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PubMed2006

Subversion of cellular functions by Listeria monocytogenes.

Listeria monocytogenes is a Gram-positive bacterium that is able to invade and multiply within eukaryotic cells. Its intracellular life-cycle includes pathogen-induced phagocytosis, lysis of the phagocytic vacuole, movement in the cytoplasmic environment, and a cell-to-cell spread mechanism. Many L. monocytogenes virulence factors have been studied in detail, certain of which subvert specific eukaryotic cell functions in order to favour infection. During entry, the invasion protein InlA takes advantage of the adhesion molecule E-cadherin and the adherens junction machinery to adhere to target and invade polarized epithelial cells. Another invasion protein of the internalin family, InlB, subverts the signalling pathway of the hepatocyte growth factor receptor Met to induce endocytosis of the receptor and also to favour internalization of the bacteria in non-polarized epithelial cells. Once inside the cell, the haemolysin of L. monocytogenes--the listeriolysin O or LLO--is secreted to lyse the phagocytic vacuole, and when the bacteria is freed in the cytoplasm, the activity of the LLO is in part regulated by the infected cell itself, taking advantage of the pH sensitivity of the LLO that leads to its inactivation in the neutral eukaryotic cell cytoplasm. Finally, to induce bacterial movement in the cytoplasm, the L. monocytogenes surface protein ActA mimics the activity of the eukaryotic WASP family of proteins to recruit to the bacteria the actin nucleation machinery required for actin polymerization and for the formation of the actin structures (called 'actin comet tails') that propel the parasite in the cytosol and help it to invade neighbouring cells.

Bacterial Proteins↗

PubMed2006

A truncated Bacillus subtilis dal gene with a 3' ssrA gene tag regulates the growth and virulence of racemase-deficient Listeria monocytogenes.

Listeria monocytogenes (Lm) is a Gram-positive intracellular pathogen that can elicit strong cellular immunity. An attenuated strain (Lmdd) with deletions in two genes (dal and dat) required for d-alanine synthesis and viability has been shown to induce long-lived protective systemic and mucosal immune responses in mice when administered in the presence of the required amino acid. To bypass the necessity for exogenous d-alanine without compromising the safety of the original strain, the defect of Lmdd was complemented with a heterologous Bacillus subtilis dal gene, and the effects of truncating the upstream region of the gene on its transcription efficiency and of modifying its protein product with an ssrA tag at the 3'-terminus were examined. The strains with 551 bp and 80 bp upstream regions showed high levels of transcription and grew without d-alanine. The strains with the shortest upstream regions, 48 bp and 18 bp, showed greatly decreased levels of transcription and failed to grow in the absence of d-alanine. Addition of an ssrA tag to the longer genes resulted in a somewhat altered growth pattern in media and a reduced plaque size on L2 fibroblasts. These bacteria contained low levels of racemase protein and reduced free pools of d-alanine. One of the strains tested further, Lmdd/pA80S, was rapidly cleared from the spleens of infected mice but nevertheless induced a strong immune response that protected mice against challenge by wild-type L. monocytogenes. These bacteria can thus induce immune responses in mice comparable to the original Lmdd strain, but without the need for exogenous d-alanine, and may have use as a live vaccine vector against infectious diseases and cancers.

Alanine↗

PubMed1993

Identification of a phosphoenolpyruvate:fructose phosphotransferase system (fructose-1-phosphate forming) in Listeria monocytogenes.

