antibodies. Biodistribution studies showed a specific tumoral accumulation of daratumumab. No toxicity was observed with ²¹²Pb-daratumumab up to 370 kBq because of lack of cross-reactivity. Nevertheless, acute toxicity experiments with ²¹²Pb-anti-mCD38 established a toxic activity of 277.5 kBq. To remain within realistically safe treatment activities for efficacy studies, mice were treated with 185 kBq or 277.5 kBq of ²¹²Pb-daratumumab. Marked tumor growth inhibition compared with controls was observed, with a median survival of 55 d for 277.5 kBq of ²¹²Pb-daratumumab instead of 11 d for phosphate-buffered saline. Conclusion: These results showed ²¹²Pb-daratumumab to have efficacy in xenografted mice, with significant tumor regression and increased survival. This study highlights the potency of α-RIT in MM treatment.

Monascus spp. used in wheat kernel solid-state fermentations: growth, extrolite production and citrinin cytotoxicity

Monascus fermentation products can be consumed as food or feed supplements or used as food colouring or flavouring agents. In this study, qPCR and Q-TOF LC/MS methods were developed to monitor Monascus ruber and Monascus purpureus growth and extrolite (lovastatin, mevastatin, as well as the regulated mycotoxin, citrinin (CIT)) production, respectively. Wheat kernels were inoculated with one strain of each species during a solid-state fermentation followed over 63 days. Different growth and extrolite production patterns were clearly observed for the 2 tested strains. After 63 days, high lovastatin levels (up to 0.5 mg/g) were reached for M. ruber wheat fermented kernels while M. purpureus only yielded 0.1 mg/g of lovastatin at best, suggesting that M. ruber may be a better candidate for lovastatin production in a wheat-based model. Mevastatin levels were low and stable for both species. However, M. ruber fermented wheat kernels also contained the highest CIT content, up to 4.2 μg/g, i.e. at levels above the regulation threshold set by the European Union. CIT toxicity was then determined in vitro on bovine kidney cells, showing an IC10 of 6.10-4 M. At maximum concentrations encountered during solid-state fermentation, CIT toxicity was very low under chronic exposure.

New insights into the haemo- and coelo-microbiota with antimicrobial activities from Echinodermata and Mollusca

AIMS

The aim of this study was to investigate the diversity of bacteria with antimicrobial activity present in the coelomic fluid and haemolymph of wild and healthy echinodermata and mollusca.

METHODS AND RESULTS

Collection expeditions of healthy marine molluscs and echinoderms were conducted in the Glenan archipelago in spring 2014. Members of the culturable microbiota present in the haemolymph, (haemo-microbiota) of Haliotis tuberculata (gastropoda, abalone) and Mytilus edulis (bivalvia, mussel), as well as in the coelomic fluid (coelo-microbiota) of Echinus esculentus (echinoidea, sea urchin) and Holothuria forskali (Holothuroidea, holothurian) were screened for antimicrobial activity, and further identified using 16S rRNA sequencing. Except for E. esculentus, culturable bacteria in the internal fluids of all studied organisms (mussel, abalone and holothurian) were more abundant than in seawater. The haemo- and coelo-microbiota with antimicrobial activity differed significantly between host species, in terms of abundance and diversity. Indeed, higher numbers were isolated from mussel than from abalone haemolymph. Moreover, in mussels and holothurians, bacteria with antimicrobial activities were predominantly Vibrio spp. (respectively 55 and 45%), while Pseudoalteromonas spp. were the most abundant (50%) in abalone haemolymph. Nevertheless, the activity spectra of these bacteria mainly included marine pathogens affiliated to the Vibrio genus.

CONCLUSION

The haemo- and coelo-microbiota with antimicrobial activities were significantly related to their host species and differed in terms of abundance and diversity. These bacteria may play a key role in host homeostasis against pathogens.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study brings new knowledge on the diversity of bacteria present in the internal fluids of two marine molluscs and two echinoderms and their antimicrobial activities towards marine pathogens.

Individual and combined effects of roquefortine C and mycophenolic acid on human monocytic and intestinal cells

Roquefortine C (ROC) and mycophenolic acid (MPA) are secondary metabolites produced by various fungal species. It is known that both ROC and MPA may co-occur in raw materials or food. However, to date there is a lack of information regarding their toxicity. In this study, ROC and/or MPA cytotoxicity was evaluated on human intestinal (Caco-2) and monocytic cell cultures (THP-1 and CD14+). After 48 h single mycotoxin exposure, viability tests showed that monocytes (THP-1 and CD14+) were more sensitive to ROC (inhibitory concentration 50% (IC50)=55 and 45 μM, respectively) than to MPA (IC50>780 μM). IC50 values determined from ROC and MPA mono-exposure experiments on Caco-2 cells were >100 and >780 μM, respectively. Caco-2 cell viability was significantly reduced after 48 h co-exposure at high ROC/MPA concentrations. A synergistic effect was observed at 10/78, 25/780 and 50/780 μM ROC/MPA concentrations, while an additive effect was seen at 100/780 μM. THP-1 apoptosis rate increased after 3 and/or 6 h single ROC (from 10 to 100 μM) and MPA (780 μM) exposures in a dose-dependent manner. Co-exposure to 100/780 μM of ROC/MPA led to an increase in the THP-1 apoptotic cell population. No apoptosis mechanism was observed on Caco-2 cells. This is the first time that combined ROC and MPA cytotoxic effects, as well as the associated mechanisms are investigated.

