Biomedical subjects

K N Timmis

Publications and source records attributed to K N Timmis.

At least 73 records · Page 4Linked to original sources

PubMed1997

Stable expression of pertussis toxin in Bordetella bronchiseptica under the control of a tightly regulated promoter.

Pertussis toxin (PT) is an essential component of accellular vaccines against whooping cough. However, the industrial production of PT from Bordetella pertussis is impaired by slow growth and poor yields. To overcome these problems, we have constructed a minitransposon containing the tox operon under the control of a tightly regulated promoter responsive to an aromatic inducer. The expression cassettes have been integrated into the chromosome of Bordetella bronchiseptica 5376 and ATCC 10580 bvg. Five recombinant clones containing the tox operon under the control of the Psal promoter, which is activated by the product of nahR, were further characterized. The recombinant clones expressed PT after only 3 h of induction with sodium salicylate at levels similar to those of B. pertussis grown for 24 h. The stability of the engineered phenotype was 100% after 72 h of growth without selective pressure. The growth pattern was not modified either under noninducing conditions or in the presence of the inducer at low concentrations, suggesting that strain performance would not be affected in bioreactors when uncoupled from gene expression. Recombinant PT, which was localized mainly in the periplasm, was purified by affinity chromatography. The recombinant protein was immunologically indistinguishable from wild-type PT and retained its biological activity as determined by the CHO cell-clustering test. These recombinant clones appear to be useful tools for the cost-effective production of PT under conditions of improved biosafety, as demonstrated by the inducible expression of PT uncoupled from the bacterial biomass in a nonvirulent and fast-growing B. bronchiseptica background.

Animals↗

PubMed1997

Evidence that Formation of Protoanemonin from Metabolites of 4-Chlorobiphenyl Degradation Negatively Affects the Survival of 4-Chlorobiphenyl-Cometabolizing Microorganisms.

A rapid decline in cell viability of different PCB-metabolizing organisms was observed in soil microcosms amended with 4-chlorobiphenyl. The toxic effect could not be attributed to 4-chlorobiphenyl but was due to a compound formed from the transformation of 4-chlorobiphenyl by the natural microflora. Potential metabolites of 4-chlorobiphenyl, 4-chlorobenzoate and 4-chlorocatechol, caused similar toxic effects. We tested the hypothesis that the toxic effects are due to the formation of protoanemonin, a plant-derived antibiotic, which is toxic to microorganisms and which has been shown to be formed from 4-chlorocatechol by enzymes of the 3-oxoadipate pathway. Consistent with our hypothesis, addition to soil microcosms of strains able to reroute intermediary 4-chlorocatechol from the 3-oxoadipate pathway and into the meta-cleavage pathway or able to mineralize 4-chlorocatechol by a modified ortho-cleavage pathway resulted in reversal of this toxic effect. Surprisingly, while direct addition of protoanemonin influenced both the viability of fungi and the microbial activity of the soil microcosm, there was little effect on bacterial viability due to its rapid degradation. This rapid degradation accounts for our inability to detect this compound in soils amended with 4-chlorocatechol. However, significant accumulation of protoanemonin was observed by a mixed bacterial community enriched with benzoate or a mixture of benzoate and 4-methylbenzoate, providing the metabolic potential of the soil to form protoanemonin. The effects of soil heterogeneity and microcosm interactions are discussed in relation to the different effects of protoanemonin when applied as a shock load and when it is produced in small amounts from precursors over long periods.

Journal Article↗

PubMed1997

Metabolism of Chlorotoluenes by Burkholderia sp. Strain PS12 and Toluene Dioxygenase of Pseudomonas putida F1: Evidence for Monooxygenation by Toluene and Chlorobenzene Dioxygenases.

