The diverse actions of cytoskeletal vimentin in bacterial infection and host defense.

Bacterial infection is a major threat to human health, with infections resulting in considerable mortality, urging the need for a more profound understanding of bacteria-host interactions. During infection of cells, host cytoskeletal networks constantly interact with bacteria and are integral to their uptake. Vimentin, an intermediate filament protein, is one such cytoskeletal component that interacts with bacteria during infection. Although vimentin is predominantly present in the cytoplasm, it also appears in a secreted form or at the surface of multiple cell types, including epithelial cells, endothelial cells, macrophages and fibroblasts. As a cytoplasmic protein, vimentin participates in bacterial transportation and the consequential immune-inflammatory responses. When expressed on the cell surface, vimentin can be both pro- and anti-bacterial, favoring bacterial invasion in some contexts, but also limiting bacterial survival in others. Vimentin is also secreted and located extracellularly, where it is primarily involved in bacterial-induced inflammation regulation. Reciprocally, bacteria can also manipulate the fate of vimentin in host cells. Given that vimentin is not only involved in bacterial infection, but also the associated life-threatening inflammation, the use of vimentin-targeted drugs might offer a synergistic advantage. In this Review, we recapitulate the abundant evidence on vimentin and its dynamic changes in bacterial infection and speculate on its potential as an anti-bacterial therapeutic target.

Salmonella engages CDC42 effector protein 1 for intracellular invasion.

Human enterocytes are primary targets of infection by invasive bacterium Salmonella Typhimurium, and studies using nonintestinal epithelial cells established that S. Typhimurium activates Rho family GTPases, primarily CDC42, to modulate the actin cytoskeletal network for invasion. The host intracellular protein network that engages CDC42 and influences the pathogen's invasive capacity are relatively unclear. Here, proteomic analyses of canonical and variant CDC42 interactomes identified a poorly characterized CDC42 interacting protein, CDC42EP1, whose intracellular localization is rapidly redistributed and aggregated around the invading bacteria. CDC42EP1 associates with SEPTIN-7 and Villin, and its relocalization and bacterial engagement depend on host CDC42 and S. Typhimurium's capability of activating CDC42. Unlike CDC42, CDC42EP1 is not required for S. Typhimurium's initial cellular entry but is found to associate with Salmonella-containing vacuoles after long-term infections, indicating a contribution to the pathogen's intracellular growth and replication. These results uncover a new host regulator of enteric Salmonella infections, which may be targeted to restrict bacterial load at the primary site of infection to prevent systemic spread.

Deciphering the interaction of bacteria inoculants with the recipient endophytic community in grapevine micropropagated plants.

Engineering the plant microbiome with beneficial endophytic bacteria can improve the growth, health, and productivity of the holobiont. Here, we administered two beneficial bacterial strains, Kosakonia VR04 sp. and Rhizobium GR12 sp., to micropropagated grapevine cuttings obtained via somatic embryogenesis. While both strains colonized the plant endosphere, only Rhizobium GR12 sp. increased root biomass under nutritional-deficit conditions, as supported by the plant growth promotion traits detected in its genome. Phylogenetic and co-occurrence analyses revealed that the plant native bacterial community, originally dominated by Streptococcaceae and Micrococcaceae, dramatically changed depending on the inoculation treatments, as invading strains differently affected the relative abundance and the interactions of pre-existing taxa. After 30 days of plantlets' growth, Pantoea became a predominant taxon, and considering untreated plantlets as references, Rhizobium sp. GR12 showed a minor impact on the endophytic bacterial community. On the other hand, Kosakonia sp. VR04 caused a major change in community composition, suggesting an opportunistic colonization pattern. Overall, the results corroborate the importance of preserving the native endophytic community structure and functions during plant microbiome engineering.IMPORTANCEA better comprehension of bacterial colonization processes and outcomes could benefit the use of plant probiotics in the field. In this study, we applied two different beneficial bacteria to grapevine micropropagated plantlets and described how the inoculation of these strains impacts endophytic microbiota assembly. We showed that under nutritional deficit conditions, the response of the receiving endophytic bacterial communities to the invasion of the beneficial strains related to the manifestation of plant growth promotion effects by the inoculated invading strains. Rhizobium sp. GR12 was able to preserve the native microbiome structure despite its effective colonization, highlighting the importance of the plant-endophyte associations for the holobiont performance. Moreover, our approach showed that the use of micropropagated plantlets could be a valuable strategy to study the interplay among the plant, its native microbiota, and the invader on a wider portfolio of species besides model plants, facilitating the application of new knowledge in agriculture.