Application of denaturing high-performance liquid chromatography (DHPLC) for yeasts identification in red smear cheese surfaces

AIMS

To evaluate and optimize the use of denaturing high-performance liquid chromatography (DHPLC) for yeasts identification in red smear cheese surfaces.

METHODS AND RESULTS

The resolution of DHPLC was first evaluated and optimized using a mixture of PCR amplicons of the internal transcribed spacer 2 (ITS2) region of 19 yeast reference strains representing 18 species that are common in the cheese microbiota. Sixteen of the 18 yeast species could be resolved by combining runs at temperatures of 57.5 and 59 degrees C. Then, DHPLC was used to investigate the yeast microbiota of pasteurized Maroilles, Munster and Livarot cheese surfaces by comparing their peak profiles with our reference yeast database and by collecting/sequencing of peak fractions. Debaryomyces hansenii and Geotrichum candidum for Munster and Maroilles cheeses, and Candida catenulata, Candida intermedia and G. candidum for Livarot cheese were identified using the reference database and collecting/sequencing of peak fractions.

CONCLUSIONS

DHPLC technique was found to have good resolution properties and to be useful for investigating the yeast microbiota of red smear cheese surfaces.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first time that DHPLC is applied to study the yeast microbiota of red smear cheese surfaces.

Assessment of the microbial diversity at the surface of Livarot cheese using culture-dependent and independent approaches

The microbial diversity of the surface of a commercial red-smear cheese, Livarot cheese, sold on the retail market was studied using culture-dependent and independent approaches. Forty yeasts and 40 bacteria from the cheese surface were collected, dereplicated using single-strand conformation polymorphism (SSCP) analysis and identified using rRNA gene sequencing for the culture-dependent approach. The culture-independent approach involved cloning and sequencing of the 16S rRNA gene and SSCP analysis from total DNA extracted from the cheese. The most dominant bacteria were Microbacterium gubbeenense, Leucobacter komagatae and Gram-negative bacteria from the Gamma-Proteobacteria class. Fluorescence in situ hybridization (FISH) analysis was also used to study the cheese microbial diversity with class-level and specific rRNA-targeted probes for bacteria and yeasts, respectively. FISH analysis confirmed that Gamma-Proteobacteria were important microorganisms in this cheese. Four specific FISH probes targeting the dominant yeasts present in the cheese, Candida catenulata, Candida intermedia, Geotrichum spp. and Yarrowia lipolytica, were also designed and evaluated. These probes allowed the detection of these yeasts directly in cheese. The use of the rRNA gene-based approach combined with FISH analysis was useful to investigate the diversity of a surface microbial consortium from cheese.

Stability of the biodiversity of the surface consortia of Gubbeen, a red-smear cheese

A total of 1,052 bacteria and 828 yeasts were isolated from the surface flora of 6 batches of Gubbeen cheese made in 1996-1997 and 2002-2003. Stability of the microflora was evaluated over time and also during ripening at 4, 10, and 16 d (batches 4, 5, and 6) or at 4, 16, 23, and 37 d (batches 1, 2, and 3). Bacteria were identified using pulsed-field gel electrophoresis, repetitive extragenic palindromic-PCR, and 16S rRNA gene sequencing, and yeasts were identified by Fourier transform infrared spectroscopy. The bacteria included at least 17 species, of which the most common were Staphylococcus saprophyticus (316 isolates), Corynebacterium casei (248 isolates), Brevibacterium aurantiacum (187 isolates), Corynebacterium variabile (146 isolates), Microbacterium gubbeenense (55 isolates), Staphylococcus equorum/cohnii (31 isolates), and Psychrobacter spp. (26 isolates). The most common yeasts were Debaryomyces hansenii (624 isolates), Candida catenulata (135 isolates), and Candida lusitaniae (62 isolates). In all batches of cheese except batch 2, a progression of bacteria was observed, with staphylococci dominating the early stages of ripening and coryneforms the later stages. No progression of yeast was found. Pulsed-field gel electrophoresis showed that several different strains of the 5 important species of bacteria were present, but generally only one predominated. The commercial strains used for smearing the cheese were recovered, but only in very small numbers early in ripening. Four species, B. aurantiacum, C. casei, C. variabile, and Staph. saprophyticus, were found on all batches of cheese, but their relative importance varied considerably. The results imply that significant variation occurs in the surface microflora of cheese.

Sources of the adventitious microflora of a smear-ripened cheese

AIMS

To determine the relationships between the major organisms from the cheese-making personnel and environment and the surface of a smear cheese.