The degradation of toluene by Pseudomonas putida F1 and of chlorobenzenes by Burkholderia sp. strain PS12 is initiated by incorporation of dioxygen into the aromatic nucleus to form cis-dihydrodihydroxybenzenes. Toluene-grown cells of P. putida F1 and 3-chlorobenzoate-grown cells of Burkholderia sp. strain PS12 were found to monooxygenate the side chain of 2- and 3-chlorotoluene to the corresponding chlorobenzyl alcohols. Further metabolism of these products was slow, and the corresponding chlorobenzoates were usually observed as end products, whereas the 3-chlorobenzoate produced from 3-chlorotoluene in Burkholderia sp. strain PS12 was metabolized further. Escherichia coli cells containing the toluene dioxygenase genes from P. putida F1 oxidized 2- and 3-chlorotoluene to the corresponding chlorobenzyl alcohols as major products, demonstrating that this enzyme is responsible for the observed side chain monooxygenation. Two methyl- and chloro-substituted 1,2-dihydroxycyclohexadienes were formed as minor products from 2- and 3-chlorotoluene, whereas a chloro- and methyl-substituted cyclohexadiene was the only product formed from 4-chlorotoluene. The toluene dioxygenase of P. putida F1 and chlorobenzene dioxygenase from Burkholderia sp. strain PS12 are the first enzymes described that efficiently catalyze the oxidation of 2-chlorotoluene.

Journal Article↗

PubMed1997

Mineralization of 4-Chlorodibenzofuran by a Consortium Consisting of Sphingomonas sp. Strain RW1 and Burkholderia sp. Strain JWS.

The dibenzofuran-degrading bacterium Sphingomonas sp. strain RW1 (R.-M. Wittich, H. Wilkes, V. Sinnwell, W. Francke, and P. Fortnagel, Appl. Environ. Microbiol. 58:1005-1010, 1992) attacks 4-chlorodibenzofuran on the unsubstituted aromatic ring via distal dioxygenation adjacent to the ether bridge to produce 3(prm1)-chloro-2,2(prm1),3-trihydroxybiphenyl, which was identified by nuclear magnetic resonance spectroscopy and mass spectrometry. The compound is subsequently meta cleaved, and the respective intermediate is hydrolyzed to form a C-5 moiety, which is further degraded to Krebs cycle intermediates and to 3-chlorosalicylate. This dead-end product is released into the culture medium. A coculture of strain RW1 and the 3,5-dichlorosalicylate-degrading strain Burkholderia sp. strain JWS (A. Schindowski, R.-M. Wittich, and P. Fortnagel, FEMS Microbiol. Lett. 84:63-70, 1991) is able to completely degrade 4-chlorodibenzofuran with concomitant release of Cl(sup-) and formation of biomass.

Journal Article↗

PubMed1997

Construction and characterization of a live attenuated vaccine candidate against Shigella dysenteriae type 1.

Vaccine candidates against Shigella dysenteriae type 1, which is associated with the most severe cases of bacillary dysentery, were constructed. The rfp and rfb gene clusters, which code for S. dysenteriae 1 O antigen biosynthesis, were randomly integrated into either the chromosome or the virulence plasmid of the rough attenuated Shigella flexneri aroD strain SFL124-27 with a minitransposon carrying an arsenite resistance selection marker. The recombinant clones efficiently expressed the recombinant O antigen, exhibited a normal growth pattern, were able to invade and survive within eukaryotic cells to the same extent as the parental strain, and expressed the recombinant antigen within invaded cells. A clone was selected as the vaccine candidate, which was demonstrated to be immunogenic and safe in animal models, leading to 47% full protection and 53% partial protection against challenge with the wild-type strain.

Animals↗

PubMed1997

Metal selectivity of in situ microcolonies in biofilms of the Elbe river.

The ultrastructure of natural complex biofilm communities of the Elbe river grown in situ on microscopic glass coverslips was studied by using transmission electron microscopy and energy-dispersive x-ray (EDX) analysis. Characteristic microcolonies which measured between 3.3 and 9.3 microm in diameter were frequently observed. They had an outer envelope and harbored 6 to 30 cells. The cells formed short rods measuring 1.09 +/- 0.28 microm (n = 10) in length and 0.55 + 0.07 microm (n = 21) in width. They were surrounded by a thick layer of electron-transparent, nonosmicated matter, 120 to 300 nm thick. Individual cells exhibited a unique ultrastructural trait, namely, a concentric membrane stack which completely surrounded the cytoplasm. It consisted of three membrane doublets, which showed an overall thickness of 57 to 66 nm. The center-to-center spacing between two membrane doublets was 22.2 +/- 1.0 nm (n = 12). The bacterial cell wall seemed to be of the gram-negative type. The fact that upon shrinkage hexagonal clefts appeared proved the cells to be tightly packed, and septum formation by binary fissions was observed. All of these morphological details indicate that the cells within these microcolonies were actively growing and did not represent spore-like states. EDX analysis showed that only the electron-dense surface deposit of the microcolonies contained Mn and Fe in significant amounts, while these two elements were absent from the intercellular space and the cytoplasm of the microorganisms. In contrast, aluminum ions were able to penetrate the outer envelope of the microcolonies and were detected in the intercellular space. They were, however, completely absent from the microbial cytoplasm, indicating a filter cascade with respect to aluminum. From the ultrastructural data together with the deposition of iron and manganese on the microcolony surface, it appears that these organisms may belong to the genus Siderocapsa or Nitrosomonas. They do not precisely match any of the described species and may therefore represent a new species.