Listeria monocytogenes is a gram-positive bacterium whose carbohydrate metabolic pathways are poorly understood. We provide evidence for an inducible phosphoenolpyruvate (PEP):fructose phosphotransferase system (PTS) in this pathogen. The system consists of enzyme I, HPr, and a fructose-specific enzyme II complex which generates fructose-1-phosphate as the cytoplasmic product of the PTS-catalyzed vectorial phosphorylation reaction. Fructose-1-phosphate kinase then converts the product of the PTS reaction to fructose-1,6-bisphosphate. HPr was shown to be phosphorylated by [32P]PEP and enzyme I as well as by [32P]ATP and a fructose-1,6-bisphosphate-activated HPr kinase like those found in other gram-positive bacteria. Enzyme I, HPr, and the enzyme II complex of the Listeria PTS exhibit enzymatic cross-reactivity with PTS enzyme constituents from Bacillus subtilis and Staphylococcus aureus.

Bacterial Proteins↗

PubMed2006

Iron acquisition systems for ferric hydroxamates, haemin and haemoglobin in Listeria monocytogenes.

Listeria monocytogenes is a Gram-positive bacterium that causes severe opportunistic infections in humans and animals. We biochemically characterized, for the first time, the iron uptake processes of this facultative intracellular pathogen, and identified the genetic loci encoding two of its membrane iron transporters. Strain EGD-e used iron complexes of hydroxamates (ferrichrome and ferrichrome A, ferrioxamine B), catecholates (ferric enterobactin, ferric corynebactin) and eukaryotic binding proteins (transferrin, lactoferrin, ferritin, haemoglobin). Quantitative determinations showed 10-100-fold lower affinity for ferric siderophores (Km approximately 1-10 nM) than Gram-negative bacteria, and generally lower uptake rates. Vmax for [59Fe]-enterobactin (0.15 pMol per 10(9) cells per minute) was 400-fold lower than that of Escherichia coli. For [59Fe]-corynebactin, Vmax was also low (1.2 pMol per 10(9) cells per minute), but EGD-e transported [59Fe]-apoferrichrome similarly to E. coli (Vmax=24 pMol per 10(9) cells per minute). L. monocytogenes encodes potential Fur-regulated iron transporters at 2.031 Mb (the fur-fhu region), 2.184 Mb (the feo region), 2.27 Mb (the srtB region) and 2.499 Mb (designated hupDGC region). Chromosomal deletions in the fur-fhu and hupDGC regions diminished iron uptake from ferric hydroxamates and haemin/haemoglobin respectively. In the former locus, deletion of fhuD (lmo1959) or fhuC (lmo1960) strongly reduced [59Fe]-apoferrichrome uptake. Deletion of hupC (lmo2429) eliminated the uptake of haemin and haemoglobin, and decreased the virulence of L. monocytogenes 50-fold in mice. Elimination of srtB region genes (Deltalmo2185, Deltalmo2186, Deltalmo2183), both sortase structural genes (DeltasrtB, DeltasrtA, DeltasrtAB), fur and feoB did not impair iron transport. However, deletion of bacterioferritin (Deltafri, lmo943; 0.97 Mb) decreased growth and altered iron uptake: Vmax of [59Fe]-corynebactin transport tripled in this strain, whereas that of [59Fe]-apoferrichrome decreased 20-fold.

Amino Acid Sequence↗

PubMedDate not supplied

Symposium on microbiology update: old friends and new enemies. Listeria monocytogenes.

Listeria monocytogenes, one of the "new enemies" in food microbiology, is a human and animal pathogen that is widespread in nature. The organism is a transient constituent of the intestinal flora excreted by 1-10% of healthy humans. It is an extremely hardy organism and can survive for many years in the cold in naturally infected sources. L. monocytogenes has been isolated from a wide variety of foods, including dairy products, meats, and fish. Although most of the foodborne listeriosis outbreaks have been linked to the consumption of dairy products, recent sporadic cases have been associated with meats, as well as other foods. It is now recognized that listeriolysin 0, a 60-kilodalton protein, is one of the major virulence factors of the organism. All strains of L. monocytogenes are pathogenic by definition although some appear to be more virulent than others. There have been recent reports of hemolytic isolates of L. monocytogenes, which are nonpathogenic for mice. Attachment to and penetration of cells also appear to be prerequisites for human infection. Cultural methodology for isolating the organism from foods has been in a state of flux since 1985. Rapid methods using both ELISA and DNA technology have been developed. Because of the widespread nature of the organism, it is nearly impossible to eliminate it from the food supply. However, by using a hazard analysis-critical control point approach, the health hazard associated with this organism can be reduced to a minimum.