METHODS AND RESULTS

360 yeast and 593 bacteria from the cheese surface, the dairy environment and the hands and arms of personnel were collected. Pulsed-field gel electrophoresis, repetitive sequence-based polymerase chain reaction and 16S rDNA sequencing were used for typing and identifying the bacteria, and mitochondrial DNA restriction fragment length polymorphism and Fourier-transform infrared spectroscopy for typing and identifying the yeast. The three most dominant bacteria were Corynebacterium casei, Corynebacterium variabile and Staphylococcus saprophyticus, which were divided into three, five and seven clusters, respectively, by macrorestriction analysis. The same clones from these organisms were isolated on the cheese surface, the dairy environment and the skin of the cheese personnel. Debaryomyces hansenii was the most dominant yeast.

CONCLUSIONS

A 'house' microflora exists in the cheese plant. Although the original source of the micro-organisms was not identified, the brines were an important source of S. saprophyticus and D. hansenii and, additionally, the arms and hands of the workers the sources of C. casei and C. variabile.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first time that the major contribution of the house microflora to the ripening of a smear-ripened cheese has been demonstrated.

Survival of surface ripening cultures during storage and monitoring their development on cheese

AIMS

To study the survival of bacteria isolated from the surface of smear cheese and monitor their development during cheese ripening.

METHODS AND RESULTS

The storage of five potential bacterial surface-ripening cheese cultures, Brevibacterium aurantiacum, Corynebacterium casei, Corynebacterium variable, Microbacterium gubbeenense and Staphylococcus saprophyticus, in maximum recovery diluent (MRD), containing 0.85% w/v or 5% w/v NaCl, at 21 or 4 degrees C for 40 days, was investigated. All five strains studied survived well with a maximum decrease of c. 2.5 log(10) CFU ml(-1) after storage for 40 days at 4 degrees C in 0.85% or 5% w/v NaCl. Survival, especially of C. variable, was less at 21 degrees C. The development of defined ripening cultures containing C. casei and Debaryomyces hansenii on two farmhouse cheeses was also evaluated. Using pulsed-field gel electrophoresis (PFGE) for the bacteria and mitochondrial DNA restriction fragment length polymorphism (mtDNA-RFLP) for the yeast, it was shown that the ripening cultures could be re-isolated in high numbers, 10(8) CFU cm(-2) for C. casei and 10(6) CFU cm(-2) for D. hansenii, from the cheese surface after 2.5 weeks of ripening.

CONCLUSIONS

Ripening strains of surface ripening cultures can be stored in MRD containing 5% w/v salt at 4 degrees C for at least 40 days. Such cultures are recovered in high numbers from the cheese during ripening.

SIGNIFICANCE AND IMPACT OF STUDY

This study has provided a low-cost and efficient way to store bacteria that could be used as ripening cultures for smear cheese. Such cultures can be recovered in high numbers from the cheese surface during ripening.

CD44 binds to the Shigella IpaB protein and participates in bacterial invasion of epithelial cells

Shigella entry into epithelial cells is characterized by a transient reorganization of the host cell cytoskeleton at the site of bacterial interaction with the cell membrane, which leads to bacterial engulfment in a macropinocytic process. Using affinity chromatography on HeLa cell extracts, we show here that the hyaluronan receptor CD44 associates with IpaB, a Shigella protein that is secreted upon cell contact. Overlay and solid-phase assays indicated that IpaB binds directly to the extracellular domain of CD44; binding is saturable and inhibitable, with a half-maximal inhibitory concentration of 175 nM. Immunoprecipitation experiments showed that IpaB associates with CD44 during Shigella entry. CD44 is recruited at bacterial entry sites and localizes at the plasma membrane of cellular extensions induced by Shigella. Pretreatment of cells with an anti-CD44 monoclonal antibody resulted in inhibition of Shigella-induced cytoskeletal reorganization, as well as inhibition of bacterial entry, whereas transfection of CD44 in cells that are deficient for CD44 results in increased bacterial binding to cells and internalization. The IpaB-CD44 interaction appears to be required for Shigella invasion by initiating the early steps of the entry process.

A functional role for ezrin during Shigella flexneri entry into epithelial cells

Shigella flexneri is an enteroinvasive bacterium responsible for bacillary dysentery in humans. Bacterial entry into epithelial cells is a crucial step for the establishment of the infection. It is characterized by a transient reorganization of the host cell cytoskeleton at the site of bacterial interaction with the cell membrane, which leads to bacterial engulfment by a macropinocytic process. We show in this study that the membrane-cytoskeleton linker, ezrin, a member of the ERM (ezrin, radixin, moesin) family, plays an active role in the process of Shigella uptake. Ezrin is highly enriched in cellular protrusions induced by the bacterium and is found in close association with the plasma membrane. In addition, Shigella entry is significantly reduced in cells transfected with a dominant negative allele of ezrin with entry foci showing much shorter cellular protrusions. These results indicate that ezrin not only acts as a membrane-cytoskeleton linker, but may also mediate extension of cellular projections in the presence of signals such as those elicited by invading microorganisms.

