Comprehensive Sterilization of Malaria Vectors Using Pyriproxyfen: A Step Closer to Malaria Elimination

One of the main challenges to malaria elimination is the resilience of vectors, such as Anopheles arabiensis, that evade lethal exposure to insecticidal control measures or express resistance to their active ingredients. This study investigated a novel technology for population control that sterilizes mosquitoes using pyriproxyfen, a juvenile hormone analogue. Females of An. arabiensis were released in a semifield system divided into four equal sections, and each section had a mud hut sheltering a tethered cow providing a blood source for mosquitoes. In all sections, the inner mud hut walls and roofs were lined with black cotton cloth. In one-half of the sections, the cloth was dusted with pyriproxyfen. An overwhelming 96% reduction in adult production was achieved in pyriproxyfen-treated sections compared with control sections. This unprecedented level of control can be exploited to design new vector control strategies that particularly target existing behaviorally resilient and insecticide-resistant populations.     

Quantifying the atomic-level mechanics of single long physisorbed molecular chains

Individual in situ polymerized fluorene chains 10–100 nm long linked by C–C bonds are pulled vertically from an Au(111) substrate by the tip of a low-temperature atomic force microscope. The conformation of the selected chains is imaged before and after manipulation using scanning tunneling microscopy. The measured force gradient shows strong and periodic variations that correspond to the step-by-step detachment of individual fluorene repeat units. These variations persist at constant intensity until the entire polymer is completely removed from the surface. Calculations based on an extended Frenkel–Kontorova model reproduce the periodicity and magnitude of these features and allow us to relate them to the detachment force and desorption energy of the repeat units. The adsorbed part of the polymer slides easily along the surface during the pulling process, leading to only small oscillations as a result of the high stiffness of the fluorenes and of their length mismatch with respect to the substrate surface structure. A significant lateral force also is caused by the sequential detachment of individual units. The gained insight into the molecule–surface interactions during sliding and pulling should aid the design of mechanoresponsive nanosystems and devices.Ever since the invention of the atomic force microscope (AFM) (1) and the first imaging applications, force spectroscopy has been applied to study the mechanical behavior of polymers (2); more complex chain-like biomolecules, e.g., DNA complementary strands (3); and proteins, subject to controlled extension (2) or applied force (4), mostly in solution and at room temperature. Reactive groups are chemically inserted at the ends and/or along each molecule to firmly bind some of them to suitably functionalized tips and sample surfaces. Irreversible jumps in curves of force vs. vertical separation may be associated in this way with the rupture of bonds or the unfolding of coiled subunits. If reproducible, the lowest peak in the histogram of the forces attained just before each jump is attributed to such an event in a single molecular chain or complementary pair. In the case of homogeneous polymers or protein segments, simulations based on two-state rate theory combined with a standard model of polymer nonlinear elasticity can reproduce such events, whereas reversible plateaus or continuous rises in the force may be associated with fast binding–rebinding processes or with large thermal fluctuations (2). Attention thus has focused on conformational changes strongly influenced by pulling speed or imposed force jumps (4) and also by external stimuli, e.g., optical excitation of inserted chromophores (5) or specific reactants or enzymes (6). Furthermore, mechanical forces recently were discovered by chemists as a unique stimulus to induce specific chemical reactions. In this so-called mechanochemistry, sonication typically is applied to polymer systems and is believed to result in a strong force acting on the weakest link in the chain, where the reaction takes place (7, 8). Regardless of the direct or indirect exposure to force, it is clear that the mechanics of polymer chains constrained in their surrounding environment is of utmost importance for a variety of biophysical and chemical processes as well as self-healing materials applications (9, 10).A few pulling studies have been conducted on polyelectrolytes unspecifically adsorbed on self-assembled monolayers via tunable electrostatic interactions (11), including DNA (12). They merely revealed noisy force plateaus, interpreted as continuous partial desorption of single chains, terminated by a drop to zero upon complete detachment from the surface. Despite the undisputed merit of these studies, little is known about the mechanical behavior of single molecular chains pulled off a surface, both defined and characterized on the atomic scale, in the absence of significant thermal fluctuations and drifts. Measurements at low temperature reduce the diffusion of adsorbates and provide an opportunity to determine the energetic landscape of specific molecules interacting with a surface under controlled conditions. As demonstrated here, the sliding and detachment mechanisms of individual polymer repeat units can then be inferred from the analysis of pulling experiments. A detailed interpretation of our results, based on a modified Frenkel–Kontorova (FK) model (13), also is presented.     

