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A bacteriophage ([PHI]IF3) capable of mediating generalized transduction in Serratia marcescens strain Db11 has been isolated and characterized. The genome of this Serratia strain has recently been sequenced and is likely to become the reference strain for S. marcescens researchers. [PHI]IF3 is most likely a virulent phage, which can transduce markers at frequencies of [10.sup.-6] transductants per p.f.u. It has a lipopolysaccharide receptor and was determined to have a latent period of 50 rain and a burst size of approximately 100 phages. The phage DNA was resistant to digestion with restriction enzymes. Electron microscopy showed [PHI]IF3 to be a member of the family Myoviridae. This is the first report of a generalized transducing phage able to infect Db11 and this phage will be a valuable tool for functional genomic analysis of the pathogen host.

The genetic screens that facilitate that identification of pathogen virulence factors are summarized and the existing and emerging genetically tractable host models are compared. It is seen that the widest possible range of model hosts and analytical methods should be used for investigating the host-pathogen interactions.

Results show that bfrZ gene of Bordetella bronchiseptica encodes a TonB-dependent receptor for siderophore, whose expression is controlled by BupI-BupR sigma-antisigma transcription factors. Data indicate that binding event of a siderophore to bfrZ sends a signal to BupI inducing bfrZ transcription.

Research was conducted to identify an AraC-type transcriptional regulator used in the alcaligin siderophore synthesis in Bordetella pertussis and Bordetella bronchiseptica. In this study, DNA fragments that feature Fur binding sites were isolated from a partial B. bronchiseptica genomic DNA library using a Fur titration assay. Results show that AlcR regulator does not influence the mouse respiratory infection model as well as the production of major virulence factors.

Sequencing of the rfa gene cluster of the LT2 strain of Salmonella typhimurium reveals a segment 336 base-pair in length between the rfaA and rfaB genes. This region corresponds to the area occupied by the rfaS gene in the K-12 strain of Escherichia coli. This segment, which is quiescent in the LT2 strain, probably contained a functional gene in the past. The lipopolysaccharide phenotype of the K-12 strain also lends support to this hypothesis.

The first three genes involved in the synthesis of the lipopolysaccharide core in Escherichia coli were identified and characterized. These genes were preliminarily identified by their complementation to rfa mutants in Salmonella typhimurium. Sequence data revealed three open reading frames corresponding rfaQ, rfaP and rfaG. In vitro synthesized proteins showed them to be basic and soluble. Sequence comparisons showed some homologies between RfaQ and RfaC and RfaF, which are involved in the synthesis of the heptose region of the core. Sequence homologies were also observed between RfaB, RfaG and RfaK, which are speculated to be hexose transferases.

The adherent-invasive Escherichia coli (AIEC) pathotype has been implicated in the pathogenesis of inflammatory bowel diseases in general and in Crohn’s disease (CD) in particular. AIEC strains are primarily characterized by their ability to adhere to and invade intestinal epithelial cells. However, the genetic and phenotypic features of AIEC isolates vary greatly as a function of the strain’s clonality, host factors, and the gut microenvironment. It is thus essential to identify the determinants of AIEC pathogenicity and understand their role in intestinal epithelial barrier dysfunction and inflammation. We reasoned that soil nematode Caenorhabditis elegans (a simple but powerful model of host-bacterium interactions) could be used to study the virulence of AIEC vs. non- AIEC E. coli strains. Indeed, we found that the colonization of C. elegans (strain N2) by E. coli impacted survival in a strain-specific manner. Moreover, the AIEC strains’ ability to invade cells in vitro was linked to the median lifespan in C. elegans (strain PX627). However, neither the E. coli intrinsic invasiveness (i.e., the fact for an individual strain to be characterized as invasive or not) nor AIEC’s virulence levels (i.e., the intensity of invasion, established in % from the infectious inoculum) in intestinal epithelial cells was correlated with C. elegans’ lifespan in the killing assay. Nevertheless, AIEC longevity of C. elegans might be a relevant model for screening anti-adhesion drugs and anti-invasive probiotics. [ABSTRACT FROM AUTHOR]

Bubonic plague (a fatal, flea-transmitted disease) remains an international public health concern. Although our understanding of the pathogenesis of bubonic plague has improved significantly over the last few decades, researchers have still not been able to define the complete set of Y. pestis genes needed for disease or to characterize the mechanisms that enable infection. Here, we generated a library of Y. pestis mutants, each lacking one or more of the genes previously identified as being up-regulated in vivo. We then screened the library for attenuated virulence in rodent models of bubonic plague. Importantly, we tested mutants both individually and using a novel, “per-pool” screening method that we have developed. Our data showed that in addition to genes involved in physiological adaption and resistance to the stress generated by the host, several previously uncharacterized genes are required for virulence. One of these genes (ympt1.66c, which encodes a putative helicase) has been acquired by horizontal gene transfer. Deletion of ympt1.66c reduced Y. pestis' ability to spread to the lymph nodes draining the dermal inoculation site – probably because loss of this gene decreased the bacteria's ability to survive inside macrophages. Our results suggest that (i) intracellular survival during the early stage of infection is important for plague and (ii) horizontal gene transfer was crucial in the acquisition of this ability. [ABSTRACT FROM AUTHOR]

The article reports on the isolation and characterization of a bacteriophage capable of mediating generalized transduction in Serratia marcescens strain Db11 by researchers from Great Britain and France. The genome of this Serratia strain has recently been sequenced and is likely a virulent phage. The phage DNA was resistant to digestion with restriction enzymes.