LBP [LPS (lipopolysaccharide)-binding protein] and BPI (bactericidal/permeability-increasing protein) are components of the immune system that have been principally studied in mammals for their involvement in defense against bacterial pathogens. These proteins share a basic architecture and residues involved in LPS binding. Putative orthologues, i.e., proteins encoded by similar genes that diverged from a common ancestor, have been found in a number of non-mammalian vertebrate species and several non-vertebrates. Similar to other aspects of immunity, such as the activity of Toll-like receptors and NOD (nucleotide-binding oligomerization domain) proteins, analysis of the conservation of LBPs and BPIs in the invertebrates promises to provide insight into features essential to the form and function of these molecules. This review considers state-of-the-art knowledge in the diversity of the LBP/BPI proteins across the eukaryotes and also considers their role in mutualistic symbioses. Recent studies of the LBPs and BPIs in an invertebrate model of beneficial associations, the Hawaiian bobtail squid Euprymna scolopes’ alliance with the marine luminous bacterium Vibrio fischeri, are discussed as an example of the use of non-vertebrate models for the study of LBPs and BPIs.

Bacterial flagella mediate host–microbe interactions through tissue tropism during colonization, as well as by activating immune responses. The flagellar shaft of some bacteria, including several human pathogens, is encased in a membranous sheath of unknown function. While it has been hypothesized that the sheath may allow these bacteria to evade host responses to the immunogenic flagellin subunit, this unusual structural feature has remained an enigma. Here we demonstrate that the rotation of the sheathed flagellum in both the mutualist Vibrio fischeri and the pathogen Vibrio cholerae promotes release of a potent bacteria-derived immunogen, lipopolysaccharide, found in the flagellar sheath. We further present a new role for the flagellar sheath in triggering, rather than circumventing, host immune responses in the model squid-vibrio symbiosis. Such an observation not only has implications for the study of bacterial pathogens with sheathed flagella, but also raises important biophysical questions of sheathed-flagellum function.DOI: http://dx.doi.org/10.7554/eLife.01579.001

Background:The structure and function of the Vibrio fischeri O-antigen were unknown. Results: The O-antigen structure was determined using an O-antigen ligase mutant. Conclusion: This mutant had a motility defect, and comparison of its LPS with wild-type LPS showed that the O-antigen contains some unusual sugars. Significance: The O-antigen mutation results in a significantly slower rate of bacterial colonization of the squid light organ.

We characterized bactericidal permeability-increasing proteins (BPIs) of the squid Euprymna scolopes, EsBPI2 and EsBPI4. They have molecular characteristics typical of other animal BPIs, are closely related to one another, and nest phylogenetically among invertebrate BPIs. Purified EsBPIs had antimicrobial activity against the squid’s symbiont, Vibrio fischeri, which colonizes light organ crypt epithelia. Activity of both proteins was abrogated by heat treatment and coincubation with specific antibodies. Pretreatment under acidic conditions similar to those during symbiosis initiation rendered V. fischeri more resistant to the antimicrobial activity of the proteins. Immunocytochemistry localized EsBPIs to the symbiotic organ and other epithelial surfaces interacting with ambient seawater. The proteins differed in intracellular distribution. Further, whereas EsBPI4 was restricted to epithelia, EsBPI2 also occurred in blood and in a transient juvenile organ that mediates hatching. The data provide evidence that these BPIs play different defensive roles early in the life of E. scolopes, modulating interactions with the symbiont.

OBJECTIVE To identify facilitators and barriers to implementation of a Clostridium difficile screening intervention among bone marrow transplant (BMT) patients and to evaluate the clinical effectiveness of the intervention on the rate of hospital-onset C. difficile infection (HO-CDI). DESIGN Before-and-after trial SETTING A 505-bed tertiary-care medical center PARTICIPANTS All 5,357 patients admitted to the BMT and general medicine wards from January 2014 to February 2017 were included in the study. Interview participants included 3 physicians, 4 nurses, and 4 administrators. INTERVENTION All BMT patients were screened within 48 hours of admission. Colonized patients, as defined by a C. difficile-positive polymerase chain reaction (PCR) stool result, were placed under contact precautions for the duration of their hospital stay. METHODS Interview responses were coded according to the Systems Engineering Initiative for Patient Safety conceptual framework. We compared pre- and postintervention HO-CDI rates on BMT and general internal medicine units using time-series analysis. RESULTS Stakeholder engagement, at both the person and organizational level, facilitates standardization and optimization of intervention protocols. While the screening intervention was generally well received, tools and technology were sources of concern. The mean incidence of HO-CDI decreased on the BMT service postintervention (P<.0001). However, the effect of the change in the trend postintervention was not significantly different on BMT compared to the control wards (P=.93). CONCLUSIONS We report the first mixed-methods study to evaluate a C. difficile screening intervention among the BMT population. The positive nature by which the intervention was received by front-line clinical staff, laboratory staff, and administrators is promising for future implementation studies. Infect Control Hosp Epidemiol 2018;39:177-185.

Mammalian lipopolysaccharide (LPS) binding proteins (LBPs) occur mainly in extracellular fluids and promote LPS delivery to specific host cell receptors. The function of LBPs has been studied principally in the context of host defense; the possible role of LBPs in nonpathogenic host-microbe interactions has not been well characterized. Using the Euprymna scolopes-Vibrio fischeri model, we analyzed the structure and function of an LBP family protein, E. scolopes LBP1 (EsLBP1), and provide evidence for its role in triggering a symbiont-induced host developmental program. Previous studies showed that, during initial host colonization, the LPS of V. fischeri synergizes with peptidoglycan (PGN) monomer to induce morphogenesis of epithelial tissues of the host animal. Computationally modeled EsLBP1 shares some but not all structural features of mammalian LBPs that are thought important for LPS binding. Similar to human LBP, recombinant EsLBP1 expressed in insect cells bound V. fischeri LPS and Neisseria meningitidis lipooligosaccharide (LOS) with nanomolar or greater affinity but bound Francisella tularensis LPS only weakly and did not bind PGN monomer. Unlike human LBP, EsLBP1 did not bind N. meningitidis LOS:CD14 complexes. The eslbp1 transcript was upregulated ~22-fold by V. fischeri at 24 h postinoculation. Surprisingly, this upregulation was not induced by exposure to LPS but, rather, to the PGN monomer alone. Hybridization chain reaction-fluorescent in situ hybridization (HCR-FISH) and immunocytochemistry (ICC) localized eslbp1 transcript and protein in crypt epithelia, where V. fischeri induces morphogenesis. The data presented here provide a window into the evolution of LBPs and the scope of their roles in animal symbioses.

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