Diagnosis and non‐surgical treatment of peri‐implant diseases and maintenance care of patients with dental implants – Consensus report of working group 3

The following consensus report is based on four background reviews. The frequency of maintenance visits is based on patient risk indicators, homecare compliance and prosthetic design. Generally, a 6‐month visit interval or shorter is preferred. At these visits, peri‐implant probing, assessment of bleeding on probing and, if warranted, a radiographic examination is performed. Diagnosis of peri‐implant mucositis requires: (i) bleeding or suppuration on gentle probing with or without increased probing depth compared with previous examinations; and (ii) no bone loss beyond crestal bone level changes resulting from initial bone remodelling. Diagnosis of peri‐implantitis requires: (i) bleeding and/or suppuration on gentle probing; (ii) an increased probing depth compared with previous examinations; and (iii) bone loss beyond crestal bone level changes resulting from initial bone remodelling. If diagnosis of disease is established, the inflammation should be resolved. Non‐surgical therapy is always the first choice. Access and motivation for optimal oral hygiene are key. The patient should have a course of mechanical therapy and, if a smoker, be encouraged not to smoke. Non‐surgical mechanical therapy and oral hygiene reinforcement are useful in treating peri‐implant mucositis. Power‐driven subgingival air‐polishing devices, Er: YAG lasers, metal curettes or ultrasonic curettes with or without plastic sleeves can be used to treat peri‐implantitis. Such treatment usually provides clinical improvements such as reduced bleeding tendency, and in some cases a pocket‐depth reduction of ≤ 1 mm. In advanced cases, however, complete resolution of the disease is unlikely.     

Microbial-induced meprin β cleavage in MUC2 mucin and a functional CFTR channel are required to release anchored small intestinal mucus