The Balance between Protealysin and Its Substrate, the Outer Membrane Protein OmpX, Regulates Serratia proteamaculans Invasion.

Serratia are opportunistic bacteria, causing infections in plants, insects, animals and humans under certain conditions. The development of bacterial infection in the human body involves several stages of host-pathogen interaction, including entry into non-phagocytic cells to evade host immune cells. The facultative pathogen Serratia proteamaculans is capable of penetrating eukaryotic cells. These bacteria synthesize an actin-specific metalloprotease named protealysin. After transformation with a plasmid carrying the protealysin gene, noninvasive E. coli penetrate eukaryotic cells. This suggests that protealysin may play a key role in S. proteamaculans invasion. This review addresses the mechanisms underlying protealysin's involvement in bacterial invasion, highlighting the main findings as follows. Protealysin can be delivered into the eukaryotic cell by the type VI secretion system and/or by bacterial outer membrane vesicles. By cleaving actin in the host cell, protealysin can mediate the reversible actin rearrangements required for bacterial invasion. However, inactivation of the protealysin gene leads to an increase, rather than decrease, in the intensity of S. proteamaculans invasion. This indicates the presence of virulence factors among bacterial protealysin substrates. Indeed, protealysin cleaves the virulence factors, including the bacterial surface protein OmpX. OmpX increases the expression of the EGFR and ß1 integrin, which are involved in S. proteamaculans invasion. It has been shown that an increase in the invasion of genetically modified S. proteamaculans may be the result of the accumulation of full-length OmpX on the bacterial surface, which is not cleaved by protealysin. Thus, the intensity of the S. proteamaculans invasion is determined by the balance between the active protealysin and its substrate OmpX.

Involvement of Lipid Rafts in the Invasion of Opportunistic Bacteria Serratia into Eukaryotic Cells.

Cell membrane rafts form signaling platforms on the cell surface, controlling numerous protein-protein and lipid-protein interactions. Bacteria invading eukaryotic cells trigger cell signaling to induce their own uptake by non-phagocytic cells. The aim of this work was to reveal the involvement of membrane rafts in the penetration of the bacteria Serratia grimesii and Serratia proteamaculans into eukaryotic cells. Our results show that the disruption of membrane rafts by MßCD in the three cell lines tested, M-HeLa, MCF-7 and Caco-2, resulted in a time-dependent decrease in the intensity of Serratia invasion. MßCD treatment produced a more rapid effect on the bacterial susceptibility of M-HeLa cells compared to other cell lines. This effect correlated with a faster assembly of the actin cytoskeleton upon treatment with MßCD in M-HeLa cells in contrast to that in Caco-2 cells. Moreover, the 30 min treatment of Caco-2 cells with MßCD produced an increase in the intensity of S. proteamaculans invasion. This effect correlated with an increase in EGFR expression. Together with the evidence that EGFR is involved in S. proteamaculans invasion but not in S. grimesii invasion, these results led to the conclusion that an increase in EGFR amount on the plasma membrane with the undisassembled rafts of Caco-2 cells after 30 min of treatment with MßCD may increase the intensity of S. proteamaculans but not of S. grimesii invasion. Thus, the MßCD-dependent degradation of lipid rafts, which enhances actin polymerization and disrupts signaling pathways from receptors on the host cell's surface, reduces Serratia invasion.

Host-Cell-Dependent Roles of E-Cadherin in Serratia Invasion.