Food Microbiology↗

PubMed2005

Translation elongation factor EF-Tu is a target for Stp, a serine-threonine phosphatase involved in virulence of Listeria monocytogenes.

Listeria monocytogenes is a pathogen that causes listeriosis, a severe food-borne infection. This bacterium, in order to survive and grow in the multiple conditions encountered in the host and the environment, has evolved a large number of regulatory elements, in particular many signal transduction systems based on reversible phosphorylation. The genome sequence has revealed genes for 16 putative two-component systems, four putative tyrosine phosphatases, three putative serine-threonine kinases and two putative serine-threonine phosphatases. We found that one of the latter genes, stp, encodes a functional Mn(2+)-dependent serine-threonine phosphatase similar to PPM eukaryotic phosphatases (Mg(2+)-or Mn(2+)-dependent protein phosphatase) and is required for growth of L. monocytogenes in a murine model of infection. We identified as the first target for Stp, the elongation factor EF-Tu. Post-translational phosphorylation of EF-Tu had been shown to prevent its binding to amino-acylated transfer RNA as well as to kirromycin, an antibiotic known to inhibit EF-Tu function. Accordingly, an stp deletion mutant is less sensitive to kirromycin. These results suggest an important role for Stp in regulating EF-Tu and controlling bacterial survival in the infected host.

Listeria monocytogenes↗

PubMed2001

Can food-related environmental factors induce different behaviour in two key serovars, 4b and 1/2a, of Listeria monocytogenes?

Listeria monocytogenes isolates (81 in total; 42 isolated from cases of human listeriosis: 39 isolated from food), belonging to serovars 1/2a or 4b, were studied for any group differences between serovars to selected factors associated with foods (two bacteriocins and mild heat treatment), growth kinetics at 37 degrees C and pathogenicity for chick embryos. The isolates were tested for sensitivity to two bacteriocins at 4 degrees C and 37 degrees C, and were tested for the remaining parameters both before and after exposure to cold storage (4 degrees C) with starvation. In addition, the isolates were typed using pulsed field gel electrophoresis (PFGE), multilocus enzyme electrophoresis (MEE) and phage typing to find any correlation between the types and group differences in the chosen parameters. Considerable strain diversity within each L. monocytogenes serovar with respect to the chosen parameters was observed, especially after exposure to cold storage. Nevertheless, the serovar 1/2a isolates, as a group, tended to be more resistant to the two antilisterial bacteriocins at 4 degrees C than the group of serovar 4b isolates. In contrast, after cold storage at 4 degrees C, L. monocytogenes serovar 4b isolates, as a group, tended to be more resistant to heat treatment at 60 degrees C than the group of 1/2a isolates. In addition, the serovar 4b group tended to have shorter lag phases and higher pathogenicity, when transferred from cold storage to body temperature (37 degrees C), than the group of serovar 1/2a isolates. No correlation between PFGE-, MEE- and phage-types and the tested parameters was found. Although the above serovar-related differences were observed only when mean values of the groups were compared (not all isolates within each group followed the group pattern), the results indicate interesting directions for further research.

Animals↗

PubMed1978

Light and electron microscopic study of the livers of pregnant mice infected with Listeria monocytogenes.