Rho family GTPases control entry of Shigella flexneri into epithelial cells but not intracellular motility

Shigella flexneri, an invasive bacterial pathogen, promotes formation of two cytoskeletal structures: the entry focus that mediates bacterial uptake into epithelial cells and the actin-comet tail that enables the bacteria to spread intracellularly. During the entry step, secretion of bacterial invasins causes a massive burst of subcortical actin polymerization leading the formation of localised membrane projections. Fusion of these membrane ruffles leads to bacterial internalization. Inside the cytoplasm, polar expression of the IcsA protein on the bacterial surface allows polymerization of actin filaments and their organization into an actin-comet tail leading to bacterial spread. The Rho family of small GTPases plays an essential role in the organization and regulation of cellular cytoskeletal structures (i.e. filopodia, lamellipodia, adherence plaques and intercellular junctions). We show here that induction of Shigella entry foci is controlled by the Cdc42, Rac and Rho GTPases, but not by RhoG. In contrast, actin-driven intracellular motility of Shigella does not require Rho GTPases. Therefore, Shigella appears to manipulate the epithelial cell cytoskeleton both by Rho GTPase-dependent and -independent processes.

Trafficking of Shigella lipopolysaccharide in polarized intestinal epithelial cells

Bacterial lipopolysaccharide (LPS) at the apical surface of polarized intestinal epithelial cells was previously shown to be transported from the apical to the basolateral pole of the epithelium (Beatty, W.L., and P.J. Sansonetti. 1997. Infect. Immun. 65:4395-4404). The present study was designed to elucidate the transcytotic pathway of LPS and to characterize the endocytic compartments involved in this process. Confocal and electron microscopic analyses revealed that LPS internalized at the apical surface became rapidly distributed within endosomal compartments accessible to basolaterally internalized transferrin. This compartment largely excluded fluid-phase markers added at either pole. Access to the basolateral side of the epithelium subsequent to trafficking to basolateral endosomes occurred via exocytosis into the paracellular space beneath the intercellular tight junctions. LPS appeared to exploit other endocytic routes with much of the internalized LPS recycled to the original apical membrane. In addition, analysis of LPS in association with markers of the endocytic network revealed that some LPS was sent to late endosomal and lysosomal compartments.

Alteration of HLA-B27 peptide presentation after infection of transfected murine L cells by Shigella flexneri

Shigella flexneri is a triggering agent for reactive arthritis in HLA-B27-susceptible individuals. Considering the intracellular multiplication of bacteria, it seems likely that bacterial peptides may be presented by the major histocompatibility complex (MHC) class I pathway. To examine this hypothesis, we infected HLA-B*2705- and/or human beta2-microglobulin-transfected murine L-cell lines with M90T, an invasive strain of S. flexneri. Bacterial infection induced no detectable modifications in the biosynthesis and expression level of HLA-B27, as assessed by immunoprecipitation, Northern blot analysis, and flow cytometry. Using confocal microscopy, we observed that bacterial infection induced a clustering of HLA-B27 molecules during macropinocytosis and before bacterial dissemination from cell to cell. Peptides naturally bound to HLA-B27 molecules were acid eluted from infected cells and separated by high-performance liquid chromatography. Major differences were observed in high-performance liquid chromatography profiles and in the nature of peptides presented following bacterial infection. Although most of the antigens presented were not accessed by Edman degradation, we obtained two sequences partially homologous to bacterial proteins. These peptides lacked the major HLA-B27 peptide anchor (Arg) at position 2, and one had an unusual length of 14 amino acids. These data suggest that alterations in the peptide presentation by HLA-B27 occur during infection, which could be relevant to the pathogenesis of HLA-B27-related arthritis.

Secretion of Shigella flexneri Ipa invasins on contact with epithelial cells and subsequent entry of the bacterium into cells are growth stage dependent

Upon contact with the surface of epithelial cells, Shigella flexneri secretes Ipa proteins through the Mxi-Spa type III secretion apparatus. Among the Ipa proteins, IpaB and IpaC form a soluble complex in the bacterial supernatant which appears to be sufficient to initiate the cellular rearrangements necessary to achieve bacterial entry. Here, we provide the first evidence that efficiency of bacterial entry into cells depends on the stage of bacterial growth. Bacteria in the early phase of exponential growth are six times more invasive than those in the stationary phase. The entry efficiency of the bacteria present on the cell surface appears to correlate with the percentage of those that are able to secrete their invasins. This suggests that the capacity to activate the Mxi-Spa apparatus is a major factor in the regulation of bacterial entry efficiency. Consistent with these observations, we have further shown that bacteria which have reached the stage of division secrete Ipa proteins more often than those that have not. Also, initial secretion occurs essentially in the area of the septation furrow. The Ipa proteins, secreted in the vicinity of the septation furrow, seem to initiate the early stages of reorganization of the host cell cytoskeleton.

