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Multi-drug resistant (MDR), gram-negative Enterobacteriaceae, such as Escherichia coli (E. coli) limit therapeutic options and increase morbidity, mortality, and treatment costs worldwide. They pose a serious burden on healthcare systems, especially in developing countries like Rwanda. Several studies have shown the effects caused by the global spread of extended-spectrum beta-lactamase (ESBL)-producing E. coli. However, limited data is available on transmission dynamics of these pathogens and the mobile elements they carry in the context of clinical and community locations in Sub-Saharan Africa. Here, we examined 120 ESBL-producing E. coli strains from patients hospitalized in the University Teaching Hospital of Butare (Rwanda), their attending caregivers as well as associated community members and livestock. Based on whole-genome analysis, the genetic diversification and phylogenetics were assessed. Moreover, the content of carried plasmids was characterized and investigated for putative transmission among strains, and for their potential role as drivers for the spread of antibiotic resistance. We show that among the 30 different sequence types (ST) detected were the pandemic clonal lineages ST131, ST648 and ST410, which combine high-level antimicrobial resistance with virulence. In addition to the frequently found resistance genes blaCTX–M–15, tet(34), and aph(6)-Id, we identified csg genes, which are required for curli fiber synthesis and thus biofilm formation. Numerous strains harbored multiple virulence-associated genes (VAGs) including pap (P fimbriae adhesion cluster), fim (type I fimbriae) and chu (Chu heme uptake system). Furthermore, we found phylogenetic relationships among strains from patients and their caregivers or related community members and animals, which indicates transmission of pathogens. Also, we demonstrated the presence and potential transfer of identical/similar ESBL-plasmids in different strains from the Rwandan setting and when compared to an external plasmid. This study highlights the circulation of clinically relevant, pathogenic ESBL-producing E. coli among patients, caregivers and the community in Rwanda. Combining antimicrobial resistance with virulence in addition to the putative exchange of mobile genetic elements among bacterial pathogens poses a significant risk around the world.
Streptococcus pneumoniae (pneumococci), a human pathobiont, express and expose several proteinaceous colonization and virulence factors on its surface to facilitate on the one hand colonization of the upper respiratory tract and on the other hand pathogenesis in the host. In this study the interaction of two of such factors referred to as pneumococcal virulence factor A (PavA) and pneumococcal virulence factor B (PavB) and acting as microbial surface components recognizing adhesive matrix molecules (MSCRAMMs), was delineated with the two host matricellular proteins fibronectin (Fn) and vitronectin (Vn). Despite similarity in nomenclature, PavA and PavB represent two diverse pneumococcal proteins with respect to their structure and association with the pneumococcal surface. PavA is a non-classical surface protein (NCSP) with an ambiguous mode of secretion and anchorage while PavB is a characteristic MSCRAMM, anchored via sortase A to pneumococcal peptidoglycan. PavB has a signature of repetitive modules termed as streptococcal surface repeats (SSURE). Pneumococci preferentially interact with immobilized human Fn. In vitro cell culture adherence assays demonstrated that cell bound Fn facilitates the adherence of pneumococci to the host cells and this particular interaction is indifferent to host cell type and is species non-specific. Flow cytometry and immunoblot analyses further indicated the ability of pneumococci to interact with the soluble form of Fn in a dose-dependent but species non-specific manner. The molecular interaction of PavA and PavB (via its SSURE domains) with Fn was delineated further in detail via several direct protein-protein interaction approaches. Ligand overlay assays, surface plasmon resonance studies and SPOT peptide arrays demonstrated that PavA and PavB target at least 13 out of the 15 type III fibronectin domains located in the C-terminal part of Fn. Strikingly, both pneumococcal fibronectin-binding proteins (FnBPs) recognize similar peptides in targeted type III repeats. Structural comparisons revealed that the targeted type III epitopes cluster on the inner strands of both