Listeria monocytogenes cells were observed in the hepatic cell cytoplasm or in the phagosome at 24 and 48 hours but not at 72 hours after inoculation in pregnant mice. The presence of bacteria initially in a membrane-bound vesicle indicates that the bacteria enter the hepatic cells by endocytosis, resulting in eventual destruction of hepatic cells. Characteristic lesions of the liver at 24 and 48 hours after inoculation consist of multiple focal areas of necrosis. The initial neutrophilic reaction seems to give way to a mononuclear reaction (listeriomas) at 72 hours after inoculation. Dilation of rough endoplasmic reticulum and release of many of the bound ribosomes with a relative increase in the number of free ribosomes was observed. Hepatic lesions were not observed in control (nonpregnant) mice.

Animals↗

PubMed1991

Precise prediction of a dominant class I MHC-restricted epitope of Listeria monocytogenes.

Listeria monocytogenes is a Gram-positive bacterium which grows in the cytoplasm of eukaryotic cells and can cause severe disease in immunocompromised individuals. In murine systems CD8+ T lymphocytes have been shown to be important effectors of acquired protective immunity against L. monocytogenes. Class I MHC-restricted CD8+ cytotoxic T lymphocytes (CTL), which lyse J774 macrophage-like targets infected with L. monocytogenes, are induced following in vivo injection of live organisms. Natural peptide epitopes derived from L. monocytogenes can be acid-extracted from heavily infected BALB/c spleens and detected by CTL. A CTL clone, B9, derived from a (BALB/c x C57BL/6)F1 (H-2dxb) mouse, recognizes one of these natural epitopes in an H-2Kd-restricted fashion. B9 also recognizes P815 (H-2d) mastocytoma cells transfected with the listeriolysin gene. To identify the region of the listeriolysin recognized by CTL we used the H-2Kd peptide-binding motif described by Rammensee and colleagues to synthesize 11 nonamer peptides. One of these peptides, listeriolysin 91-99, was recognized very efficiently by B9. This represents the first identified class I MHC-restricted epitope of bacteria and demonstrates the utility of the allele-specific motif for predicting CTL epitopes.

Amino Acid Sequence↗

PubMed1992

Host cell actin assembly is necessary and likely to provide the propulsive force for intracellular movement of Listeria monocytogenes.

Listeria monocytogenes is able to escape from the phagolysosome and grow within the host cell cytoplasm. By 3 h after initiation of infection, actin filaments begin to concentrate at one end of the bacterium. Polarization of F-actin is associated with intracellular bacterial movement, long projections of actin filaments forming directly behind the moving bacteria. New actin monomers are added to the region of the projection in proximity to the bacterium. The rate of new actin filament growth correlates closely with the speed of bacterial migration. This actin structure is anchored within the cytoplasm, serving as a fixed platform for directional expansion of the actin filament network. The actin projection progressively lengthens as the bacterium migrates. Cytochalasin blocks both elongation of the projection and bacterial movement but does not result in complete depolymerization of the bacterially induced actin structure, residual actin and alpha-actinin persisting in proximity to one end of the bacterium. Bacteria initially migrate within the cortical cytoplasm but later move to the peripheral membrane, where they form filopodiumlike structures which pivot and undulate in the extracellular medium. In the filopodia, bacteria are occasionally seen to abruptly change direction, turn 180 degrees, and move back into the medullary region of the host cell. All filopodium movement ceases once the bacterium containing the F-actin projection returns to the cortical cytoplasm. These results indicate that host cell actin polymerization is necessary for intracellular migration of listeriae and suggest that directional actin assembly may in fact generate the propulsive force for bacterial and filopodial movement.

Actins↗

PubMed2006

Exploring the role of the CTL epitope region of listeriolysin O in the pathogenesis of Listeria monocytogenes.

