SummaryWzz proteins regulate the degree of polymerization of the O antigen (Oag) subunits in lipopolysaccharide (LPS) biosynthesis. Although the pathogenic relevance of Oag is well recognized, the significance of Oag chain length regulation is not well defined. In this report, Salmonella typhimurium was shown to possess two functional wzz genes resulting in a bimodal Oag length distribution. In addition to the previously described wzz ST that results in long (L) modal length LPS with 16-35 Oag repeat units (RUs), we now report that wzz fepE , a homologue of Escherichia coli fepE , is responsible for the production of very long (VL) modal length LPS Oag, estimated to contain > 100 Oag RUs. Analysis of a series of isogenic S. typhimurium C5 mutants found that the presence of either wzz gene (and hence either modal length) was sufficient for complement resistance and virulence in the mouse model of infection, suggesting a degree of redundancy in the role of these two wzz genes and their respective Oag modal lengths. In contrast, the wzz ST / wzz fepE double mutant, with relatively short, random-length Oag, displayed enhanced susceptibility to complement and was highly attenuated in the mouse. This clearly demonstrates the molecular genetic basis for the longer LPS Oag chains previously identified as the basis of complement resistance in Salmonella . The presence of wzz fepE homologues in the genomic sequences of strains of Escherichia coli , Shigella flexneri and multiple serovars of Salmonella suggests that bimodality of LPS Oag is a common phenomenon in the Enterobacteriaceae.

Background: We summarised data from studies reporting on macrolide and fluoroquinolone resistanceassociated mutations in Mycoplasma genitalium, examined temporal trends, and associations with geographical location, sex and population.

Leptospira interrogans is the most common cause of leptospirosis in humans and animals. Genetic analysis of L. interrogans has been severely hindered by a lack of tools for genetic manipulation. Recently we developed the mariner-based transposon Himar1 to generate the first defined mutants in L. interrogans. In this study, a total of 929 independent transposon mutants were obtained and the location of insertion determined. Of these mutants, 721 were located in the protein coding regions of 551 different genes. While sequence analysis of transposon insertion sites indicated that transposition occurred in an essentially random fashion in the genome, 25 unique transposon mutants were found to exhibit insertions into genes encoding 16S or 23S rRNAs, suggesting these genes are insertional hot spots in the L. interrogans genome. In contrast, loci containing notionally essential genes involved in lipopolysaccharide and heme biosynthesis showed few transposon insertions. The effect of gene disruption on the virulence of a selected set of defined mutants was investigated using the hamster model of leptospirosis. Two attenuated mutants with disruptions in hypothetical genes were identified, thus validating the use of transposon mutagenesis for the identification of novel virulence factors in L. interrogans. This library provides a valuable resource for the study of gene function in L. interrogans. Combined with the genome sequences of L. interrogans, this provides an opportunity to investigate genes that contribute to pathogenesis and will provide a better understanding of the biology of L. interrogans.Leptospira interrogans is a spirochete that is the main causative agent of leptospirosis. This zoonosis has emerged as a major public health problem in much of the developing world, with more than 500,000 cases of severe leptospirosis reported each year, for which the mortality rate is more than 10% (17).The genus Leptospira is composed of both saprophytic and pathogenic species. The genome sequences of two epidemic strains of L. interrogans serovars Lai and Copenhageni have been determined (20,25). More recently a human and an animal L. borgpetersenii isolate were sequenced (3), and this year, we determined the genome sequence of the saprophyte L. biflexa (22). The resulting sequences provide an invaluable source of information for identification of genetic determinants involved in the pathogenicity and environmental biology of the organism. For example, the host-adapted L. borgpetersenii genome is 16% smaller and has many more pseudogenes than the L. interrogans genome. These findings suggest that genome reduction has resulted in a reduced environmental transmission potential (3). L. interrogans has 627 genes that are absent in the L. biflexa genome, and more than 500 of these genes have unknown functions, suggesting the presence of novel virulence mechanisms (22). However, the lack of tools for L. interrogans genetics has hindered elucidation of the role of these genes in pathogenesis.Pathogenic leptospires are difficult...

In the context of high levels of antimicrobial resistance, switching from azithromycin to doxycycline for presumptive treatment of M. genitalium, followed by resistance-guided therapy, cured ≥92% of infections, with infrequent selection of macrolide resistance.