Bacteria use cell surface proteins to mediate host-pathogen interactions. Proteins responsible for cell adhesion, including E-cadherin, serve as receptors for entry into the host cell. We have previously shown that an increase in eukaryotic cell sensitivity to Serratia grimesii correlates with an increase in E-cadherin expression. On the other hand, Serratia proteamaculans invasion involves the EGFR, which can interact with E-cadherin on the surface of host cells. Therefore, we investigated the role of E-cadherin in Serratia invasion into M-HeLa and Caco-2 cells. Bacterial infection increased E-cadherin expression in both cell lines. Moreover, E-cadherin was detected in the Caco-2 cells in a full-length form and in the M-HeLa cells in only a truncated form in response to incubation with bacteria. Transfection with siRNA targeting E-cadherin inhibited S. proteamaculans invasion only into the Caco-2 cells. Thus, only full-length E-cadherin is involved in S. proteamaculans invasion. On the other hand, transfection with siRNA targeting E-cadherin inhibited S. grimesii invasion into both cell lines. Thus, not only may full-length E-cadherin but also truncated E-cadherin be involved in S. grimesii invasion. Truncated E-cadherin can be formed as a result of cleavage by bacterial proteases or the Ca2+-activated cellular protease ADAM10. The rate of Ca2+ accumulation in the host cells depends on the number of bacteria per cell upon infection. During incubation, Ca2+ accumulates only when more than 500 S. grimesii bacteria are infected per eukaryotic cell, and only under these conditions does the ADAM10 inhibitor reduce the sensitivity of the cells to bacteria. An EGFR inhibitor has the same quantitative effect on S. grimesii invasion. Apparently, as a result of infection with S. grimesii, Ca2+ accumulates in the host cells and may activate the ADAM10 sheddase, which can promote invasion by cleaving E-cadherin and, as a result, triggering EGFR signaling. Thus, the invasion of S. proteamaculans can only be promoted by full-length E-cadherin, and S. grimesii invasion can be promoted by both full-length and truncated E-cadherin.

Intensive management facilitates bacterial invasion on soil microbial community.

Intensive management has greatly altered natural forests, especially forests around the world are increasingly being converted into economic plantations. Soil microbiota are critical for community functions in all ecosystems, but the effects of microbial disturbance during economic plantation remain unclear. Here, we used Escherichia coli O157:H7, a model pathogenic species for bacterial invasion, to assess the invasion impacts on the soil microbial community under intensive management. The E. coli invasion was tracked for 135 days to explore the instant and legacy impacts on the resident community. Our results showed that bamboo economic plantations altered soil abiotic and biotic properties, especially increasing pH and community diversity. Higher pH in bamboo soils resulted in longer pathogen survivals than in natural hardwood soils, indicating that pathogen suppression during intensive management should arouse our attention. A longer invasion legacy effect on the resident community (P < 0.05) were found in bamboo soils underlines the need to quantify the soil resilience even when the invasion was unsuccessful. Deterministic processes drove community assembly in bamboo plantations, and this selection acted more strongly during by E. coli invasion than in hardwood soils. We also showed more associated co-occurrence patterns in bamboo plantations, suggesting more complex potential interactions within the microbial community. Apart from community structure, community functions are also strongly related to the resident species associated with invaders. These findings provide new perspectives to understand intensive management facilitates the bacterial invasion, and the impacts would leave potential risks on environmental and human health.

Molecular identification and functional exploration of interleukin-20 in snakehead (Channa argus) involved in bacterial invasion and the proliferation of head kidney leukocytes.