β-sheets forming the fibronectin domains. Importantly, synthetic peptides of FnIII1, FnIII5 or FnIII15 bind directly to FnBPs PavA and PavB, respectively. Thus, analysis of interaction of pneumococcal FnBPs PavA and PavB revealed a probable conserved and/or common pattern of molecular interaction with human Fn. In addition to Fn, pneumococcal PavB interacts with other host matricellular proteins such as human plasminogen (Plg) and human thrombospondin-1 (hTSP-1). Pneumococcal proteins such as PspC and PspC-like Hic have earlier been demonstrated to interact with hTSP-1 as well as human Vn, thereby depicting a redundant function as MSCRAMMs. In this study the role of PavB as a pneumococcal vitronectin binding protein (VnBP) was assessed. Flow cytometric analysis suggested PavB as VnBP, because strains deficient for PavB exhibited a significantly decreased ability to acquire vitronectin compared to wild-type pneumococci. When using a double knockout, deficient in expression of PavB and the VnBP PspC, the pneumococcal interaction with vitronectin was completely abolished. The direct protein-protein interaction assays such as far western ligand overlay, ELISA, and surface plasmon resonance indicated the interaction of SSURE domains with both soluble and immobilized Vn. However, the binding activity depends on the number of SSURE domains with five SSURE showing the highest binding activity to Vn. The interaction of PavB with Vn was charge dependent and heparin sensitive as analyzed by ELISA. The importance of the heparin binding domains of Vn in this interaction was further analyzed via direct protein-protein interaction approaches. Binding studies (far western ligand overlay, ELISA, and surface plasmon resonance) with truncated recombinant Vn fragments indicated that PavB targets the C-terminal heparin-binding domain (HBD3) of vitronectin, a characteristic shared with PspC, hence, suggesting a conserved molecular interaction of pneumococci with Vn. In addition to its function as an MSCRAMM, PavB has the capability to interact directly with host epithelial cells via an unknown cellular receptor. Thus, this study aimed to identify cellular receptor(s) for PavB. In vitro cell culture adherence and invasion assays confirmed that pneumococcal PavB is involved in promoting pneumococcal adherence to respiratory epithelial cells without employing any molecular bridge. The direct interaction between PavB and host epithelial cells was further confirmed via direct binding assays when using Cy5-labeled PavB and flow cytometric analysis. Strikingly, exogenously added human vitronectin competitively inhibited binding of PavB to respiratory epithelial cells. This observation led us to hypothesize that the major vitronectin receptor αvβ3 integrin acts as a potential receptor for PavB. This hypothesis was supported by functional blocking assays with monoclonal antibodies recognizing specific integrin subunits. The results revealed reduced binding of PavB in the presence of bound antibodies recognizing αv integrin indicating that PavB employs αvβ3 integrin as its direct receptor on eukaryotic cells. This was further confirmed via a direct binding assay of PavB to mouse embryonic fibroblasts (MEFs) where cells lacking αvβ3 demonstrated a marked decrease in binding to PavB. Although functional blocking assay and direct binding assay with MEFs supported the role of αvβ3 integrin as a direct adhesin for PavB, RNA interference of αv integrin in epithelial cells did not impair the binding of PavB in αv-knocked down cells in comparison to non-transfected cells. Finally, surface plasmon resonance (SPR) analysis indicated the direct interaction between pneumococcal PavB and recombinant αvβ3 integrin. In this study we report for the first time the interaction of a Gram-positive extracellular pathogen, namely Streptococcus pneumoniae, with one of the host ICAMs, namely the αvβ3 integrin. In conclusion, the present study analysed some of the aspects of molecular interaction of pneumococcal MSCRAMMs PavA and PavB with hFn and hVn. The hot spots of interaction on C-terminal FnIII repeats were delineated for PavA and PavB. HBD3 was revealed to be pivotal for PavB-Vn interaction. In addition the redundant role of pneumococcal PavB as an MSCRAMM was demonstrated. Furthermore this study successfully identifies a direct receptor for pneumococcal PavB, namely αvβ3 integrin. The mechanism and biological rationale of this newly identified interaction is a matter of debate and awaits further scientific analyses.