Old people who ignore 'use by' dates run the risk of being exposed to the deadly listeria bacteria, the Government's food watchdog the Food Standards Agency has warned.

The bacterium Listeria monocytogenes is ubiquitous in the environment and can lead to severe food-borne infections. It has recently emerged as a multifaceted model in pathogenesis. However, how this bacterium switches from a saprophyte to a pathogen is largely unknown. Here, using tiling arrays and RNAs from wild-type and mutant bacteria grown in vitro, ex vivo and in vivo, we have analysed the transcription of its entire genome. We provide the complete Listeria operon map and have uncovered far more diverse types of RNAs than expected: in addition to 50 small RNAs (<500 nucleotides), at least two of which are involved in virulence in mice, we have identified antisense RNAs covering several open-reading frames and long overlapping 5' and 3' untranslated regions. We discovered that riboswitches can act as terminators for upstream genes. When Listeria reaches the host intestinal lumen, an extensive transcriptional reshaping occurs with a SigB-mediated activation of virulence genes. In contrast, in the blood, PrfA controls transcription of virulence genes. Remarkably, several non-coding RNAs absent in the non-pathogenic species Listeria innocua exhibit the same expression patterns as the virulence genes. Together, our data unravel successive and coordinated global transcriptional changes during infection and point to previously unknown regulatory mechanisms in bacteria.

Because bacteriophages generally parasitize only closely related bacteria, it is assumed that phage-mediated genetic exchange occurs primarily within species. Here we report that staphylococcal pathogenenicity islands, containing superantigen genes, and other mobile elements transferred to Listeria monocytogenes at the same high frequencies as they transfer within Staphylococcus aureus. Several staphylococcal phages transduced L. monocytogenes but could not form plaques. In an experiment modeling phage therapy for bovine mastitis, we observed pathogenicity island transfer between S. aureus and L. monocytogenes in raw milk. Thus, phages may participate in a far more expansive network of genetic information exchange among bacteria of different species than originally thought, with important implications for the evolution of human pathogens.

Listeria monocytogenes is a Gram-positive, intracellular, food-borne pathogen that can cause severe illness in humans and animals. On infection, it is actively phagocytosed by macrophages1; it then escapes from the phagosome, replicates in the cytosol, and subsequently spreads from cell to cell by a non-lytic mechanism driven by actin polymerization2. Penetration of the phagosomal membrane is initiated by the secreted haemolysin listeriolysin O (LLO), which is essential for vacuolar escape in vitro and for virulence in animal models of infection3. Reduction is required to activate the lytic activity of LLO in vitro 4, 5, 6, and we show here that reduction by the enzyme gamma-interferon-inducible lysosomal thiol reductase (GILT, also called Ifi30) is responsible for the activation of LLO in vivo. GILT is a soluble thiol reductase expressed constitutively within the lysosomes of antigen-presenting cells7, 8, and it accumulates in macrophage phagosomes as they mature into phagolysosomes9. The enzyme is delivered by a mannose-6-phosphate receptor-dependent mechanism to the endocytic pathway, where amino- and carboxy-terminal pro-peptides are cleaved to generate a 30-kDa mature enzyme7, 8, 10. The active site of GILT contains two cysteine residues in a CXXC motif that catalyses the reduction of disulphide bonds7, 8. Mice lacking GILT are deficient in generating major histocompatibility complex class-II-restricted CD4+ T-cell responses to protein antigens that contain disulphide bonds11, 12. Here we show that these mice are resistant to L. monocytogenes infection. Replication of the organism in GILT-negative macrophages, or macrophages expressing an enzymatically inactive GILT mutant, is impaired because of delayed escape from the phagosome. GILT activates LLO within the phagosome by the thiol reductase mechanism shared by members of the thioredoxin family. In addition, purified GILT activates recombinant LLO, facilitating membrane permeabilization and red blood cell lysis. The data show that GILT is a critical host factor that facilitates L. monocytogenes infection.