Biofilms↗

PubMed1997

Heterologous expression of biphenyl dioxygenase-encoding genes from a gram-positive broad-spectrum polychlorinated biphenyl degrader and characterization of chlorobiphenyl oxidation by the gene products.

The bphA1A2A3A4 gene cluster, encoding a biphenyl dioxygenase from Rhodococcus globerulus P6, a gram-positive microorganism able to degrade a wide spectrum of polychlorobiphenyls (PCBs), was expressed in Pseudomonas putida, thereby allowing characterization of chlorobiphenyl oxidation by this enzyme. While P6 biphenyl dioxygenase activity was observed in P. putida containing bphA1A2A3A4, no activity was detected in Escherichia coli cells containing the same gene cluster. In E. coli, transcription of genes bphB and bphCl, located downstream of bphA1A2A3A4, was shown to be driven solely by a vector promoter, which indicated that the lack of biphenyl dioxygenase activity was not due to a lack of mRNA synthesis. Radioactive labelling of bph gene products in E. coli implied inefficient translation of the bphA gene cluster or rapid degradation of the gene products. The biosynthesis of functional P6 biphenyl dioxygenase in P. putida cells containing the same plasmid construct that yielded no activity in E. coli emphasizes the importance of the host strain for heterologous expression and shows that synthesis, correct folding, and assembly of a Rhodococcus biphenyl dioxygenase can be achieved in a gram-negative organism. Dioxygenation of six mono- and dichlorinated PCB congeners by P. putida containing the P6 bphA gene cluster indicates the following ring substitution preference for this reaction (from most to least preferred): un-, meta-, para-, and ortho-substitution. No indications were found for dioxygenation of meta/para carbon pairs, or for hydroxylation of chlorinated carbons at any position of a monochlorinated ring, suggesting a strict specificity of this biphenyl dioxygenase for attack at nonhalogenated ortho/meta vicinal carbons. This contrasts the properties of an analogous enzyme from Pseudomonas sp. strain LB400, which can both dioxygenate at meta and para positions and dehalogenate substituted ortho carbons during ortho and meta dioxygenation.

Biodegradation, Environmental↗

PubMed1997

Influence of different rol gene products on the chain length of Shigella dysenteriae type 1 lipopolysaccharide O antigen expressed by Shigella flexneri carrier strains.

Introduction of the rol genes of Shigella dysenteriae 1 and Escherichia coli K-12 into Shigella flexneri carrier strains expressing the heterologous S. dysenteriae type 1 lipopolysaccharide resulted in the formation of longer chains of S. dysenteriae 1 O antigen. In bacteria producing both homologous and heterologous O antigen, this resulted in a reduction of the masking of heterologous O antigen by homologous lipopolysaccharide and an increased immune response induced by intraperitoneal immunization of mice by recombinant bacteria. The rol genes of S. dysenteriae 1 and E. coli K-12 were sequenced, and their gene products were compared with the S. flexneri Rol protein. The primary sequence of S. flexneri Rol differs from both E. coli K-12 and S. dysenteriae 1 Rol proteins only at positions 267 and 270, which suggests that this region may be responsible for the difference in biological activities.

Amino Acid Sequence↗

PubMed1997

Transcriptional control of the Pseudomonas TOL plasmid catabolic operons is achieved through an interplay of host factors and plasmid-encoded regulators.