Induction of adherence and degranulation of polymorphonuclear leukocytes: a new expression of the invasive phenotype of Shigella flexneri

In the present study, the ability of Shigella flexneri to activate polymorphonuclear neutrophils (PMN) was examined. The invasive serotype 5 strain M90T induced strong PMN adherence, which was dependent on both the multiplicity of infection and the duration of incubation. When tested under the same experimental conditions, the noninvasive strain BS176 (cured of the 220-kb virulence plasmid) was less efficient. Indeed, incubation of PMN for 2 h with either M90T or BS176 (multiplicity of infection, 100) induced 51.8% +/- 10.5% and 15.2% +/- 4.2% adherence, respectively (n = 3; P < 0.05). Stronger PMN activation by M90T was confirmed by evaluating PMN degranulation induced by the two strains. Whereas M90T triggered significant PMN secretion, BS176 did not. M90T strains with mutations in ipa genes were then analyzed. When PMN were incubated with these mutants, their activation was of the same intensity as that obtained with BS176. These data provide the first evidence for PMN activation induced by S. flexneri, a process which appears to be mediated by Ipa invasins.

MxiG, a membrane protein required for secretion of Shigella spp. Ipa invasins: involvement in entry into epithelial cells and in intercellular dissemination

Entry of Shigella flexneri into epithelial cells involves secretory proteins, the Ipa proteins, and their dedicated secretion apparatus, the Mxi-Spa translocon, which is encoded by the mxi and spa operons. We have characterized the mxiG gene that is located at the proximal part of the mxi operon. Inactivation of mxiG abolished lpa secretion, which indicates that MxiG is an essential component of the Mxi-Spa translocon. Immunoblotting analysis of membrane fractions suggests that the 42 kDa MxiG protein is associated with both the inner and outer membranes. Taking advantage of the complementation of the mxiG mutant by a plasmid carrying a wild-type copy of mxiG (which restored Ipa secretion, entry into HeLa cells, and cell-to-cell spread) we mutagenized the mxiG gene carried by the complementing plasmid to replace the RGD motif of MxiG by RAD. This mutation (mxiG*), which had no effect on the stability of the protein, did not affect Ipa secretion in vitro or entry into HeLa cells, but impaired intercellular dissemination. Therefore, MxiG and possibly proteins secreted by the Mxi-Spa translocation are involved not only in entry but also in spread of Shigella between epithelial cells.

Cadherin expression is required for the spread of Shigella flexneri between epithelial cells

Shigella flexneri, a gram-negative pathogen, invades the human colonic epithelium. After entering epithelial cells, bacteria escape into the cytoplasm, move intracellularly, and pass from cell to cell. The bacterium diverts actin and associated actin-binding proteins to generate a cytoskeleton-based motor that pushes forward the bacterium. As the moving bacterium reaches the inner face of the host-cell cytoplasmic membrane, a protrusion forms that allows passage of this bacterium into a neighboring cell. We show here that components of the intermediate junction are used by the bacterium to allow this passage. Using S180, a mouse fibroblastic sarcoma cell line that does not produce cell adhesion molecules (CAM), and S180L and S180cadN, the same cell line transfected with L-CAM and N-cadherin cDNA, respectively, we demonstrate that expression of a cadherin is required for cell-to-cell spread to occur.

Unipolar reorganization of F-actin layer at bacterial division and bundling of actin filaments by plastin correlate with movement of Shigella flexneri within HeLa cells

Shigella flexneri causes bacillary dysentery, an invasive disease of colonic epithelial cells in humans. The capacity of bacteria, once they have entered into a cell and escaped the phagocytic vacuole, to spread intracellularly and directly to adjacent cells without further extracellular passage is a key factor in invasion of the epithelial layer. Movement of intracellular bacteria is dependent upon the polymerization of actin; concentration of the formed filaments to one end of the bacterium is associated with initiation of movement. This movement may lead to the formation of a protrusion at the cell surface through which the bacterium passes to an adjacent cell. Development of these protrusions in infected HeLa cells is described, with emphasis on two critical observations. First, initiation of movement is coupled with bacterial division since elongation of the bacterial body is associated with relocalization of the previously uniformly distributed layer of actin to one pole of the bacterium. Second, the actin-bundling protein plastin appears to bundle the actin filaments just posterior to the bacterium, producing an ongoing contraction of the cylindrical actin tail that may be associated with forward movement of the bacterium within the protrusion.

icsB: a Shigella flexneri virulence gene necessary for the lysis of protrusions during intercellular spread

Shigella flexneri causes bacillary dysentery by invading epithelial cells of the colonic mucosa. We have characterized the icsB gene which is located on the virulence plasmid pWR100. After inactivation of icsB, the mutant strain remained invasive, but formed abnormally small plaques on HeLa cell monolayers, colonized only the peripheral cells of Caco-2 islets, and was unable to provoke a keratoconjunctivitis in guinea-pigs. Examination of infected HeLa cells showed that the icsB mutant was able to lyse the phagocytic vacuole and to form protrusions at the surface of infected cells, but, unlike the wild type, remained trapped in protrusions surrounded by two membranes. These results indicate that IcsB is involved in the lysis of the protrusions, a step necessary for intercellular spread.

