Lysogeny with Shiga Toxin 2-Encoding Bacteriophages Represses Type III Secretion in Enterohemorrhagic Escherichia coli

Lytic or lysogenic infections by bacteriophages drive the evolution of enteric bacteria. Enterohemorrhagic Escherichia coli (EHEC) have recently emerged as a significant zoonotic infection of humans with the main serotypes carried by ruminants. Typical EHEC strains are defined by the expression of a type III secretion (T3S) system, the production of Shiga toxins (Stx) and association with specific clinical symptoms. The genes for Stx are present on lambdoid bacteriophages integrated into the E. coli genome. Phage type (PT) 21/28 is the most prevalent strain type linked with human EHEC infections in the United Kingdom and is more likely to be associated with cattle shedding high levels of the organism than PT32 strains. In this study we have demonstrated that the majority (90%) of PT 21/28 strains contain both Stx2 and Stx2c phages, irrespective of source. This is in contrast to PT 32 strains for which only a minority of strains contain both Stx2 and 2c phages (28%). PT21/28 strains had a lower median level of T3S compared to PT32 strains and so the relationship between Stx phage lysogeny and T3S was investigated. Deletion of Stx2 phages from EHEC strains increased the level of T3S whereas lysogeny decreased T3S. This regulation was confirmed in an E. coli K12 background transduced with a marked Stx2 phage followed by measurement of a T3S reporter controlled by induced levels of the LEE-encoded regulator (Ler). The presence of an integrated Stx2 phage was shown to repress Ler induction of LEE1 and this regulation involved the CII phage regulator. This repression could be relieved by ectopic expression of a cognate CI regulator. A model is proposed in which Stx2-encoding bacteriophages regulate T3S to co-ordinate epithelial cell colonisation that is promoted by Stx and secreted effector proteins

Development and characterization of an in vivo skin photomicronucleus assay in rats

For pharmaceuticals, current regulatory guidance for photosafety testing states that studies are warranted for drug candidates that both absorb light in the range of 290-700 nm and that are either applied topically or reach the skin or eyes by systemic exposure. In contrast to standard genotoxicity evaluations, where a positive (or equivocal) result in vitro can be placed into context with additional testing in vivo, there are no equivalent short-term in vivo photogenotoxicity assays in the current photosafety test battery. Therefore, a short-term in vivo assay for the evaluation of a photogenotoxic potential in the skin, the target organ for photocarcinogenicity, was developed in rats. After oral 8-methoxypsoralen administration, rats were exposed to ultraviolet radiation and sacrificed 3 days after treatment to isolate epidermal cells for subsequent micronucleus (MN) evaluation. Optimal conditions were determined to obtain maximal induction of MN, followed by demonstrating feasibility and reproducibility of the method. The results of the present study indicate that the in vivo rat skin photomicronucleus test may be a promising tool for detection of photoclastogenicity. Given the association between MN induction and cancer, the assay may also provide a promising tool for the early detection of photocarcinogenesis and help bridge the gap in the existing photosafety testing paradigm. © The Author 2010. Published by Oxford University Press on behalf of the UK Environmental Mutagen Society. All rights reserved

Proliferative and Non-Proliferative Lesions of the Rat and Mouse Soft Tissue, Skeletal Muscle and Mesothelium

The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying lesions observed in the soft tissues including skeletal muscle as well as the mesothelium of rats and mice. The standardized nomenclature of lesions presented in this document is also available electronically on the Internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous developmental and aging lesions as well as those induced by exposure to test materials. A widely accepted and utilized international harmonization of nomenclature for lesions in soft tissues, skeletal muscle and mesothelium in laboratory animals will decrease confusion among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists

Genome Plasticity in Pathogenic and Nonpathogenic Enterobacteria

The Enterobacteriaceae comprise a distinct phylogenetic cluster that share a common ancestor with other γ-Proteobacteria. This prokaryotic family comprises 40 genera with 200 species (Garrity 2001). Within this division many representatives live in intimate association with hosts either as pathogens, as commensals or as symbionts (Steinert et al. 2000). The best-studied examples are the entero-bacteria, which comprise the clinically relevant human and animal pathogenic species Escherichia coli, Salmonella enterica, and Shigella spp., as well as Yersinia pestis, Y. pseudotuberculosis and Y. enterocolitica. The entomopathogenic bacterium Photorhabdus luminescens also belongs to the Enterobacteriaceae. This bacterium is unusual in that it combines a symbiotic life style within the guts of nematodes with a pathogenic life style that results in the killing of insects. Among the γ-Proteobacteria there are many species establishing symbiotic interactions mostly with invertebrate hosts, for example with insects, with bioluminescent squid and other marine invertebrates, and with nematodes. The genomes of several pathogens and symbionts have been sequenced recently and work is still in progress. In spite of the diverse manifestations of bacteria-host interactions, there are similar fundamental mechanisms that mediate the interaction and communication between the bacterial and eukaryotic partners (Hentschel et al. 2000; Steinert et al. 2000)