The xyl genes of Pseudomonas putida TOL plasmid that specify catabolism of toluene and xylenes are organized in four transcriptional units: the upper-operon xylUWCAMBN for conversion of toluene/xylenes into benzoate/alkylbenzoates; the meta-operon xylXYZLTEGFJQKIH, which encodes the enzymes for further conversion of these compounds into Krebs cycle intermediates; and xylS and xylR, which are involved in transcriptional control. The XylS and XylR proteins are members of the XylS/AraC and NtrC families, respectively, of transcriptional regulators. The xylS gene is constitutively expressed at a low level from the Ps2 promoter. The XylS protein is activated by interaction with alkylbenzoates, and this active form stimulates transcription from Pm by sigma70- or sigmaS-containing RNA polymerase (the meta loop). The xylR gene is also expressed constitutively. The XylR protein, which in the absence of effectors binds in a nonactive form to target DNA sequences, is activated by aromatic hydrocarbons and ATP; it subsequently undergoes multimerization and structural changes that result in stimulation of transcription from Pu of the upper operon. This latter process is assisted by the IHF protein and mediated by sigma54-containing RNA polymerase. Once activated, the XylR protein also stimulates transcription from the Ps1 promoter of xylS without interfering with expression from Ps2. This process is assisted by the HU protein and is mediated by sigma54-containing RNA polymerase. As a consequence of hyperexpression of the xylS gene, the XylS protein is hyperproduced and stimulates transcription from Pm even in the absence of effectors (the cascade loop). The two sigma54-dependent promoters are additionally subject to global (catabolite repression) control.

Bacterial Proteins↗

PubMed1996

Muconolactone isomerase of the 3-oxoadipate pathway catalyzes dechlorination of 5-chloro-substituted muconolactones.

An enzyme of Alcaligenes eutrophus JMP 134 which catalyzes dechlorination of (4R, 5R)- and (4R,5S)-5-chloro-3-methyl- and (4R, 5S)-5-chloromuconolactone of principally 3-methyl-trans-, 3-methyl-cis-dienelactone and cis-dienelactone, respectively, was purified to homogeneity. The enzyme was identified as muconolactone isomerase on the basis of its high activity with muconolactone and on its high degree of sequence similarity with previously described muconolactone isomerases. Molecular mass determinations of the highly hydrophobic and heat-resistant enzyme indicated a decameric structure involving a single 10.100-kDa subunit similar to that of muconolactone isomerase of Pseudomonas putida. Kinetic analysis showed cooperative effects between the subunits during conversion of (4R, 5S)-5-chloro-3 -methylmuconolactone. (4R, 5S)-5-chloromuconolactone was the preferred substrate, over the natural substrate (4S)-muconolactone. The (4S, 5S)-structure was found to be an inhibitor of (4R, 5R)-5-chloro-3-methylmuconolactone transformation. Methylsubstitution of the substrate results in a higher affinity for the enzyme, but a drastically lower velocity, resulting in a lower specificity constant.

4-Butyrolactone↗

PubMed1996

Construction of recombinant aroA salmonellae stably producing the Shigella dysenteriae serotype 1 O-antigen and structural characterization of the Salmonella/Shigella hybrid LPS.

The TN501 mercury resistant transposon containing the rfp and rfb loci encoding biosynthesis of the O-antigen of Shigella dysenteriae serotype 1 lipopolysaccharide (LPS) was constructed and introduced into aroA mutants of Salmonella typhimurium and Salmonella dublin. In five recombinant strains, both homologous LPS and hybrid LPS, consisting of Salmonella lipid A-core and Shigella O-antigen, were produced. All derivatives but one (SL3235) stably inherited the new trait. Immunofluorescence microscopy, using mixtures of differentially-labelled antibodies specific for either the Salmonella or the Shigella O-antigen, demonstrated that individual bacteria produced both types of LPS. Qualitative and quantitative analysis of polysaccharides obtained by mild hydrolysis of purified LPS was carried out by methylation analysis and NMR spectroscopy, and revealed that the ratio of Salmonella to Shigella O-antigen repeating units in the high molecular weight fraction of isolated polysaccharides varied from 1.3: 1 to 8.4:1 as based on the relative proportions of 1,4,5-tri-O-acetyl-2,3-di-O-methyl-L- rhamnitol (Salmonella repeating unit) and 1,3,5-tri-O-acetyl-2,4-di-O-methyl-L-rhamnitol (Shigella repeating unit). The attachment site of the Shigella O-antigen to the Salmonella core was investigated by construction of a mutant rfp-rfb gene cluster encoding the synthesis of only one repeat unit of the Shigella dysenteriae type 1 O-antigen, and its introduction into a rough Salmonella strain. This hybrid organism produced a polysaccharide with the following structure, [formula: see text] demonstrating that the Shigella dysenteriae type 1 O-antigen is linked at position O-4 of the subterminal D-glucose unit in the Salmonella core.

