The host-adapted human pathogen Neisseria gonorrhoeae is the causative agent of gonorrhoea. Consistent with its proposed evolution from an ancestral commensal bacterium, N. gonorrhoeae has retained features that are common in commensals, but it has also developed unique features that are crucial to its pathogenesis. The continued worldwide incidence of gonorrhoeal infection, coupled with the rising resistance to antimicrobials and the difficulties in controlling the disease in developing countries, highlights the need to better understand the molecular basis of N. gonorrhoeae infection. This knowledge will facilitate disease prevention, surveillance and control, improve diagnostics and may help to facilitate the development of effective vaccines or new therapeutics. In this Review, we discuss sex-related symptomatic gonorrhoeal disease and provide an overview of the bacterial factors that are important for the different stages of pathogenesis, including transmission, colonization and immune evasion, and we discuss the problem of antibiotic resistance.

Animal epithelial tissue becomes reproducibly colonized by specific environmental bacteria. The bacteria (microbiota) perform critical functions for the host's tissue development, immune system development, and nutrition; yet the processes by which bacterial diversity in the environment is selected to assemble the correct communities in the host are unclear. To understand the molecular determinants of microbiota selection, we examined colonization of a simplified model in which the light organ of Euprymna scolopes squid is colonized exclusively by Vibrio fischeri bacteria. We applied highthroughput insertion sequencing to identify which bacterial genes are required during host colonization. A library of over 41,000 unique transposon insertions was analyzed before and after colonization of 1,500 squid hatchlings. Mutants that were reproducibly depleted following squid colonization represented 380 genes, including 37 that encode known colonization factors. Validation of select mutants in defined competitions against the wild-type strain identified nine mutants that exhibited a reproducible colonization defect. Some of the colonization factors identified included genes predicted to influence copper regulation and secretion. Other mutants exhibited defects in biofilm development, which is required for aggregation in host mucus and initiation of colonization. Biofilm formation in culture and in vivo was abolished in a strain lacking the cytoplasmic chaperone DnaJ, suggesting an important role for protein quality control during the elaboration of bacterial biofilm in the context of an intact host immune system. Overall these data suggest that cellular stress responses and biofilm regulation are critical processes underlying the reproducible colonization of animal hosts by specific microbial symbionts.H umans and other animals are often sterile before birth, from which point they immediately proceed to acquire environmental bacteria (1). The bacteria that reproducibly colonize animal hosts are critical for host tissue development, immune system development, and nutrient acquisition. The selection process by which the functional symbionts take residence in the animal from among the great diversity of environmental microbes is poorly understood, so model systems have been especially valuable to examine how specific patterns of colonization are shaped by the genetic makeup of the bacteria and the host environment (2).The light organ of the Hawaiian bobtail squid, Euprymna scolopes, is colonized exclusively by the Gram-negative luminous bacterium Vibrio fischeri. The host inhabits seawater containing 10 6 bacteria per milliliter, with V. fischeri comprising at most 0.02% of the environmental population (3). E. scolopes hatch without symbionts, but then rapidly acquire environmental bacteria and proceed to select for V. fischeri in a "winnowing" process that ensures colonization by only the specific symbiont (4). The squid-Vibrio system thus presents an opportunity to investigate the processes that underlie acquisition of s...

ABSTRACTMany pathogens regulate or modify their immune-stimulating ligands to avoid detection by their infected hosts.Listeria monocytogenes, a facultative intracellular bacterial pathogen, interacts with multiple components of mammalian innate immunity during its infection cycle. During replication within the cytosol of infected cells,L. monocytogenesutilizes two multidrug efflux pumps, MdrM and MdrT, to secrete the small nucleic acid second messenger cyclic-di-AMP (c-di-AMP). Host recognition of c-di-AMP triggers the production of type I interferons, including beta interferon (IFN-β), which, surprisingly, promoteL. monocytogenesvirulence. In this study, we have examined the capacity of multiple laboratory and clinical isolates ofL. monocytogenesto stimulate host production of IFN-β. We have identified theL. monocytogenesstrain LO28 as able to hyperinduce IFN-β production in infected cells ∼30-fold more than the common laboratory cloneL. monocytogenesstrain 10403S. Genomic analyses determined that LO28 contains a naturally occurring loss-of-function allele of the transcriptional regulator BrtA and correspondingly derepresses expression of MdrT. Surprisingly, while derepression of MdrT resulted in hyperstimulation of IFN-β, it results in significant attenuation in multiple mouse models of infection. While type I interferons may promoteL. monocytogenesvirulence, this study demonstrates that unregulated expression of the c-di-AMP-secreting efflux pump MdrT significantly restricts virulencein vivoby an unknown mechanism.

SummaryMammalian bile has potent anti-microbial activity, yet bacterial pathogens of the gastrointestinal tract and hepatobiliary system nonetheless persist and replicate within bile-rich environments. Listeria monocytogenes, a Gram-positive pathogen, encounters bile at three stages throughout its infectious cycle in vivo: in the gut during initial infection, in the liver where it replicates robustly and in the gallbladder, from which it can return to the intestine and thence to the environment. The mechanisms by which L. monocytogenes senses mammalian bile and counteracts its bactericidal effects are not fully understood. In this report, we have determined the L. monocytogenes bile-induced transcriptome, finding that many critical virulence factors are regulated by bile. Among these, the multidrug efflux pumps MdrM and MdrT, previously shown to be critical for the bacterial provocation of a pathogenesis-promoting host innate immune response, are robustly and specifically induced by the bile component cholic acid. This induction is mediated by BrtA, the first identified L. monocytogenes sensor of bile, which loses the ability to bind to and repress the mdrT promoter in the presence of cholic acid. We show that MdrT can export cholic acid, and that DmdrT bacteria are significantly attenuated both in vitro when exposed to cholic acid or bile, and in vivo in the gallbladders and livers of infected mice.

The strict human pathogen Neisseria gonorrhoeae is the only causative agent of the sexually transmitted disease gonorrhea. This bacterium encounters hydrogen peroxide produced from host cells during infection, but the organism survives in the presence of this antimicrobial agent. This work shows that the bacterium responds to hydrogen peroxide by regulating the expression of many genes involved in multiple processes.