Listeria monocytogenes is a facultative intracellular bacterial pathogen responsible for severe opportunistic infections in humans and animals. The secreted cholesterol-dependent cytolysin, listeriolysin O (LLO), mediates phagosomal escape and allows bacterial growth in the cytosol of infected cells. In order to identify new LLO determinants participating in bacterial pathogenesis, this study focused on a major target of LLO proteolytic cleavage in vitro, the CTL epitope region (residues 91-99). Mutations were generated by site-directed mutagenesis in the epitope or in the two clusters of positive charges flanking the epitope. Two LLO mutants (a single mutation K103A and a double mutation R89G, K90G) were normally and stably secreted by L. monocytogenes. In contrast, a mutant carrying four amino acid substitutions in the epitope itself (Y92K, D94A, E97K, Y98F) was highly susceptible to proteolytic degradation. While these three LLO mutant proteins showed a reduced haemolytic activity, they all promoted efficient phagosomal escape and intracellular multiplication in different cell types, and were non-cytotoxic. The deletion of the epitope (Delta91-99), as well as the substitution of two, three or four of the four lysine residues (K103 to K106) by alanine residues did not lead to the production of a detectable protein. These results confirm the lack of correlation between haemolytic activity and phagosomal membrane disruption. They reveal the importance of the 91-99 region in the production of a stable and functional LLO. LD(50) determinations in the mouse model suggest a possible link between LLO stability and virulence.

Amino Acid Sequence↗

PubMed2006

A single-nucleotide-polymorphism-based multilocus genotyping assay for subtyping lineage I isolates of Listeria monocytogenes.

Listeria monocytogenes is a facultative intracellular pathogen responsible for food-borne disease with high mortality rates in humans and is the leading microbiological cause of food recalls. Lineage I isolates of L. monocytogenes are a particular public health concern because they are responsible for most sporadic cases of listeriosis and the vast majority of epidemic outbreaks. Rapid, reproducible, and sensitive methods for differentiating pathogens below the species level are required for effective pathogen control programs, and the CDC PulseNet Task Force has called for the development and validation of DNA sequence-based methods for subtyping food-borne pathogens. Therefore, we developed a multilocus genotyping (MLGT) assay for L. monocytogenes lineage I isolates based on nucleotide variation identified by sequencing 23,251 bp of DNA from 22 genes distributed across seven genomic regions in 65 L. monocytogenes isolates. This single-well assay of 60 allele-specific probes captured 100% of the haplotype information contained in approximately 1.5 Mb of comparative DNA sequence and was used to reproducibly type a total of 241 lineage I isolates. The MLGT assay provided high discriminatory power (Simpson's index value, 0.91), uniquely identified isolates from the eight listeriosis outbreaks examined, and differentiated serotypes 1/2b and 4b as well as epidemic clone I (ECI), ECIa, and ECII. In addition, the assay included probes for a previously characterized truncation mutation in inlA, providing for the identification of a specific virulence-attenuated subtype. These results demonstrate that MLGT represents a significant new tool for use in pathogen surveillance, outbreak detection, risk assessment, population analyses, and epidemiological investigations. DNA sequences were deposited in the GenBank database under accession numbers DQ 812146 to DQ 812517, DQ 843664 to DQ 844598, and AY 512391 to AY 512502.

Bacterial Proteins↗

PubMed1988

Role of hemolysin for the intracellular growth of Listeria monocytogenes.

Listeria monocytogenes insertion mutants defective in hemolysin production were generated using the conjugative transposons Tn916 and Tn1545. All of the nonhemolytic mutants (hly-) lacked a secreted 58-kD polypeptide, presumedly hemolysin, and were avirulent in a mouse model. An intracellular multiplication assay was established in monolayers of mouse bone marrow-derived macrophages, the J774 macrophage-like cell line, the CL.7 embryonic mouse fibroblast cell line, and the Henle 407 human epithelial cell line. The hly+ strain grew intracellularly in all of the tissue culture cells with a doubling time of approximately 60 min. In contrast, the hly- mutants failed to grow in the murine-derived tissue culture cells, but retained the ability to grow in the human tissue culture cells examined. Hemolytic-positive revertants were selected after passage of the hly- mutants through monolayers of J774 cells. In each case, the hemolytic revertants possessed the 58-kD polypeptide, were capable of intracellular growth in tissue culture monolayers and were virulent for mice.