As an inflammatory cytokine of the interleukin-20 (IL-20) subfamily, IL-20 has various functions in immune defenses, inflammatory diseases, tissue regeneration, cancer, and metabolism. Although the characteristics and functions of mammalian IL-20 have been clarified, those of fish IL-20 remain unclear. In this study, the IL-20 gene from the snakehead Channa argus (shIL-20) was cloned and functionally characterized. Similar to the IL-20 homologues of other species, the shIL-20 has a five exon/four intron structure in the coding region. The open reading frame of shIL-20 consists of 528 base pairs and encodes 175 amino acids (aa), including a signal peptide (aa 1-24) and a mature peptide (aa 25-175). The mature shIL-20 protein has six conserved cysteine residues, which occur in the IL-20 proteins of all species analyzed, and an additional cysteine residue (Cys-82) found only in the IL-20 proteins of several teleosts. The modeled tertiary structure of shIL-20 is similar with that of Homo sapiens IL-20. The shIL-20 was expressed constitutively in all the tissues analyzed, and its transcription was induced in the spleen and head kidney by Aeromonas schubertii and Nocardia seriolae in vivo and in head kidney leukocytes (HKLs) by lipoteichoic acid, lipopolysaccharide, and polyinosinic-polycytidylic acid in vitro. The recombinant shIL-20 protein induced the transcription of tumor necrosis factor α1 (TNF-α1), TNF-α2, IL-1ß, and endogenous shIL-20, and promoted the proliferation of HKLs. In conclusion, these findings demonstrate that shIL-20 participates in the immune response to bacterial invasion and promotes leukocyte proliferation, offering new insights into the functions of fish IL-20 during pathogen invasion.

Bacterial quorum sensing facilitates Xanthomonas campesteris pv. campestris invasion of host tissue to maximize disease symptoms.

Quorum sensing (QS) helps the Xanthomonas group of phytopathogens to infect several crop plants. The vascular phytopathogen Xanthomonas campestris pv. campestris (Xcc) is the causal agent of black rot disease on Brassicaceae leaves, where a typical v-shaped lesion spans both vascular and mesophyll regions with progressive leaf chlorosis. Recently, the role of QS has been elucidated during Xcc early infection stages. However, a detailed insight into the possible role of QS-regulated bacterial invasion in host chlorophagy during late infection stages remains elusive. In this study, using QS-responsive whole-cell bioreporters of Xcc, we present a detailed chronology of QS-facilitated Xcc colonization in the mesophyll region of cabbage (Brassica oleracea) leaves. We report that QS-enabled localization of Xcc to parenchymal chloroplasts triggers leaf chlorosis and promotion of systemic infection. Our results indicate that the QS response in the Xanthomonas group of vascular phytopathogens maximizes their population fitness across host tissues to trigger stage-specific host chlorophagy and establish a systemic infection.

Strategies used by bacterial pathogens to cross the blood-brain barrier.

The skull, spine, meninges, and cellular barriers at the blood-brain and the blood-cerebrospinal fluid interfaces well protect the brain and meningeal spaces against microbial invasion. However, once in the bloodstream, a range of pathogenic bacteria is able to reach the brain and cause meningitis. Despite advances in antibacterial therapy, bacterial meningitis remains one of the most important infectious diseases worldwide. The most common causative bacteria in children and adults are Streptococcus pneumoniae and Neisseria meningitidis associated with high morbidity and mortality, while among neonates, most cases of bacterial meningitis are due to group B Streptococcus and Escherichia coli. Here we summarise our current knowledge on the strategies used by these bacterial pathogens to survive in the bloodstream, to colonise the brain vasculature and to cross the blood-brain barrier.

Effect of scaling on the invasion of oral microorganisms into dentinal tubules including the response of pulpal cells-an in vitro study.

OBJECTIVES: To investigate how scaling affects the penetration of microorganisms into dentinal tubules, how pulpal cells seeded into the pulp cavity respond to bacterial challenge, and how penetration and inflammatory response may depend on the bacterial composition. MATERIALS AND METHODS: Root canals of 102 extracted human teeth underwent shaping and cleaning. Half of the teeth were subjected to scaling and root planing, the other half remained untreated. Teeth were exposed to either Streptococcus gordonii and Actinomyces oris or S. gordonii and Porphyromonas gingivalis for 10 weeks. Bacterial invasion was assessed in a depth of 1 mm to the root surface. Human pulpal cells were seeded into the cavities to assess the expression of interleukin-8 (IL-8), monocyte chemoattractant protein-1 (MCP-1), and matrix metalloproteinase-3 (MMP-3) by real-time polymerase chain reaction and immunoassay. RESULTS: The percentage of teeth with bacteria detected in dentine was higher when teeth received scaling than when they were untreated: 66.6% versus 44.4% when exposed to A. oris/S. gordonii, and 50% versus 25% when exposed to P. gingivalis/S. gordonii (p = 0.043). Scaling had no impact on IL-8 and MMP-3 expression in pulpal cells. P. gingivalis/S. gordonii caused higher levels of IL-8, MCP-1, and MMP-3 than A. oris/S. gordonii (p = 0.003, p = 0.011, p = 0.037). CONCLUSION: Scaling supports the penetration of bacteria into the dentine of extracted human teeth. P. gingivalis may affect the immune response in pulpal cells. CLINICAL RELEVANCE: Root surface debridement with hand instruments may facilitate bacterial penetration. Other kinds of mechanical instrumentation in this experimental setting should be investigated.

