Yersinia pestis, the causative agent of plague, expresses the Psa fimbriae (pH 6 antigen) in vitro and in vivo. To evaluate the potential virulence properties of Psa for pneumonic plague, an Escherichia coli strain expressing Psa was engineered and shown to adhere to three types of human respiratory tract epithelial cells. Psa binding specificity was confirmed with Psa-coated polystyrene beads and by inhibition assays. Individual Y. pestis cells were found to be able to express the capsular antigen fraction 1 (F1) concomitantly with Psa on their surface when analyzed by flow cytometry. To better evaluate the separate effects of F1 and Psa on the adhesive and invasive properties of Y. pestis, isogenic ⌬caf (F1 genes), ⌬psa, and ⌬caf ⌬psa mutants were constructed and studied with the three respiratory tract epithelial cells. The ⌬psa mutant bound significantly less to all three epithelial cells compared to the parental wild-type strain and the ⌬caf and ⌬caf ⌬psa mutants, indicating that Psa acts as an adhesin for respiratory tract epithelial cells. An antiadhesive effect of F1 was clearly detectable only in the absence of Psa, underlining the dominance of the Psa ؉ phenotype. Both F1 and Psa inhibited the intracellular uptake of Y. pestis. Thus, F1 inhibits bacterial uptake by inhibiting bacterial adhesion to epithelial cells, whereas Psa seems to block bacterial uptake by interacting with a host receptor that doesn't direct internalization. The ⌬caf ⌬psa double mutant bound and invaded all three epithelial cell types well, revealing the presence of an undefined adhesin(s) and invasin(s).Since the last plague pandemic at the end of the 19th century, its bacterial agent, Yersinia pestis, has been maintained in rodents in several Asian, African, and American countries, including the United States (17, 40). Bubonic plague results from the transmission of Y. pestis by flea bites. In contrast, primary pneumonic plague is acquired when a mammalian host inhales particles or aerosols carrying Y. pestis. Although plague is currently not a major public health problem in developed countries and has been suggested to be less contagious than commonly believed (32), the spread of Y. pestis by aerosols could cause a cluster of human cases of primary pneumonic plague with potential amplification of the outbreak (27).The major adhesins and invasins of enteropathogenic Yersinia pseudotuberculosis and Yersinia enterocolitica (YadA, Ail, and Inv) are not expressed by Y. pestis strains (15,45,51). Thus, how Y. pestis attaches to and translocates through the epithelial layer of the respiratory tract to reach deeper tissues and the bloodstream following airborne transmission remains unknown. Interestingly, Y. pestis exhibits an extensive extracellular lifestyle due to the intracellular delivery of several antiphagocytic effector proteins by its type III secretion system (T3SS-1 or Yops regulon) (5-7, 14, 54, 56). Moreover, two antigenic surface structures exported by usher-chaperone proteins characteristic of fimbrial biogenesis systems...

BackgroundEar infection or otitis media (OM) accounts for most bacterial respiratory infections in children in both developed and developing nations. Streptococcus pneumoniae, nontypeable Haemophilus influenzae, and Moraxella catarrhalis are the major OM pathogens. However, little is known about the genetic basis of bacterial OM largely due to practical difficulties in conducting research in ear infection models and genetically manipulating clinical isolates. Here, we report the first genome-scale in vivo screen for bacterial genes required for ear infection in a chinchilla model by signature tagged mutagenesis (STM), a high throughput mutant screen technique.Methodology/Principal FindingsSTM strains were constructed with a multi-drug resistant OM isolate ST556 (serotype 19F) and screened in a chinchilla OM model. Out of 5,280 mutants tested, 248 mutants were substantially underrepresented in the mutant pools recovered from the middle ear fluids of the infected chinchillas, indicating the impaired ability to survive and replicate in the middle ears due to genetic disruptions in the chromosome of strain ST556. Further DNA sequencing analysis mapped the mutations to 169 pneumococcal genes. Surprisingly, only 52 of these genes were required for pneumococcal nasopharyngeal colonization in a murine model. This infection site-specific gene requirement was verified by targeted mutagenesis in the selected genes.Conclusions/SignificanceThese findings suggest that there are a subset of pneumococcal genes required for ear infection and that these may be distinct from those required for nasal colonization. Our data thus provide comprehensive gene targets for mechanistic understanding of pneumococcal ear infection. Finally, this study has also developed a model for future genome-scale search for virulence determinants in other pathogens associated with ear infections.