IpaB of Shigella flexneri causes entry into epithelial cells and escape from the phagocytic vacuole

By creating mutations within the Shigella flexneri ipaB gene, we have demonstrated that the invasion of epithelial cells is a three-step process encompassing adhesion on the cell surface, entry and lysis of the phagocytic vacuole allowing subsequent access to the cytoplasm. SC403, an insertion mutant which lacks expression of IpaB but still expresses downstream genes, has been particularly studied. It is non-invasive, does not elicit actin polymerization, but binds to HeLa cells indicating that an adhesion step occurs immediately prior to the entry process. The consequence of the inactivation of ipaB on the intracellular behaviour of S.flexneri was investigated using the macrophage cell line J774. SC403 was unable to lyse the phagocytic vacuole; moreover, this strain did not display the contact mediated haemolytic activity characteristics of Shigella. In addition to being a major component of the invasion complex, IpaB acts as a membrane-lysing toxin enabling escape to the cytoplasmic compartment.

Movement along actin filaments of the perijunctional area and de novo polymerization of cellular actin are required for Shigella flexneri colonization of epithelial Caco-2 cell monolayers

Shigella flexneri invades eucaryotic cells and grows in the cytoplasm. Lysis of the phagosomal membrane is a prerequisite for both intracellular multiplication and movement of the bacteria that gain direct access to the host cell actin. In HeLa cells, bacteria generate their own movement essentially by inducing actin polymerization. Polymerization of actin enables them to move rapidly and randomly in the cytoplasm and to spread from one cell to another through protrusions of the host cell membrane. This movement was designated the Ics phenotype. In contrast, in chicken embryo fibroblasts, bacteria move along actin filaments in a very organized manner, following the cytoskeletal architecture; this movement was designated the Olm phenotype. Bacterial movement is a major virulence factor in that it is necessary for efficient colonization of the intestinal epithelium of infected macaque monkeys. Further characterization of the cellular events that lead to colonization of the colonic intestinal epithelium was needed. In order to characterize the movement in vitro in a cell assay system more closely related to the intestinal epithelium, we used human colonic epithelial Caco-2 cells. The movement of bacteria as observed by using immunofluorescence and confocal microscopy appeared to result from the expression of both the Olm and Ics phenotypes. The former allowed colonization of cells along the actin filament ring of the perijunctional area. The latter promoted passage from one cell to adjacent cells. This in vitro pattern of movement and multiplication gives S. flexneri, once it has entered an epithelial cell, the unique capacity to spread through the entire epithelial layer without having further contact with the extracellular compartment.

Shigella flexneri enters human colonic Caco-2 epithelial cells through the basolateral pole

The commonly accepted view that enteroinvasive bacteria enter cells of the intestinal epithelial lining through the apical surface can be challenged in the case of shigellosis. This study is based on in vitro experiments that showed that the invasion of human colonic Caco-2 cells by Shigella flexneri occurred through the basolateral pole of these cells. In these experiments, the few bacteria that interacted with the apical surface either bound to microvilli of the cell dome without causing detectable alteration or bound at the level of intercellular junctions at which they demonstrated a limited capacity for paracellular invasion, which permitted subsequent entry through the lateral domain of the cells. Treatment of Caco-2 cell monolayers with ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA), which disrupts intercellular junctions, greatly enhanced the rate of cell infection. These observations suggest a physiopathological paradox that may have important consequences for the understanding of the process of colonic invasion in vivo during shigellosis.

Stress fiber-based movement of Shigella flexneri within cells

icsA (virG), a gene located on pWR100, the virulence plasmid of Shigella flexneri serotype 5 (M90T), encodes a 120-kDa outer membrane protein. This protein promotes a random intracellular movement of the bacteria and leads to the infection of adjacent cells by the formation of protrusions. This movement, which involves the nucleation, polymerization, and subsequent polarization of actin, is referred to as the Ics phenotype (intra/intercellular spread). Here we present evidence that a second, distinct form of locomotion is also elaborated by S. flexneri in chicken embryo fibroblasts in which the Ics phenotype is not expressed. Using a combination of phase-contrast microcinematography and confocal microscopy, we have demonstrated that bacteria adopt parallel orientations by interacting with stress fibers. This interaction subsequently results in bacterial movement along the stress fibers themselves. This phenomenon occurs independently of the presence of a phagocytic vacuole which is lysed shortly after entry of the bacteria into the cell. It is expressed by M90T and SC560, its icsA mutant. This movement has been termed organelle-like movement (Olm phenotype) and is thought to account for the early accumulation of bacteria seen near the nucleus.