Bacterial Outer Membrane Protein OmpX Regulates ß1 Integrin and Epidermal Growth Factor Receptor (EGFR) Involved in Invasion of M-HeLa Cells by Serratia proteamaculans.

Opportunistic pathogen Serratia proteamaculans are able to penetrate the eukaryotic cells. The penetration rate can be regulated by bacterial surface protein OmpX. OmpX family proteins are able to bind to host cell surface to the epidermal growth factor receptor (EGFR) and the extracellular matrix protein fibronectin, whose receptors are in return the α5 ß1 integrins. Here we elucidated the involvement of these host cell proteins in S. proteamaculans invasion. We have shown that, despite the absence of fibronectin contribution to S. proteamaculans invasion, ß1 integrin was directly involved in invasion of M-HeLa cells. Herewith ß1 integrin was not the only receptor that determines sensitivity of host cells to bacterial invasion. Signal transfer from EGFR was also involved in the penetration of these bacteria into M-HeLa cells. However, M-HeLa cells have not been characterized by large number of these receptors. It turned out that S. proteamaculans attachment to the host cell surface resulted in an increment of EGFR and ß1 integrin genes expression. Such gene expression increment also caused Escherichia coli attachment, transformed with a plasmid encoding OmpX from S. proteamaculans. Thus, an OmpX binding to the host cell surface caused an increase in the EGFR and ß1 integrin expression involved in S. proteamaculans invasion.

The Serratia grimesii outer membrane vesicles-associated grimelysin triggers bacterial invasion of eukaryotic cells.

Serratia grimesii are facultative pathogenic bacteria that can penetrate a wide range of host cells and cause infection, especially in immunocompromised patients. Previously, we have found that bacterial metalloprotease grimelysin is a potential virulence determinant of S. grimesii invasion (E. S. Bozhokina et al., (2011). Cell Biology International, 35(2), 111-118). Protease is characterized as an actin-hydrolyzing enzyme with a narrow specificity toward other cell proteins. It is not known, however, whether grimelysin is transported into eukaryotic cells. Here, we show, for the first time, that S. grimesii can generate outer membrane vesicles (OMVs) displayed specific proteolytic activity against actin, characteristic of grimelysin. The presence of grimelysin was also confirmed by the Western blot analysis of S. grimesii OMVs lysate. Furthermore, confocal microscopy analysis revealed that the S. grimesii grimelysin-containing OMVs attached to the host cell membrane. Finally, pretreatment of HeLa cells with S. grimesii OMVs before the cells were infected with bacteria increased the bacterial penetration several times. These data strongly suggest that protease grimelysin promotes S. grimesii internalization by modifying bacterial and/or host molecule(s) when it is delivered as a component of OMVs.

Bacterial Actin-Specific Endoproteases Grimelysin and Protealysin as Virulence Factors Contributing to the Invasive Activities of Serratia.

