Estrogen deficiency is a major risk factor for osteoporosis that is associated with bone inflammation and resorption. Half of women over the age of 50 will experience an osteoporosis related fracture in their lifetime, thus novel therapies are needed to combat post-menopausal bone loss. Recent studies suggest an important role for gut-bone signaling pathways and the microbiota in regulating bone health. Given that the bacterium Lactobacillus reuteri ATCC PTA 6475 (L. reuteri) secretes beneficial immunomodulatory factors, we examined if this candidate probiotic could reduce bone loss associated with estrogen deficiency in an ovariectomized (Ovx) mouse menopausal model. Strikingly, L. reuteri treatment significantly protected Ovx mice from bone loss. Osteoclast bone resorption markers and activators (Trap5 and RANKL) as well as osteoclastogenesis are significantly decreased in L. reuteri treated mice. Consistent with this, L. reuteri suppressed Ovx-induced increases in bone marrow CD4+ T-lymphocytes (which promote osteoclastogenesis) and directly suppressed osteoclastogenesis in vitro. We also identif ied that L. reuteri treatment modifies microbial communities in the Ovx mouse gut. Together, our studies demonstrate that L. reuteri treatment suppresses bone resorption and loss associated with estrogen deficiency. Thus, L. reuteri treatment may be a straightforward and cost-effective approach to reduce post-menopausal bone loss.

In humans, Streptococcus pneumoniae (SPN) is the leading cause of bacterial meningitis, a disease with high attributable mortality and frequent permanent neurological sequelae. The molecular mechanisms underlying the central nervous system tropism of SPN are incompletely understood, but include a primary interaction of the pathogen with the blood–brain barrier (BBB) endothelium. All SPN strains possess a gene encoding the surface-anchored sialidase (neuraminidase) NanA, which cleaves sialic acid on host cells and proteins. Here, we use an isogenic SPN NanA-deficient mutant and heterologous expression of the protein to show that NanA is both necessary and sufficient to promote SPN adherence to and invasion of human brain microvascular endothelial cells (hBMECs). NanA-mediated hBMEC invasion depends only partially on sialidase activity, whereas the N-terminal lectinlike domain of the protein plays a critical role. NanA promotes SPN–BBB interaction in a murine infection model, identifying the protein as proximal mediator of CNS entry by the pathogen.

Background Group B Streptococcus (GBS) is the leading cause of bacterial meningitis in newborn infants. As GBS is able to invade, survive and cross the blood-brain barrier (BBB), we sought to identify surface-expressed virulence factors that contribute to BBB penetration and the pathogenesis of meningitis. Methods Targeted deletion and insertional mutants were generated in different GBS clinical isolates. Wild type and mutant bacteria were analyzed for their capacity to adhere and invade human brain microvascular endothelial cells (hBMEC) and penetrate the BBB using our model of hematogeneous meningitis. Results Analysis of a GBS (serotype V) clinical isolate revealed the presence of a surface anchored serine-rich protein previously designated serine-rich repeat-1 (Srr-1). GBS Srr-1 is a high molecular weight glycosylated protein. Deletion of srr1 in NCTC 10/84 resulted in a significant decrease in adherence and invasion of hBMEC. Additional mutants in other GBS serotypes commonly associated with meningitis showed a similar decrease in hBMEC invasion compared to parental strains. Finally, wild type GBS penetrated the BBB and established meningitis more frequently than mice challenged with the Δsrr1 mutant strain. Conclusion Our data suggest that GBS Srr glycoproteins play an important role in crossing the BBB and the development of streptococcal meningitis.

Group B Streptococcus (GBS) is a major cause of invasive bacterial infections in newborns and certain adult populations. Surface filamentous appendages known as pili have been recently identified in GBS. However, little is known about the role of these structures in disease pathogenesis. In this study we sought to probe potential functional role(s) of PilB, the major GBS pilus protein subunit, by coupling analysis of an isogenic GBS pilB knockout strain with heterologous expression of the pilB gene in the nonpathogenic bacterium Lactococcus lactis. We found the knockout GBS strain that lacked PilB was more susceptible than wild-type (WT) GBS to killing by isolated macrophages and neutrophils. Survival was linked to the ability of PilB to mediate GBS resistance to cathelicidin antimi-crobial peptides. Furthermore, the PilB-deficient GBS mutant was more readily cleared from the mouse bloodstream and less-virulent in vivo compared to the WT parent strain. Strikingly, overexpression of the pilB gene alone in L. lactis enhanced resistance to phagocyte killing, increased bloodstream survival, and conferred virulence in a mouse challenge model. Together these data demonstrate that the pilus backbone subunit, PilB, plays an integral role in GBS virulence and suggests a novel role for gram-positive pili in thwarting the innate defenses of phagocyte killing. Keywords Streptococcus agalactiae; pili; GBS; macrophage; neutrophil; antimicrobial peptidesThe gram-positive bacterium Group B Streptococcus (GBS) is a major cause of pneumonia, sepsis, and meningitis in newborns and is increasingly associated with disease in adult populations including the elderly, pregnant women, and diabetics (1). Cell surface-expressed NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript filamentous appendages known as pili have recently been identified in streptococcal pathogens that cause invasive infections in humans, including GBS (2), Group A Streptococcus (GAS) (3), and Streptococcus pneumoniae (4). Pili, also known as fimbriae, are non-flagellar polymeric organelles often involved in bacterial adherence to host cells and tissues during colonization. The analysis of multiple GBS genomes has revealed the presence of specific genetic islands that contain the necessary components for pilus formation (5). In all cases that have been described so far, the genes that encode the pilus proteins are clustered at the same genetic locus, transcribed in the same direction, and are likely part of an operon (6). The pilus operon codes for three proteins with the conserved C-terminal amino acid motif LP(X)TG for subsequent cell wall anchoring, and two genes encoding sortases required for complete pilus assembly. Recent studies have demonstrated that a single GBS pilin protein constitutes the major pilus subunit or bona fide pilus, while ancillary proteins are incorporated at the tip or base of the pilus structure (5,7,8). In addition, an immediate upstream transcriptional regulator has been shown to activate the expression of...