Animals↗

PubMed1997

Proteolytic pathways of activation and degradation of a bacterial phospholipase C during intracellular infection by Listeria monocytogenes.

Listeria monocytogenes is a facultative intracellular bacterial pathogen that spreads cell to cell without exposure to the extracellular environment. Bacterial cell-to-cell spread is mediated in part by two secreted bacterial phospholipases C (PLC), a broad spectrum PLC (PC-PLC) and a phosphatidylinositolspecific PLC (PI-PLC). PI-PLC is secreted in an active state, whereas PC-PLC is secreted as an inactive proenzyme (proPC-PLC) whose activation is mediated in vitro by an L. monocytogenes metalloprotease (Mpl). Analysis of PI-PLC, PC-PLC, and Mpl single and double mutants revealed that Mpl also plays a role in the spread of an infection, but suggested that proPC-PLC has an Mpl-independent activation pathway. Using biochemical and microscopic approaches, we describe three intracellular proteolytic pathways regulating PCPLC activity. Initially, proPC-PLC secreted in the cytosol of infected cells was rapidly degraded in a proteasome-dependent manner. Later during infection, PCPLC colocalized with bacteria in lysosome-associated membrane protein 1-positive vacuoles. Activation of proPC-PLC in vacuoles was mediated by Mpl and an Mpl-independent pathway, the latter being sensitive to inhibitors of cysteine proteases. Lastly, proPC-PLC activation by either pathway was sensitive to bafilomycin A1, a specific inhibitor of vacuolar ATPase, suggesting that activation was dependent on acidification of the vacuolar compartment. These results are consistent with a model in which proPC-PLC activation is compartment specific and controlled by a combination of bacterial and host factors.

Animals↗

PubMed1994

Glycine betaine confers enhanced osmotolerance and cryotolerance on Listeria monocytogenes.

Listeria monocytogenes is a gram-positive food-borne pathogen that is notably resistant to osmotic stress and can grow at refrigerator temperatures. These two characteristics make it an insidious threat to public health. Like several other organisms, L. monocytogenes accumulates glycine betaine, a ubiquitous and effective osmolyte, intracellularly when grown under osmotic stress. However, it also accumulates glycine betaine when grown under chill stress at refrigerator temperatures. Exogenously added glycine betaine enhances the growth rate of stressed but not unstressed cells, i.e., it confers both osmotolerance and cryotolerance. Both salt-stimulated and cold-stimulated accumulation of glycine betaine occur by transport from the medium rather than by biosynthesis. Direct measurement of glycine betaine uptake shows that cells transport betaine 200-fold faster at high salt concentration (4% NaCl) than without added salt and 15-fold faster at 7 than at 30 degrees C. The kinetics of glycine betaine transport suggest that the two transport systems are indistinguishable in terms of affinity for betaine and may be the same. Hyperosmotic shock and cold shock experiments suggest the transport system(s) to be constitutive; activation was not blocked by chloramphenicol. A cold-activated transport system is a novel observation and has intriguing implications concerning the physical state of the cell membrane at low temperature.

Adaptation, Physiological↗

PubMed2004

Regulation of transcription of compatible solute transporters by the general stress sigma factor, sigmaB, in Listeria monocytogenes.