The article reviews the discovery, properties and functional activities of new bacterial enzymes, proteases grimelysin (ECP 32) of Serratia grimesii and protealysin of Serratia proteamaculans, characterized by both a highly specific "actinase" activity and their ability to stimulate bacterial invasion. Grimelysin cleaves the only polypeptide bond Gly42-Val43 in actin. This bond is not cleaved by any other proteases and leads to a reversible loss of actin polymerization. Similar properties were characteristic for another bacterial protease, protealysin. These properties made grimelysin and protealysin a unique tool to study the functional properties of actin. Furthermore, bacteria Serratia grimesii and Serratia proteamaculans, producing grimelysin and protealysin, invade eukaryotic cells, and the recombinant Escherichia coli expressing the grimelysin or protealysins gene become invasive. Participation of the cellular c-Src and RhoA/ROCK signaling pathways in the invasion of eukaryotic cells by S. grimesii was shown, and involvement of E-cadherin in the invasion has been suggested. Moreover, membrane vesicles produced by S. grimesii were found to contain grimelysin, penetrate into eukaryotic cells and increase the invasion of bacteria into eukaryotic cells. These data indicate that the protease is a virulence factor, and actin can be a target for the protease upon its translocation into the host cell.

An appraisal of the role of specific bacteria in the initial pathogenesis of periodontitis.

BACKGROUND: Historically, inflammatory periodontal diseases (gingivitis and periodontitis) have been recognized as being primarily of bacterial origin. Bacteria are necessary for disease development, but the presence of specific bacteria does not guarantee progression to periodontitis. Periodontitis is a multifactorial disease; specific bacteria are associated with disease, but may not be the target of treatment. Gingivitis and periodontitis are inflammatory conditions associated with bacterial overgrowth. AIM: To analyse evidence for established thought that specific bacteria directly participate in the pathogenesis of periodontitis and question the long-held tenet that penetration of the periodontal connective tissues by bacteria and their products is a significant phase in the initial development of periodontitis. METHODS: The literature was searched for studies on initiation of gingivitis and periodontitis by specific pathogens. The search results were insufficient for a systematic review and have been summarized in a commentary instead. RESULTS: There is very little evidence in the literature to support the commonly held concept that specific bacteria initiate periodontitis. CONCLUSION: We present evidence for a paradigm supporting the central role of inflammation, rather than specific microbiota, in the early pathogenesis of periodontitis, and discuss whether controlling the inflammation can influence the character and composition of the periodontal infection.

Anaplasma marginale Outer Membrane Protein A Is an Adhesin That Recognizes Sialylated and Fucosylated Glycans and Functionally Depends on an Essential Binding Domain.

Anaplasma marginale causes bovine anaplasmosis, a debilitating and potentially fatal tick-borne infection of cattle. Because A. marginale is an obligate intracellular organism, its adhesins that mediate entry into host cells are essential for survival. Here, we demonstrate that A. marginale outer membrane protein A (AmOmpA; AM854) contributes to the invasion of mammalian and tick host cells. AmOmpA exhibits predicted structural homology to OmpA of A. phagocytophilum (ApOmpA), an adhesin that uses key lysine and glycine residues to interact with α2,3-sialylated and α1,3-fucosylated glycan receptors, including 6-sulfo-sialyl Lewis x (6-sulfo-sLex). Antisera against AmOmpA or its predicted binding domain inhibits A. marginale infection of host cells. Residues G55 and K58 are contributory, and K59 is essential for recombinant AmOmpA to bind to host cells. Enzymatic removal of α2,3-sialic acid and α1,3-fucose residues from host cell surfaces makes them less supportive of AmOmpA binding. AmOmpA is both an adhesin and an invasin, as coating inert beads with it confers adhesiveness and invasiveness. Recombinant forms of AmOmpA and ApOmpA competitively antagonize A. marginale infection of host cells, but a monoclonal antibody against 6-sulfo-sLex fails to inhibit AmOmpA adhesion and A. marginale infection. Thus, the two OmpA proteins bind related but structurally distinct receptors. This study provides a detailed understanding of AmOmpA function, identifies its essential residues that can be targeted by blocking antibody to reduce infection, and determines that it binds to one or more α2,3-sialylated and α1,3-fucosylated glycan receptors that are unique from those targeted by ApOmpA.

Bacterial invasion into radicular dentine-an in vitro study.