Pathogens have many ways of subverting their hosts' molecular machinery. A striking example of such a ploy comes to light from investigations of the species of bacterium that causes listeriosis. A recent outbreak of Listeria monocytogenes infection in Canada1 has to date claimed 20 lives out of 53 cases and is a stark reminder that these bacteria pose a serious threat to public health. Ingestion of contaminated food can have especially serious consequences for those at high risk — pregnant women, newborns, the elderly, and individuals with compromised immune systems. A better understanding of L. monocytogenes will depend on insight into the interaction between the bacterium and its host at the cellular level. Typically, bacteria are engulfed by macrophages, versatile agents of the immune system. They are then contained in a cellular compartment called a phagosome, which gradually becomes acidified and fuses with a compartment containing digestive enzymes, the lysosome, destroying the invader in the resulting phagolysosome. However, L. monocytogenes can avoid destruction by escaping through the phagosomal membrane into the cell cytosol, where it replicates and goes on to infect neighbouring cells. The key player in the escape process is the bacterial virulence factor, listeriolysin O (LLO). On page 1244 of this issue, Singh et al.2 reveal that L. monocytogenes takes advantage of a host factor to promote LLO activity during infection.

The ability to cross host barriers is an essential virulence determinant of invasive microbial pathogens. Listeria monocytogenes is a model microorganism that crosses human intestinal and placental barriers, and causes severe maternofetal infections by an unknown mechanism1. Several studies have helped to characterize the bacterial invasion proteins InlA and InlB2. However, their respective species specificity has complicated investigations on their in vivo role3, 4. Here we describe two novel and complementary animal models for human listeriosis: the gerbil, a natural host for L. monocytogenes, and a knock-in mouse line ubiquitously expressing humanized E-cadherin. Using these two models, we uncover the essential and interdependent roles of InlA and InlB in fetoplacental listeriosis, and thereby decipher the molecular mechanism underlying the ability of a microbe to target and cross the placental barrier.

This review rather than covering the whole field intends to highlight recent findings on the Listeria monocytogenes infectious process or some Listeria specific traits, place them within the framework of well-established data, and demonstrate how this Gram-positive bacterium has, in two decades, emerged as a multifaceted paradigm. Indeed, the cell biology of the infectious process has been deciphered in great detail and provided insights in both the way bacterial pathogen manipulate the host and unsuspected functions of well-known cellular proteins. The intra- and intercellular motility has in particular been instrumental in understanding actin-based motility in general. The analysis of the two main Listeria invasion proteins and that of their host specificities have illustrated how in vitro studies can help generating or choosing relevant animal models for in vivo studies. Listeria post-genomics studies have highlighted the power of comparative genomics in virulence studies. Together, Listeria, after being recognized as a powerful tool in immunology, now appears as one of the most insightful models in infection biology.

The invariant (i) NKT cells represent unique T lymphocytes expressing TCRVα14. Although iNKT cells have been regarded as T lymphocytes expressing NK1.1, they do not consistently express this marker. NK1.1 allows recognition of “missing-self” and thus controls inhibition/activation of iNKT cells. It is thus tempting to assume that iNKT cells participate in the regulation of host immune responses during microbial infection by controlling NK1.1 expression. These findings shed light on the unique role of iNKT cells in microbial infection and provide an evidence for unique aspects of the NK1.1 on these cells as a regulatory molecule.

a bit bogus as they make "Tem" in vitro and Tcm don't protect at all (CFSE-LselhiCD127+) BUT Teff, Tem protect

The purinoreceptor P2X7 is expressed on subsets of T cells and mediates responses of these cells to extracellular nucleotides such as ATP or NAD(+). We identified P2X7 as a molecule highly up-regulated on conventional CD8alphabeta(+) and unconventional CD8alphaalpha(+) T cells of the intestinal epithelium of mice. In contrast, CD8(+) T cells derived from spleen, mesenteric lymph nodes, and liver expressed only marginal levels of P2X7. However, P2X7 was highly up-regulated on CD8(+) T cells from spleen and lymph nodes when T cells were activated in the presence of retinoic acid. High P2X7 expression on intestinal CD8(+) T cells as well as on CD8(+) T cells incubated with retinoic acid resulted in enhanced sensitivity of cells to extracellular nucleotides. Both cell populations showed a high level of apoptosis following incubation with NAD(+) and the ATP derivative 2',3'-O-(benzoyl-4-benzoyl)-ATP, and injection of NAD(+) caused selective in vivo depletion of intestinal CD8(+) T cells. Following oral infection with Listeria monocytogenes, P2X7-deficient mice showed similar CD8(+) T cell responses in the spleen, but enhanced responses in the intestinal mucosa, when compared with similarly treated wild-type control mice. Overall, our observations define P2X7 as a new regulatory element in the control of CD8(+) T cell responses in the intestinal mucosa.