The mucus that covers and protects the epithelium of the intestine is built around its major structural component, the gel-forming MUC2 mucin. The gel-forming mucins have traditionally been assumed to be secreted as nonattached. The colon has a two-layered mucus system where the inner mucus is attached to the epithelium, whereas the small intestine normally has a nonattached mucus. However, the mucus of the small intestine of meprin β-deficient mice was now found to be attached. Meprin β is an endogenous zinc-dependent metalloprotease now shown to cleave the N-terminal region of the MUC2 mucin at two specific sites. When recombinant meprin β was added to the attached mucus of meprin β-deficient mice, the mucus was detached from the epithelium. Similar to meprin β-deficient mice, germ-free mice have attached mucus as they did not shed the membrane-anchored meprin β into the luminal mucus. The ileal mucus of cystic fibrosis (CF) mice with a nonfunctional cystic fibrosis transmembrane conductance regulator (CFTR) channel was recently shown to be attached to the epithelium. Addition of recombinant meprin β to CF mucus did not release the mucus, but further addition of bicarbonate rendered the CF mucus normal, suggesting that MUC2 unfolding exposed the meprin β cleavage sites. Mucus is thus secreted attached to the goblet cells and requires an enzyme, meprin β in the small intestine, to be detached and released into the intestinal lumen. This process regulates mucus properties, can be triggered by bacterial contact, and is nonfunctional in CF due to poor mucin unfolding.The gastrointestinal (GI) tract is protected from self-digestion and microbiota by mucus (1). This mucus is differently organized throughout the GI tract: the stomach and colon have a two-layered mucus system with an inner mucus layer attached to the epithelium and formed by stratified mucin sheets (2). This layer is 50–200 µm thick and impenetrable for bacteria, is constantly renewed by secreted mucins from the goblet cells, and further toward the lumen proteolytically converted into a nonattached and less dense outer mucus layer. This outer layer is the habitat and nutritional source for the commensal bacteria (2). In contrast, the small intestine has only one single mucus type that is not attached to the epithelium (3).The main structural component of the intestinal mucus is the heavily glycosylated polymeric MUC2 mucin which is densely packed inside the goblet cell and after secretion and a 1,000-fold expansion forms flat, net-like structures stacked into stratified mucin sheets in the colon (4). The same MUC2 mucin is processed differently in the small intestine where it appeared less organized but still filled the space between villi (3). This mucus was easily aspirated and penetrable to beads the size of bacteria (3). Bacteria could penetrate, but still the space between the villi was kept free of bacteria in the small intestine due to effective intestinal peristalsis, fast mucus renewal, and a high concentration of antibacterial peptides and proteins (3, 5). In fact, the structure of the small intestinal mucus as a nonattached and less organized layer mimics the situation for the outer colon mucus layer that has been shown to be generated from the inner mucus layer by proteolytic processing of the MUC2 mucin (2).Meprins are zinc-dependent metalloendopeptidases and belong to the astacin family (6). They comprise two homologous enzymes, meprin α and meprin β, where meprin α is the secreted and meprin β the membrane-tethered variant. They can form heterodimers (meprin α and β), homodimers (meprin β), and large oligomers (meprin α), forming one of the largest secreted protease complexes known. Although both enzymes share a common domain structure, they exhibit distinct features in substrate recognition and cleavage specificities. The enzymes can hydrolyze a broad variety of substrates, such as growth factors, peptide hormones, or compounds of the extracellular matrix like procollagen III, fibronectin, and tenascin-C (7–9). The meprin β enzyme is highly expressed in the enterocytes of the small intestine and is thereby localized close to the mucin networks (10).Cystic fibrosis (CF) is a severe disease that affects most of the mucus-producing organs of the body (11). The disease is caused by a nonfunctional cystic fibrosis transmembrane conductance regulator (CFTR) channel that normally mediates passive transport of chloride and bicarbonate ions (12, 13). Although a majority of the clinical CF symptoms can be attributed to stagnant mucus, the more precise link between the lack of CFTR function and mucus properties has been difficult to understand. We recently showed that the small intestinal mucus of CF mice, in contrast to the WT, was attached to the epithelium and impossible to aspirate (14). Although CF mice have only minor lung problems, their intestinal phenotype is similar to the human disease characterized by meconium ileus and distal intestinal obstruction syndrome (DIOS). When the CF mucus was secreted into a solution of ∼100 mM bicarbonate, the mucus was released from its attachment. Mucins are densely packed in the goblet cell granulae due to Ca²⁺ ions and low pH, and the role of bicarbonate is to remove the Ca²⁺ ions and increase the pH to allow for the >1,000-fold mucin expansion (4). When already formed mucus was treated with bicarbonate, the mucus was normalized and possible to aspirate, although its increased mucin density remained largely unaltered (14). This suggested that mucin attachment and expansion might be different phenomena and made us analyze this further.We have now found that meprin β is able to cleave the MUC2 mucin N terminus and that this is involved in the detachment of the mucus of the small intestine in a process controlled by bacteria and a functional CFTR channel. We thus describe a fundamental constitutive mechanism which involves an endogenous protease acting on the mucus network to alter its attached properties.     

PER extended-spectrum β-lactamases originate from Pararheinheimera spp

To investigate the origin of PER extended-spectrum β-lactamases, publicly available sequence databases were searched for bla_PER-like genes. Three genomes from Pararheinheimera, a genus associated with water and soil environments, were found to carry bla_PER-like genes but lacked the ISCR1/ISPa12/ISPa13 insertion sequences commonly associated with bla_PER in clinical isolates. Sequence analysis revealed 78–96% nucleotide identity and conserved synteny between the clinical mobile genetic elements (MGEs) encoding bla_PER-1 and the bla_PER locus in the Pararheinheimera genomes. Notably, bla_PER genes were only identified in 3 of 21 Pararheinheimera and Rheinheimera genomes, whereas the genetic environment of bla_PER genes as found in clinical MGEs was conserved in all Pararheinheimera and Rheinheimera genomes. These findings indicate that bla_PER genes were likely acquired by a branch of the Pararheinheimera genus long before the antibiotic era. Later, bla_PER genes were mobilised, likely through the involvement of insertion sequences, from one or several Pararheinheimera species, allowing their dissemination into human pathogens.