Listeria monocytogenes is well known for its durable physiological characteristics, which allow the organism to grow at low temperature and pH and high osmolarity. Growth under high osmolarity depends on the accumulation of compatible solutes, among which glycine betaine and carnitine are the preferred solutes for this organism. Three different transport systems, Gbu, BetL, and OpuC, have been identified in L. monocytogenes which serve to scavenge the preferred compatible solutes. The general stress response regulator sigma(B) has been shown to play an important role in osmotic adaptation in L. monocytogenes, presumably by directing transcription from one or more of the solute transport genes. In the studies presented here, we have used primer extension analyses to identify the promoter elements responsible for transcription of the opuC, gbuA, and betL genes. All three genes are osmotically inducible to some degree. betL is transcribed from a sigma(B)-independent promoter, while gbuA is transcribed from dual promoters, one of which is sigma(B) dependent. opuC is transcribed exclusively from a sigma(B)-dependent promoter. The betL promoter is similar in sequence to the sigma(B)-independent gbuAP1 promoter. Kinetic analysis of transcript accumulation after osmotic upshift demonstrated that sigma(B)-dependent transcripts from gbuAP2 and sigB accumulate for an extended period after upshift, suggesting that sigma(B) activity may provide a mechanism for sustained high-level expression during osmotic challenge. In contrast to osmotic upshift, expression from the sigma(B)-dependent opuC and gbuAP2 promoters after temperature upshift and ethanol stress was minimal, suggesting that additional mechanisms may also participate in regulating transcription from these sigma(B)-dependent promoters.

ATP-Binding Cassette Transporters↗

PubMed2000

The use of listeriolysin to identify in vivo induced genes in the gram-positive intracellular pathogen Listeria monocytogenes.

Listeria monocytogenes is capable of growth within the cytoplasm of infected host cells. Escape from the host cell phagosome is mediated primarily through secretion of listeriolysin, a haemolytic factor which functions to actively lyse the phagosomal membrane. Listeriolysin negative mutants of L. monocytogenes are non-haemolytic on blood agar plates and demonstrate a significant reduction of virulence in the mouse model of infection. We have developed a system for the identification of in vivo induced genes in L. monocytogenes which utilizes the listeriolysin gene, hly, as both a reporter of gene expression and as a means of selection of promoter elements expressed in vivo. The system is analogous to in vivo expression technology (IVET) first reported for Salmonella, however, as listeriolysin functions in the environment of the host phagosome the loci identified in this study are most likely expressed during residence in the phagosome. The system was successfully tested using the promoter of the inducible virulence gene plcA. A bank was created by fusing a promoterless copy of hly to random promoter elements in a listeriolysin negative IVET host. Sequential inoculations of mice with this bank resulted in the isolation of clones with increased survival potential in the mouse model relative to a negative control, but which remained haemolysin negative on blood agar plates. Nine in vivo induced loci were identified including genes encoding a DNA topoisomerase III, a cellobiose transporter and a fumarase. Two isolates represented fusions to proteins of unknown function and three isolates contained no significant homologues in the database. A mutant in the fumarase gene demonstrated reduced virulence for mice and an inability to grow in cultured mouse phagocytes.

Animals↗

PubMed1996

The pathogenesis of infection by Listeria monocytogenes.

Listeria monocytogenes is a Gram-positive bacterium responsible for severe infections in human and a large variety of animal species. It is a facultative intracellular pathogen which invades macrophages and most tissue cells of infected hosts where it can proliferate. The molecular basis of this intracellular parasitism has been to a large extent elucidated. The virulence factors, including internalin, listeriolysin O, phospholipases and a bacterial surface protein, ActA, are encoded by chromosomal genes organised in operons. Following internalisation into host cells, the bacteria escape from the phagosomal compartment and enter the cytoplasm. They then spread from cell to cell by a process involving actin polymerisation. In infected hosts, the bacteria cross the intestinal wall at Peyer's patches to invade the mesenteric lymph nodes and the blood. The main target organ is the liver, where the bacteria multiply inside hepatocytes. Early recruitment of polymorphonuclear cells lead to hepatocyte lysis, and thereby bacterial release. This causes prolonged septicaemia, particularly in immunocompromised hosts, thus exposing the placenta and brain to infection. The prognosis of listeriosis depends on the severity of meningoencephalitis, due to the elective location of foci of infection in the brain stem (rhombencephalitis). Despite bactericidal antibiotic therapy, the overall mortality is still high (25 to 30%).

Actins↗