Solène Grayo

Bio: Solène Grayo is an academic researcher from Pasteur Institute. The author has contributed to research in topics: Listeria monocytogenes & Moxifloxacin. The author has an hindex of 6, co-authored 8 publications receiving 393 citations. Previous affiliations of Solène Grayo include French Institute of Health and Medical Research & World Health Organization.

Conjugated action of two species-specific invasion proteins for fetoplacental listeriosis

Abstract: Listeriosis and other microbial infections in pregnancy can affect the fetus as well as the mother, but little is known about how pathogens cross the placental barrier. Disson et al. investigated the process using two complementary animal models infected by Listeria monocytogenes. They show that two virulence factors or invasion proteins, InlA and InlB, are required for the transfer of pathogen to the placenta. Thus by blocking one or both of these pathways it may be possible to stop microbes passing into the fetus. Conversely, it may be possible to exploit these pathways to target therapeutic molecules across the same barrier. Listeria monocytogenes can cross the placental barrier and may result in fetal or neonatal mortality. Using two complementary animal models, it is now shown that virulence factors InlA and InlB are both required for this process in vivo. 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.

Modeling human listeriosis in natural and genetically engineered animals

Abstract: Listeria monocytogenes causes listeriosis, a human foodborne infection leading to gastroenteritis, meningoencephalitis and maternofetal infections. InlA and InlB, two L. monocytogenes surface proteins, interact with their respective receptors E-cadherin and Met and mediate bacterial entry into human cultured cells. Here, we present protocols for studying listeriosis in three complementary animal models: (i) the human E-cadherin (hEcad) transgenic mouse line; (ii) the knock-in E16P mouse line; and (iii) the gerbil, in which both InlA–E-cadherin and InlB–Met species-specific interactions occur as in humans. Two routes of infection are described: oral inoculation, the natural route for infection; and intravenous inoculation that bypasses the intestinal barrier. We describe how to monitor L. monocytogenes infection, both qualitatively by imaging techniques and quantitatively by bacterial enumeration. The advantage of these methods over the classical intravenous inoculation of L. monocytogenes in wild-type mice (in which the InlA–E-cadherin interaction does not occur) is that it allows the pathophysiology of listeriosis to be studied in animal models relevant to humans, as they are permissive to the interactions that are thought to mediate L. monocytogenes crossing of human host barriers. The whole procedure (inoculation, in vivo imaging, bacterial enumeration, histopathology) takes one full week to complete, including 3 d of actual experiments.

PI3-kinase activation is critical for host barrier permissiveness to Listeria monocytogenes

Abstract: Invasion of nonphagocytic cells, a critical property of Listeria monocytogenes (Lm) that enables it to cross host barriers, is mediated by the interaction of two bacterial surface proteins, InlA and InlB, with their respective receptors E-cadherin and c-Met. Although InlA-E-cadherin interaction is necessary and sufficient for Lm crossing of the intestinal barrier, both InlA and InlB are required for Lm crossing of the placental barrier. The mechanisms underlying these differences are unknown. Phosphoinositide 3-kinase (PI3-K) is involved in both InlA- and InlB-dependent pathways. Indeed, InlA-dependent entry requires PI3-K activity but does not activate it, whereas InlB-c-Met interaction activates PI3-K. We show that Lm intestinal target cells exhibit a constitutive PI3-K activity, rendering InlB dispensable for InlA-dependent Lm intestinal barrier crossing. In contrast, the placental barrier does not exhibit constitutive PI3-K activity, making InlB necessary for InlA-dependent Lm placental invasion. Here, we provide the molecular explanation for the respective contributions of InlA and InlB to Lm host barrier invasion, and reveal the critical role of InlB in rendering cells permissive to InlA-mediated invasion. This study shows that PI3-K activity is critical to host barrier permissiveness to microbes, and that pathogens exploit both similarities and differences of host barriers to disseminate.

Comparison of the In Vitro Efficacies of Moxifloxacin and Amoxicillin against Listeria monocytogenes