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Bone marrow mesenchymal stem cells (BMSC) have the potential to differentiate into a variety of cell types like osteoblasts, chondroblasts, adipocytes, etc. It is well known that mechanical forces regulate the biological function of cells. The aim of this study was to investigate the effect of uniaxial stretching on the orientation and biological functions of BMSC. Rat BMSCs were harvested from femoral and tibial bone marrow by density gradient centrifugation. Cells from passages 1-6 were characterized by flow cytometry using monoclonal antibodies. The recovered cells were stably positive for the markers CD90 and CD44 and negative for CD34 and CD45. A cyclic 10% uniaxial stretching at 1Hz was applied on rat BMSC for different time-courses. The length, width, and orientation of the cells were subsequently determined. Expression of collagen types I and III and tenascin-C mRNAs was measured by real-time RT-PCR, and the synthesis of these receptors was determined by radioimmunoassay. Results showed that uniaxial stretching lengthened and rearranged the cells. Compared with control groups, expression of collagen types I and III mRNAs was up-regulated after 12-h of stretching, while significant increase in synthesis of the two collagen protein types was not observed until after 24-h stretching. The expression of tenascin-C mRNA was significantly increased after a 24-h stretching. These data suggest that cyclic stretching promotes the synthesis of collagen types I and III and tenascin-C by the rat BMSC.

Aim:Previous studies have shown that D(+)β-3,4-dihydroxyphenyl lactic acid (salvianic acid A, SAA) has anabolic effects on prednisone (GC)-induced osteoporosis in rats. The current study aims to investigate the molecular mechanism of SAA's impact on osteogenesis and adipogenesis in bone marrow stromal cells in intact and GC-treated rats. Methods: For in vitro study, newborn rat calvaria osteoblasts (rOBs) and rat bone marrow stromal cells (rMSCs) were isolated, identified and cultured with SAA at different concentrations to evaluate SAA's influence on osteogenesis and adipogenesis. In addition, 3-month-old Sprague-Dawley (SD) male rats were treated with distilled water, prednisone alone (3.0 mg·kg -1 ·d -1 ) or prednisone (3.0 mg·kg -1 ·d -1 ) and SAA (25 mg·kg -1 ·d -1 ) for 45 d. At the end point, the different groups of rMSCs were isolated by density-gradient centrifugation and cultured. Results: (1) At 0.1-10.0 mg/L, SAA increased ALP activity, type I collagen (Coll-I) mRNA and OPG mRNA expression and stimulated nodule mineralization of rOBs. SAA (0.5 mg/L) also significantly increased the ALP activity of rMSCs without a need for osteogenesis-inducing medium. At 5.0 mg/L, SAA decreased the number of adipocytes with less lipid droplet formation from the rMSCs, which typically undergo adipocyte induction. (2) Coll-I expression was markedly decreased, whereas lipoprotein lipase (LPL) mRNA expression increased by 98% when compared with the first generation of rMSCs in GC-treated rats. The SAA-treated rats demonstrated an over 2-fold increase in Coll-I expression when compared with intact rats and further showed a significant decrease in LPL expression when compared with GC-treated rats. When rMSCs were co-cultured with SAA (0.5 mg/L) in vitro, SAA did not affect Coll-I and LPL gene expression in intact rats but significantly increased Coll-I and decreased LPL gene expression in GC-treated rats. Conclusion: SAA protected bone from GC-induced bone marrow impairment by stimulating osteogenesis and depressing adipogenesis in bone marrow stromal cells both in vivo and in vitro. The data indicated that aqueous extract of Salvia miltiorrhiza, which include SAA, may serve as an active anabolic agent and a useful therapeutic strategy for the treatment of GC-associated osteoporosis.