A nonvirulent mutant of Listeria monocytogenes does not move intracellularly but still induces polymerization of actin

Listeria monocytogenes has the capacity to penetrate and multiply within professional and nonprofessional phagocytic cells, such as the Caco-2 human enterocytelike cell line. It was shown recently that shortly after listeriae have been phagocytosed, the phagosomal membrane is dissolved, probably by the action of the bacterial cytolysin listeriolysin O. The listeriae, which are then lying obviously free in the cytoplasm, become surrounded by a coat of actin filaments within a few hours. Once formed, this layer of actin filaments is reorganized in an as yet unknown way to form polar tails, which seem to be associated to the generation of listerial movement inside the cytoplasm and in intercellular spread. By using transposon Tn916 mutagenesis, a bank of L. monocytogenes mutants was generated and subsequently screened by the plaque assay system in order to select an intracellular, nonmotile mutant of L. monocytogenes. One such mutant was identified. This mutant, called L. monocytogenes M117 Imt- (for intracellular motility), like the wild type, induced actin polymerization but was not able to rearrange the actin coat to generate movement and as a result remained entrapped within the actin cloud. In a mouse virulence assay, this strain was significantly reduced in virulence. L. monocytogenes M117 is the first example to date of a Listeria mutant which is still hemolytic and invasive but reduced in virulence.

Intracellular and cell-to-cell spread of Listeria monocytogenes involves interaction with F-actin in the enterocytelike cell line Caco-2

Listeria monocytogenes penetrates and multiplies within professional phagocytes and other cells such as the Caco-2 human enterocytelike cell line. Listeriolysin O, a membrane-damaging cytotoxin accounts for intracellular multiplication through lysis of the membrane-bound phagocytic vacuole. This work demonstrates that once released within the cytosol, L. monocytogenes acquires the capacity to spread intracellularly and infect adjacent cells by interacting with host cell microfilaments. Such evidence was obtained by using drugs which disrupt the cell cytoskeleton. Nocodazole, which blocks polymerization of microtubules, did not affect intracellular spread, whereas cytochalasin D, which blocks polymerization of G-actin, inhibited the intracellular motility of the bacteria. By using fluorescence staining with 7-nitrobenz-2-oxa-1,3-diazole-phallacidin (NBD-phallacidin), transmission electron microscopy, and immunogold labeling, direct evidence was obtained that intracellular bacteria were enveloped with a thick layer of F-actin. Within 2 h after entry, it was demonstrated by confocal microscopy that bacteria were following highly organized routes corresponding to stress fibers. Four hours after entry, some bacteria presented random movements which could be seen by the presence of a large trail of F-actin. Such movements also caused protrusions which deeply penetrated adjacent cells and resulted in the formation of vacuoles limited by a double membrane. After subsequent lysis of these membranes, bacteria released within the cytoplasm were able to multiply and invade new cells. In contrast, an hly::Tn1545 mutant of the wild-type microorganism demonstrated almost no intracellular spread. Only a few bacteria displaying delayed lysis of the phagocytic vacuole behaved like the wild-type strain. Hemolysin-mediated lysis of the phagocytic vacuole and subsequent interaction with host cell microfilaments may represent a major virulence factor allowing tissue colonization during listeriosis.

Immunodetection of lipopolysaccharide in macrophages during the processing of non invasive Shigella dysenteriae

The location of lipopolysaccharide (LPS) was studied by immunofluorescence and immunoelectron microscopy in macrophages infected with a non-invasive Shigella dysenteriae 1 strain. Bacterial degradation began only 3 h after the end of infection. The first visible sign of degradation was detected by immunogold labelling at the level of LPS which detached from the bacterial surface and was transferred to the perinuclear lysosomes. After a few hours, it was found in small vesicles spread over the whole macrophage cytoplasm in which it remained visible for 72 h. These vesicles seemed to belong to a compartment in which slowly or non-degradable compounds are stored. LPS separation from the bacterial surface was immediately followed by the degradation of the intrabacterial constituents. The long lag period observed before initiation of bacterial degradation was not due to a lack of phagosome acidification, since DAMP, a lysosomotropic drug was found in all phagosomes at the end of the ingestion period. The frequency of phagosome-lysosome fusion was 30% for S dysenteriae and 72% for B subtilis used as a reference of high fusion frequency. The low frequency of fusion of S dysenteriae may play an important role in the survival of the virulent strains in macrophage by providing bacteria enough time to lyse the phagosome membrane before lysosome fusion occurs.

Identification of icsA, a plasmid locus of Shigella flexneri that governs bacterial intra- and intercellular spread through interaction with F-actin

The capacity of Shigella to spread within the cytosol of infected epithelial cells and to infect adjacent cells is critical for the development of infection foci, which lead to mucosal abscesses. Shigella is a nonmotile microorganism that appears to utilize host cell microfilaments to generate intra- as well as intercellular movements, since this movement was inhibited by cytochalasin D and involvement of F-actin was demonstrated by direct labeling of infected cells with the specific dye N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)phallacidin. Such movements led to the formation of extracellular protrusions, which may explain cell to cell spread. icsA, a locus necessary for intra- and intercellular spread, was identified on the Shigella flexneri virulence plasmid pWR100. This locus was cloned and shown to express a 120-kDa outer membrane protein, which plays an important role in the interactions established between host cell microfilaments and the bacterial surface, thus leading to intracellular movement.