Abstract: Listeria monocytogenes is a facultative intracellular bacterium that causes severe infections associated with a high mortality rate. Moxifloxacin presents extended activity against gram-positive bacteria and has recently been suggested to be a potential alternative in the treatment of listeriosis. We evaluated the in vitro efficacy of moxifloxacin against L. monocytogenes using a combination of epidemiological and experimental approaches. The median MIC of moxifloxacin for a large collection of L. monocytogenes strains of various origins (human, food, and environment) was 0.5 microg/ml (MIC range, 0.064 to 1 microg/ml). No differences were observed, irrespective of the origin of the strains. Moreover, no cross-resistance with fluoroquinolones was detected in strains that have been reported to be resistant to ciprofloxacin. The in vitro activities of moxifloxacin and amoxicillin were compared by time-kill curve and inhibition of intracellular growth experiments by using a model of bone marrow-derived mouse macrophages infected by L. monocytogenes EGDe. Both moxifloxacin and amoxicillin were bactericidal in broth against extracellular forms of L. monocytogenes. However, moxifloxacin acted much more rapidly, beginning to exert its effects in the first 3 h and achieving complete broth sterilization within 24 h of incubation. Moxifloxacin has a rapid bactericidal effect against intracellular reservoirs of bacteria, whereas amoxicillin is only bacteriostatic and appears to prevent cellular lysis and the subsequent bacterial spreading to adjacent cells. No resistant bacteria were selected during the in vitro experiments. Taken together, our results suggest that moxifloxacin is an interesting alternative to the reference treatment, combining rapid and bactericidal activity, even against intracellular bacteria.

Rapid eradication of Listeria monocytogenes by moxifloxacin in a murine model of central nervous system listeriosis.

Abstract: Listeriosis is a rare but life-threatening infection. A favorable outcome is greatly aided by early administration of antibiotics with rapid bactericidal activity against Listeria monocytogenes. Moxifloxacin, a new-generation fluoroquinolone with extended activity against gram-positive bacteria, has proved its effectiveness in vitro against intracellular reservoirs of bacteria. The efficacies of moxifloxacin and amoxicillin were compared in vivo by survival curve assays and by studying the kinetics of bacterial growth in blood and organs in a murine model of central nervous system (CNS) listeriosis. We combined pharmacokinetic and pharmacodynamic approaches to correlate the observed efficacy in vivo with plasma and tissue moxifloxacin concentrations. Death was significantly delayed for animals treated with a single dose of moxifloxacin compared to a single dose of amoxicillin. We observed rapid bacterial clearance from blood and organs of animals treated with moxifloxacin. The decrease in the bacterial counts in blood and brain correlated with plasma and cerebral concentrations of antibiotic. Moxifloxacin peaked in the brain at 1.92 +/- 0.32 microg/g 1 hour after intraperitoneal injection. This suggests that moxifloxacin rapidly crosses the blood-brain barrier and diffuses into the cerebral parenchyma. Moreover, no resistant strains were selected during in vivo experiments. Our results indicate that moxifloxacin combines useful pharmacokinetic properties and rapid bactericidal activity and that it may be a valuable alternative for the treatment of CNS listeriosis.

Listeria monocytogenes, a food-borne pathogen

Abstract: Listeria monocytogenes is a Gram positive, aerobic, facultative anaerobic and nonacid fast bacterium, which can cause the disease listeriosis in both human and animals. It is widely distributed thoroughout the environment and has been isolated from various plant and animal food products associated with listeriosis outbreaks. Contaminated ready-to-eat food products such as gravad and cold-smoked salmon and rainbow trout have been associated with human listeriosis in Sweden. The aim of this study was to analyse the occurrence and level of L. monocytogenes in gravad and cold-smoked salmon (Salmo salar) products packed under vacuum or modified atmosphere from retail outlets in Sweden. Isolated strains were characterized by serotyping and the diversity of the strains within and between producers were determined with PFGE (Pulsed-field gel electrophoresis). The characterized fish isolates were compared with previously characterized human strains. L. monocytogenes was isolated from 11 (three manufacturers) of 56 products analysed. This included gravad salmon products from three manufacturers and cold-smoked salmon from one manufacturer. The highest level of L. monocytogenes found was 1500 cfu/g from a cold-smoked salmon product but the level was low (<100 cfu/g) in most of the products. Serovar 1/2a was predominant, followed by 4b. Three products of gravad salmon harboured more than one serovar. PFGE typing of the 56 salmon isolates detected five Asc I types: four types were identical to human clinical strains with Asc I and one was identical and one was closely related to human clinical strains with Apa I. Isolation of identical or closely related L. monocytogenes strains from human clinical cases of listeriosis and gravad and cold-smoked salmon suggested that these kinds of products are possible sources of listeriosis in Sweden. Therefore, these products should be considered risk products for human listeriosis.

The Merck Index

Abstract: The Merck Index of Chemicals and Drugs An Encyclopedia for the Chemist, Pharmacist, Physician and Allied Professions Sixth edition Pp xiv + 1167 (Rahway, NJ: Merck and Company, Inc, 1952) 750 dollars; thumb-indexed, 8 dollars

The Listeria transcriptional landscape from saprophytism to virulence

Abstract: 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.