Oxygen as a Virulence Determinant in Polymicrobial Infections

Infections caused by multiple organisms, or polymicrobial infections, are likely more common than is broadly appreciated. Interaction among microbial communities (and with their host) can change the infection landscape by subverting immunity, providing nutrients and inhibiting competing microbes. Stacy et al. (A. Stacy, D. Fleming, R. J. Lamont, K. P. Rumbaugh, and M. Whiteley, mBio 7:e00782-16, 2016, http://dx.doi.org/10.1128/mBio.00782-16) described a novel mechanism that results in synergistic growth of oral microbes Aggregatibacter actinomycetemcomitans and Streptococcus gordonii. The authors used whole-genome fitness profiling by transposon sequencing (Tn-seq) to identify genes differentially required for growth in vitro versus in a mono- or coinfection in a thigh abscess model. They found that coinfection with S. gordonii allowed A. actinomycetemcomitans to shift from an anaerobic to an aerobic mode of growth. This shift involved the production of a terminal electron acceptor H2O2 by S. gordonii and increased A. actinomycetemcomitans persistence—an interaction termed “cross-respiration.

The Long-Term Impact of Physical and Emotional Trauma: The Station Nightclub Fire

Background: Survivors of physical and emotional trauma experience enduring occupational, psychological and quality of life impairments. Examining survivors from a large fire provides a unique opportunity to distinguish the impact of physical and emotional trauma on long-term outcomes. The objective is to detail the multi-dimensional long-term effects of a large fire on its survivor population and assess differences in outcomes between survivors with and without physical injury. Methods and Findings: This is a survey-based cross-sectional study of survivors of The Station fire on February 20, 2003. The relationships between functional outcomes and physical injury were evaluated with multivariate regression models adjusted for pre-injury characteristics and post-injury outcomes. Outcome measures include quality of life (Burn Specific Health Scale–Brief), employment (time off work), post-traumatic stress symptoms (Impact of Event Scale–Revised) and depression symptoms (Beck Depression Inventory). 104 fire survivors completed the survey; 47% experienced a burn injury. There was a 42% to 72% response rate range. Although depression and quality of life were associated with burn injury in univariate analyses (p<0.05), adjusted analyses showed no significant relationship between burn injury and these outcomes (p = 0.91; p = .51). Post-traumatic stress symptoms were not associated with burn injury in the univariate (p = 0.13) or adjusted analyses (p = 0.79). Time off work was the only outcome in which physical injury remained significant in the multivariate analysis (p = 0.03). Conclusions: Survivors of this large fire experienced significant life disruption, including occupational, psychological and quality of life sequelae. The findings suggest that quality of life, depression and post-traumatic stress outcomes are related to emotional trauma, not physical injury. However, physical injury is correlated with employment outcomes. The long-term impact of this traumatic event underscores the importance of longitudinal and mental health care for trauma survivors, with attention to those with and without physical injuries

A noncanonical autophagy pathway restricts Toxoplasma gondii growth in a strain-specific manner in IFN-γ-activated human cells

ABSTRACT A core set of autophagy proteins is required for gamma interferon (IFN-γ)-mediated clearance of Toxoplasma gondii in the mouse because of their control of several downstream effectors, including immunity-related GTPases (IRGs) and guanylate-binding proteins (GBPs). However, these effectors are absent (i.e., IRGs) from or nonessential (i.e., GBPs) in IFN-γ-activated human cells, raising the question of how these cells control parasite replication. Here, we define a novel role for ubiquitination and recruitment of autophagy adaptors in the strain-specific control of T. gondii replication in IFN-γ-activated human cells. Vacuoles containing susceptible strains of T. gondii became ubiquitinated, recruited the adaptors p62 and NDP52, and were decorated with LC3. Parasites within LC3-positive vacuoles became enclosed in multiple layers of host membranes, resulting in stunting of parasite replication. However, LC3-positive T. gondii-containing vacuoles did not fuse with endosomes and lysosomes, indicating that this process is fundamentally different from xenophagy, a form of autophagy involved in the control of intracellular bacterial pathogens. Genetic knockout of ATG16L or ATG7 reverted the membrane encapsulation and restored parasite replication, indicating that core autophagy proteins involved in LC3 conjugation are important in the control of parasite growth. Despite a role for the core autophagy machinery in this process, upstream activation through Beclin 1 was not sufficient to enhance the ubiquitination of T. gondii-containing vacuoles, suggesting a lack of reliance on canonical autophagy. These findings demonstrate a new mechanism for IFN-γ-dependent control of T. gondii in human cells that depends on ubiquitination and core autophagy proteins that mediate membrane engulfment and restricted growth