3-Phosphoshikimate 1-Carboxyvinyltransferase↗

PubMed1996

Towards a vaccine candidate against Shigella dysenteriae 1: expression of the Shiga toxin B-subunit in an attenuated Shigella flexneri aroD carrier strain.

Shiga toxin is considered to be one of the main causes of severe side effects, such as the hemolytic uremic syndrome, of shigellosis. The genetic determinants for a fusion of its B-subunit (StxB), which mediates toxin binding to target cells, with the COOH-terminus of Escherichia coli hemolysin A (Stx'-'HlyA) has been combined with the determinants of the accessory translocator proteins HlyB and HlyD in a Notl cassette. This cassette has been integrated via a mini-transposon into a recombinant vaccine strain that expresses Shigella flexneri Y and Shigella dysenteriae 1 O-antigen lipopolysaccharides. Characterisation of the resulting strains showed that they maintain all the vaccine-relevant biological properties of the carrier and export efficiently the StxB'-'Hly A fusion peptide into the culture medium. Polyclonal antibodies raised against the StxB'-'HlyA fusion exhibited neutralizing activity in the HeLa cytotoxicity assay. The newly developed strains thus represent promising bivalent vaccine candidates against severe shigellosis caused by S. dysenteriae 1 and S. flexneri Y.

Antigens, Bacterial↗

PubMed1996

Restricting the dispersal of recombinant DNA: design of a contained biological catalyst.

To restrict horizontal gene spread and, thus, create organisms whose behavior in the field is more predictable, we have combined a mini-Tn5 cloning system that allows stable insertion of foreign genes into the chromosomes of a variety of Gram-negative bacteria with a gene-containment circuit based on the universal lethal-function colicin E3. Use of the system is exemplified by the construction of a micro-organism designed to degrade polychlorinated biphenyls, important environmental pollutants. The relevant genotype of the microorganism is subject to a stringent gene-containment mechanism that provides neither an advantage nor a disadvantage to the host cell for survival, but decreases frequencies of productive chromosomal transfer frequencies by at least four orders of magnitude.

Catalysis↗

PubMed1996

An Escherichia coli hemolysin transport system-based vector for the export of polypeptides: export of Shiga-like toxin IIeB subunit by Salmonella typhimurium aroA.

The export of Escherichia coli hemolysin across the cytoplasmic and the outer membranes requires the COOH-terminal signal sequence of HlyA, the two specific translocator proteins HlyB and HlyD, and the outer membrane protein TolC. We have developed an export cloning system that is composed of two vectors: one in which the fusion of the desired gene with the 3'-end of hlyA is generated, and a second in which the sequences containing the fusion are combined with the accessory genes hlyB and hlyD, thereby reconstructing the natural organization of the hly locus. In the second vector the fusion and the accessory genes are flanked by Notl sites, allowing subcloning of the whole cluster into a variety of minitransposons to achieve the stable integration of the constructs into the chromosome of Gram-negative bacteria. Since some applications may require the production of transcriptional fusions, an alternative version of the system provides the efficient translation initiation region of T7 phage gene 10 upstream of the fusion protein coding sequence. The usefulness of the system was assessed by constructing a fusion between the gene encoding the B subunit of Shiga-like toxin lle and the 3'-end of hlyA. An attenuated Salmonella typhimurium vaccine strain harboring the resulting construct, either in multicopy or monocopy, efficiently expressed and exported the chimeric protein. We anticipate that this system will lead to a higher stability of the engineered function and permit a faithful monitoring of the export of the recombinant peptide under physiologic single-copy conditions.

3-Phosphoshikimate 1-Carboxyvinyltransferase↗

PubMed1996

System to study horizontal gene exchange among microorganisms without cultivation of recipients.

Ribosomal RNA genes are characterized by highly conserved sequences and are present in multiple copies in most prokaryotic chromosomes. In principle, therefore, they might serve as sites for homologous recombination between unrelated microorganisms. Plasmids containing 23S ribosomal gene sequences, from different bacteria, which had been interrupted by insertion of a kanamycin-resistance gene, were used to transform Acinetobacter sp. DSM587 (former name: Acinetobacter calcoaceticus BD413-ivl10). In all cases, homologies between the 23S rRNA genes of phylogenetically distant bacteria and Acinetobacter sp. DSM587 were sufficient for replacement recombination events. The integration events, resulting in inactivation of any one of the seven rrn operons of Acinetobacter sp. DSM587, had no observable influence on cell growth. These results suggest the possibility of rRNA genes serving as natural vehicles for horizontal gene transfer. They also provide the basis of a novel strategy to analyse gene transfer without selection or cultivation of recipient cells. Because of the highly conserved structure of bacterial rrn operons, recombination events subsequent to gene transfer can be readily identified by polymerase chain reaction amplification of the recombinant sequence using a universal forward primer for the 16S rRNA gene and a reverse primer specific for the integrated marker gene.