Mutation of Salmonella paratyphi A conferring cross-resistance to several groups of antibiotics by decreased permeability and loss of invasiveness

A spontaneous one-step mutant of Salmonella paratyphi A selected on ampicillin showed cross-resistance to all beta-lactam antibiotics except imipenem and to aminoglycosides, chloramphenicol, tetracycline, trimethoprim, and quinolones. It also grew as small colonies. Examination of the cell envelope of the mutant showed a quantitative decrease in three major outer membrane proteins of 40.6, 39.6 (presumably porins), and 24 kilodaltons and quantitative as well as qualitative modifications in the ladder pattern of lipopolysaccharide. Direct evidence for decreased permeability in the mutant included reduced uptake of [3H]glucose and norfloxacin, reduced accessibility of aztreonam and benzylpenicillin to penicillin-binding proteins in whole cells, and decreased diffusion of lactose and cephaloridine into proteoliposomes that were reconstituted with outer membrane proteins from the mutant. There was also loss of invasiveness of the mutant into HeLa cells. We assume that a pleiotropic mutation was responsible for multiple alterations in the outer membrane components of the resistant mutant of S. paratyphi A.

In vitro model of penetration and intracellular growth of Listeria monocytogenes in the human enterocyte-like cell line Caco-2

Penetration and replication of Listeria monocytogenes within intestinal epithelial cells were studied by infecting the human enterocyte-like cell line Caco-2. Entry was due to directed phagocytosis, as suggested by the inhibiting effect of cytochalasin D on bacterial entry and by electron microscopy showing bacteria inside membrane-limiting vacuoles at the early stage of infection. Only bacteria from pathogenic species (L. monocytogenes and Listeria ivanovii) were able to induce their own phagocytosis by Caco-2 cells, as opposed to Listeria seeligeri, Listeria welshimeri, and Listeria innocua. L. monocytogenes multiplied readily within Caco-2 cells, with an apparent generation time of about 90 min. Listeriolysin O was found to be a major factor promoting intracellular growth of L. monocytogenes. After being internalized at the same rate as that of its hemolytic revertant strain, a nonhemolytic mutant from L. monocytogenes failed to replicate significantly within Caco-2 cells. Electron microscopic study demonstrated that bacteria from the nonhemolytic mutant remained inside phagosomes during cellular infection, whereas hemolytic bacteria from L. monocytogenes were released free within the cytoplasm. This indicates that disruption of vacuole membranes by listeriolysin O-producing strains of L. monocytogenes might be a key mechanism allowing bacteria to escape from phagosomes and to multiply unrestricted within cell cytoplasm.

Evaluation with an iuc::Tn10 mutant of the role of aerobactin production in the virulence of Shigella flexneri

To evaluate the role of aerobactin production in the virulence of Shigella flexneri, a iuc::Tn10 insertion mutant was obtained from strain M90T, a serotype 5 isolate. This mutant was tested for its ability to invade and kill HeLa cells in monolayers, to elicit keratoconjunctivitis in guinea pigs and to infect ligated segments of rabbit ileal loops. Although this mutant did not grow in iron-depleted media, its ability to grow intracellulalry and eventually kill HeLa cells was unchanged from that of the wild-type strain. On the other hand, an inoculum-dependent effect was observed in the Sereny test, as well as in the rabbit ligated ileal loop model, which was monitored for fluid production and for both gross and microscopical alterations of the mucosa. Transduction of the mutation within a noninvasive plasmidless derivative of the parental strain did not alter growth within the intestinal lumen. We conclude that aerobactin production most probably provides invasive strains with a selective advantage for growth within tissues when located in extracellular compartments.

Metabolic events mediating early killing of host cells infected by Shigella flexneri

J774, a continuous macrophage cell-line, was infected by M90T, an invasive isolate of Shigella flexneri serotype 5 and BS176, its non invasive derivative--which does not harbor the 220 kbase virulence plasmid pWR100. Killing of host cells by intracellular M90T, commenced one hour after infection and was completed by 4 hours. Intracellular BS176 did not kill cells during the same period. Cell protein biosynthesis was totally inhibited by both strains within 2 hours of infection thus indicating that shiga-like toxin 1 (SLT1) could not account for early killing. On the other hand a sharp decrease in intracellular ATP was observed after 1 hour in cells infected with M90T. No significant increase in ATPase activity could be detected. A sharp increase in pyruvate production starting immediately after infection indicated impairement in mitochondrial respiration, which accounts for most ATP produced intracellularly. In addition, fermentation appeared to be totally blocked thus leaving no chance of the infected cells regenerating NAD. Concurrent increase in cAMP concentration within the first hour of infection may contribute to the rapid and efficient cell killing. Cells infected by BS176 always showed an intermediate phenotype (i.e. ATP depletion, pyruvate increase, lactate decrease). Early lysis of the phagocytic vacuole by M90T may account for this difference by allowing toxic products of the bacteria to diffuse more efficiently within the cytosol.