Parasite fate and involvement of infected cells in the induction of CD4+ and CD8+ T cell responses to Toxoplasma gondii

During infection with the intracellular parasite Toxoplasma gondii, the presentation of parasite-derived antigens to CD4+ and CD8+ T cells is essential for long-term resistance to this pathogen. Fundamental questions remain regarding the roles of phagocytosis and active invasion in the events that lead to the processing and presentation of parasite antigens. To understand the most proximal events in this process, an attenuated non-replicating strain of T. gondii (the cpsII strain) was combined with a cytometry-based approach to distinguish active invasion from phagocytic uptake. In vivo studies revealed that T. gondii disproportionately infected dendritic cells and macrophages, and that infected dendritic cells and macrophages displayed an activated phenotype characterized by enhanced levels of CD86 compared to cells that had phagocytosed the parasite, thus suggesting a role for these cells in priming naïve T cells. Indeed, dendritic cells were required for optimal CD4+ and CD8+ T cell responses, and the phagocytosis of heat-killed or invasion-blocked parasites was not sufficient to induce T cell responses. Rather, the selective transfer of cpsII-infected dendritic cells or macrophages (but not those that had phagocytosed the parasite) to naïve mice potently induced CD4+ and CD8+ T cell responses, and conferred protection against challenge with virulent T. gondii. Collectively, these results point toward a critical role for actively infected host cells in initiating T. gondii-specific CD4+ and CD8+ T cell responses

Outcomes of study participants.

<p>Outcomes of study participants.</p

Frameshift Mutations in a Single Novel Virulence Factor Alter the In Vivo Pathogenicity of Chlamydia trachomatis for the Female Murine Genital Tract▿ ¶ ‖

Chlamydia trachomatis is a human pathogen of global importance. An obstacle to studying the pathophysiology of human chlamydial disease is the lack of a suitable murine model of C. trachomatis infection. Mice are less susceptible to infection with human isolates due in part to innate mouse-specific host defense mechanisms to which human strains are sensitive. Another possible factor that influences the susceptibility of mice to infection is that human isolates are commonly cultivated in vitro prior to infection of mice; therefore, virulence genes could be lost as a consequence of negative selective pressure. We tested this hypothesis by infecting innate immunity-deficient C3H/HeJ female mice intravaginally with a human serovar D urogenital isolate that had undergone multiple in vitro passages. We observed early and late infection clearance phenotypes. Strains of each phenotype were isolated and then used to reinfect naïve mice. Following infection, the late-clearance strain was significantly more virulent. It caused unvarying infections of much longer durations with greater infectious burdens that naturally ascended to the upper genital tract, causing salpingitis. Despite contrasting in vivo virulence characteristics, the strains exhibited no differences in the results of in vitro infectivity assays or sensitivities to gamma interferon. Genome sequencing of the strains revealed mutations that localized to a single gene (CT135), implicating it as a critical virulence factor. Mutations in CT135 were not unique to serovar D but were also found in multiple oculogenital reference strains. Our findings provide new information about the pathogenomics of chlamydial infection and insights for improving murine models of infection using human strains

Survey variables.

<p>Survey variables.</p

Univariate and multivariate analyses of outcomes.

a<p>In the univariate analysis an empty cell occurs because the logistic regression analysis for the binary outcome employment does not produce a constant. In the multivariate analysis empty cells occur where the outcome and variable are the same.</p

Guanylate-binding Protein 1 (Gbp1) Contributes to Cell-autonomous Immunity against <i>Toxoplasma gondii</i>

<div><p>IFN-γ activates cells to restrict intracellular pathogens by upregulating cellular effectors including the p65 family of guanylate-binding proteins (GBPs). Here we test the role of Gbp1 in the IFN-γ-dependent control of <i>T. gondii</i> in the mouse model. Virulent strains of <i>T. gondii</i> avoided recruitment of Gbp1 to the parasitophorous vacuole in a strain-dependent manner that was mediated by the parasite virulence factors ROP18, an active serine/threonine kinase, and the pseudokinase ROP5. Increased recruitment of Gbp1 to Δ<i>rop18</i> or Δ<i>rop5</i> parasites was associated with clearance in IFN-γ-activated macrophages <i>in vitro</i>, a process dependent on the autophagy protein Atg5. The increased susceptibility of Δ<i>rop18</i> mutants in IFN-γ-activated macrophages was reverted in Gbp1^−/− cells, and decreased virulence of this mutant was compensated in Gbp1^−/− mice, which were also more susceptible to challenge with type II strain parasites of intermediate virulence. These findings demonstrate that Gbp1 plays an important role in the IFN-γ-dependent, cell-autonomous control of toxoplasmosis and predict a broader role for this protein in host defense.</p></div