OBJECTIVES: We wanted to investigate differences in invasiveness into radicular dentinal tubules by monocultured and co-cultured bacteria frequently found in infected root canals. METHODS: Fifty-one human roots were incubated for 8 weeks with monocultured Streptococcus gordonii ATCC 10558, Streptococcus sanguinis ATCC 10556, and with five capnophiles/anaerobes as well as with capnophiles/anaerobes co-cultured with a streptococcal species. Thereafter, bacterial samples were cultured from the inner, middle, and outer third of the root dentine of longitudinally broken teeth (n = 5). In addition, scanning electron microscopy (SEM) images were obtained. RESULTS: Single gram-positive species were able to penetrate into the middle and outer third of the root dentine. Fusobacterium nucleatum ATCC 25586 was not found in any of the dentine specimens. Prevotella intermedia ATCC 25611 and Porphyromonas gingivalis ATCC 33277 were found in the inner and middle third. The bacterial load of streptococci was higher in all thirds in co-cultures compared to single infections. In co-cultures with streptococci, Actinomyces oris ATCC 43146 was found in the outer third in 9/10 samples, whereas P. intermedia ATCC 25611 was not detectable inside dentine. Co-culture with S. sanguinis ATCC 10556 enabled F. nucleatum ATCC 25586 to invade dentine; SEM images showed that F. nucleatum ATCC 25586 had a swollen shape. CONCLUSIONS: Invasiveness of bacteria into dentinal tubules is species-specific and may change depending on culturing as a single species or co-culturing with other bacteria. CLINICAL RELEVANCE: Oral streptococci may promote or inhibit invasion of capnophiles/anaerobes into radicular dentine.

A Prophage in Diabetic Foot Ulcer-Colonizing Staphylococcus aureus Impairs Invasiveness by Limiting Intracellular Growth.

The mechanisms that drive the transition from commensality to invasiveness in Staphylococcus aureus are poorly understood. We recently reported that >50% of S. aureus isolates from uninfected diabetic foot ulcers in French patients harbor a prophage, ROSA-like, that is absent from invasive isolates from diabetic foot infections, including osteomyelitis. Here we show that the ROSA-like insertion abolishes the ability of S. aureus to replicate within osteoblasts, the bone-forming cells, greatly reducing damage to infected cells. These results unravel an important mechanism by which particular S. aureus strains are maintained in a commensal state in diabetic foot ulcers.

Staphylococcus aureus keratinocyte invasion is mediated by integrin-linked kinase and Rac1.

Staphylococcus aureus is a major component of the skin microbiota and causes a large number of serious infections. S. aureus first interacts with epidermal keratinocytes to breach the epidermal barrier through mechanisms not fully understood. By use of primary keratinocytes from mice with epidermis-restricted Ilk gene inactivation and control integrin-linked kinase (ILK)-expressing littermates, we investigated the role of ILK in epidermal S. aureus invasion. Heat-killed, but not live, bacteria were internalized to Rab5- and Rab7-positive phagosomes, and incubation with keratinocyte growth factor increased their uptake 2.5-fold. ILK-deficient mouse keratinocytes internalized bacteria 2- to 4-fold less efficiently than normal cells. The reduced invasion by live S. aureus of ILK-deficient cells was restored in the presence of exogenous, constitutively active Rac1. Thus, Rac1 functions downstream from ILK during invasion. Further, invasion by S. aureus of Rac1-deficient cells was 2.5-fold lower than in normal cells. Paradoxically, staphylococcal cutaneous penetration of mouse skin explants with ILK-deficient epidermis was 35-fold higher than that of normal skin, indicating defects in epidermal barrier function in the absence of ILK. Thus, we identified an ILK-Rac1 pathway essential for bacterial invasion of keratinocytes, and established ILK as a key contributor to prevent invasive staphylococcal cutaneous infection.

Caged xanthones: Potent inhibitors of global predominant MRSA USA300.

Total of 22 caged xanthones were subjected to susceptibility testing of global epidemic MRSA USA300. Natural morellic acid showed the strongest potency (MIC of 12.5µM). However, its potent toxicity diminishes MRSA therapeutic potential. We synthetically modified natural morellic acid to yield 13 derivatives (3a-3m). Synthetically modified 3b retained strong potency in MRSA growth inhibition, yet the toxicity was 20-fold less than natural morellic acid, permitting the possibility of using caged xanthones for MRSA therapeutic.