Maïwenn Olier

Assessment of the pathogenic potential of two Listeria monocytogenes human faecal carriage isolates.

Two human faeces carriage isolates of Listeria monocytogenes (H1 and H2) were compared to reference strains (ScottA and LO28) with regard to their lethality in 14-day-old chick embryos, their haemolytic and phospholipase (phosphatidylcholine-phospholipase C and phosphatidylinositol-phospholipase C) activities and their invasiveness towards Caco-2 cells. Experimental infection of chick embryos allowed discrimination of the strains into those exhibiting high virulence (ScottA and H2), those exhibiting slightly attenuated virulence (LO28) and those exhibiting low virulence (H1). A similar percentage mortality and time to death for embryos was observed when they were infected with H2 as was seen with infection by the reference strain ScottA. Therefore, human carriage strain H2 was considered potentially pathogenic. In contrast to H2 and ScottA, H1 exhibited low virulence. Using the tissue-culture cell-line model, it was found that carriage strain H1 was unable to enter Caco-2 cells efficiently, even though it was similar to the virulent strains in terms of the enzymic activities involved in pathogenicity. Detection of the internalins InlA and InlB, involved in the internalization of L. monocytogenes in the host cells, by immunoblot indicated that a truncated form of InlA was produced by H1. Taken together, these data provide a starting point for the study of the behaviour of two types of human faeces carriage strains and their characterization.

Expression of Truncated Internalin A Is Involved in Impaired Internalization of Some Listeria monocytogenes Isolates Carried Asymptomatically by Humans

ABSTRACT Fourteen human carriage Listeria monocytogenes isolates were compared to sporadic and epidemic-associated human strains in order to ascertain the pathogenic behavior of these unrecognized asymptomatic strains. Experimental infection of 14-day-old chick embryos revealed that the majority of the carriage strains were attenuated for virulence. Of the 10 attenuated carriage strains, 5 were affected in their invasion capacities in vitro. Western blot analysis with antibody directed against InlA, the surface protein implicated in the internalization in host cells, allowed correlation between the ability of the carriage strains to enter Caco-2 cells and InlA expression. Indeed, these five carriage strains produced truncated forms of InlA. Four of the five truncated forms of InlA had an apparent molecular mass of 47 kDa. In order to assess the existence of a genetic lineage, partial sequences of inlA gene of these four strains were compared and revealed that they had a high degree of sequence conservation at the gene (99.86%) and amino acid (100%) levels. Comparison of their nucleotide sequences with that of the corresponding segment of inlA from EGD-e and Scott A strains, taken as epidemic references, showed more divergence. Taken together, these observations suggest the presence of specific traits that characterize L. monocytogenes strains isolated during asymptomatic carriage. Some of these traits could provide some explanations about the determinants that make them unable to cause systemic human infection.

Truncated Internalin A and Asymptomatic Listeria monocytogenes Carriage: In Vivo Investigation by Allelic Exchange

ABSTRACT Allelic exchange of the region coding for the C terminus of InlA between one epidemic (with an 80-kDa InlA) and one asymptomatic (with a 47-kDa InlA) carriage Listeria monocytogenes strain confirmed the need for this region for internalin entry in vitro. Interestingly, restoration of internalin A functionality did not result in full virulence in chicken embryo assays.

Oral Tolerance Failure upon Neonatal Gut Colonization with Escherichia coli Producing the Genotoxin Colibactin

ABSTRACT The intestinal barrier controls the balance between tolerance and immunity to luminal antigens. When this finely tuned equilibrium is deregulated, inflammatory disorders can occur. There is a concomitant increase, in urban populations of developed countries, of immune-mediated diseases along with a shift in Escherichia coli population from the declining phylogenetic group A to the newly dominant group B2, including commensal strains producing a genotoxin called colibactin that massively colonized the gut of neonates. Here, we showed that mother-to-offspring early gut colonization by colibactin-producing E. coli impairs intestinal permeability and enhances the transepithelial passage of luminal antigen, leading to an increased immune activation. Functionally, this was accompanied by a dramatic increase in local and systemic immune responses against a fed antigen, decreased regulatory T cell population, tolerogenic dendritic cells, and enhanced mucosal delayed-type hypersensitivity response. Conversely, the abolition of colibactin expression by mutagenesis abrogates the alteration of oral tolerance induced by neonatal colonization by E. coli. In conclusion, the vertical colonization by E. coli producing the genotoxin colibactin enhances intestinal translocation and subsequently alters oral tolerance. Thus, early colonization by E. coli from the newly dominant phylogenetic group B2, which produces colibactin, may represent a risk factor for the development of immune-mediated diseases.

Mo1302 In vivo Evaluation of Properties of a New Medical Device Against Intestinal Commensals With Uropathogenic Potential

number: 2439405. Title: In vivo evaluation of properties of a new medical device against intestinal commensals with uropathogenic potential Maïwenn Olier, Soraya Sekkal, Cherryl Harkat, Hélène Eutamène, Vassilia Theodorou, Lionel Bueno. UMR 1331 Toxalim, INRA/INPT/UPS, Neuro-Gastroenterology and Nutrition Group, Toulouse, France.  Deceased Background: Based on protecting intestinal mucosa properties, a cross-linked protein compound, is a new medical device for the control and prevention of urinary tract infections. Considering that intestinal microbiota is a common immediate source of uropathogens, we evaluated the antagonistic activity of this product to limit the intestinal commensal bacterial communities with uropathogenic potential in feces of treated rats, decreasing their contact with the intestinal mucosa. Methods: Female Wistar rats were orally fed for 4 days either with the product (7500 mg kg , day, p.o) or vehicle (water plus Na2CO3, p.o). E. coli population and other Enterobacteriaceae such as Klebsiella spp., Enterobacter ssp., Serratia ssp., Citrobacter ssp. (named collectively KESC), Enterococcus ssp. or Proteeae ssp. were enumerated from feces collected throughout the course of the experiment by using selective chromogenic agar plates. Monitoring of fecal E. coli levels was additionally performed in streptomycin-pretreated rats highly colonized with a streptomycin-resistant human commensal O1:K1 E. coli strain sharing some common genetic traits of archetypal uropathogenic E. coli strains. Results: The treatment with the product resulted in a significant reduction of fecal endogenous E. coli (2.89+/-0.61 vs. 4.04+/-0.09 Log10 CFU/g feces, p<0.05) and Enterococcus spp. (3.77+/-0.29 vs. 5.24+/-0.12 Log10 CFU/g feces, p<0.01) levels without affecting other detected fecal opportunistic uropathogens. Antagonistic property of the product was additionally confirmed in feces of rats highly colonized with the O1:K1 E. coli strain (5.09+/-0.25 vs. 6.56+/-0.33 Log10 CFU/g feces, p<0.001). Conclusion: A cross linked protein product through its ability to reduce the risk of urinary tract infections by altering intestinal niche occupied by opportunistic uropathogens such as E. coli or Enterococcus spp may be a promising candidate in the management of urinary infections.