Acinetobacter↗

PubMed1996

The two-step lysis system of pneumococcal bacteriophage EJ-1 is functional in gram-negative bacteria: triggering of the major pneumococcal autolysin in Escherichia coli.

The holin function Ejh of the pneumococcal bacteriophage EJ-1 has been characterized. It shows structural features similar to, and functionally complemented, the prototype member of the holin family. In Escherichia coli and Pseudomonas putida the Ejh product caused cellular death, and changes in cell morphology could be accounted for by lesions in the cytoplasmic membrane. Expression of ejh resulted in the inhibition of growth in a variety of phylogenetically distant bacterial genera, suggesting a broad spectrum of action. Concomitant expression of the ejh and ejl (encodes a lysin) genes led to lysis of E. coli and P. putida cells. Remarkably, the Ejl lysin was able to attack murein from bacteria lacking choline in their sacculi, which suggests that pneumococcal lysins have a broader substrate specificity than previously assumed. Furthermore, the Ejh holin was able to trigger activity of the major pneumococcal autolysin cloned and expressed in E. coli, and this raised new questions about the regulation of this model autolysin. A new function for holins in systems where the phage lysin is supposed to be associated with the membrane is proposed.

Amino Acid Sequence↗

PubMed1996

A stringently controlled expression system for analysing lateral gene transfer between bacteria.

The lateral transfer of genetic information among microorganisms is a major force driving the outstanding adaptability of microbial communities to environmental changes. Until now little information has been obtained on gene transfer in natural ecosystems. We present here a genetic circuit for detecting and quantifying horizontal gene transfer from a defined donor microorganism to recipient organisms in the absence of selection for a recipient-specific phenotype. The system consists of an engineered lacZ (encoding beta-galactosidase) reporter gene whose expression is controlled by a synthetic regulatory element based on a fusion between the Pr promoter-operator from lambda bacteriophage and the 5' non-coding leader region of the inp gene encoding the IS 10 transposase function. Expression of this reporter cassette in the recombinant microorganism is completely shut down by two chromosomally encoded trans-acting repressors working at the level of transcription (the Cl-EK117 protein from the lambda phage), and at the level of translation (the antisense RNA-OUT of the IS 10 element). When the reporter element is transferred to a different host by any mechanism, it escapes repression and becomes expressed. The system was validated with Pseudo-monas putida, and conjugational transfer frequencies of the reporter element as low as 10(-6) were detected. The modular design and broad host range of the genetic circuit, in combination with biomarkers which permit real-time in situ detection, will facilitate the monitor-ing of gene flow in a non-disruptive manner within the environment.

Bacteria↗

PubMed1996

Apoptosis of mouse dendritic cells is triggered by listeriolysin, the major virulence determinant of Listeria monocytogenes.

Infection of a murine-spleen dendritic cell line by Listeria monocytogenes was found to induce cell death through apoptosis. To characterize the bacterial product(s) involved in induction of apoptosis, dendritic cells were infected with the L. monocytogenes EGD strain and several isogenic mutants deficient in the production of individual listerial virulence factors. The ability to induce cellular apoptosis was retained by all mutants tested, except the prfA and delta hly mutants, both of which are unable to produce listeriolysin. Apoptosis was also induced by purified listeriolysin suggesting that this protein directly induces apoptosis. Purified recombinant listeriolysins rendered either weakly haemolytic by a C-484 to S mutation, or nonhaemolytic by a W-491 to A mutation exhibited little or no capacity to induce apoptosis, indicating that both activities are associated within the same protein region. Treatment with purified listeriolysin or L. monocytogenes infection also triggers apoptosis in explanted bone-marrow dendritic cells. Thus invasion of dendritic cells by L. monocytogenes, which results in cell death, may play an important role in the pathogenesis of listerial infections by impairing immune responses, hindering bacterial clearance and promoting spread of the infection.

Animals↗