Human milk oligosaccharides inhibit growth of group B Streptococcus.

Streptococcus agalactiae (group B Streptococcus, GBS) is a leading cause of invasive bacterial infections in newborns, typically acquired vertically during childbirth secondary to maternal vaginal colonization. Human milk oligosaccharides (HMOs) have important nutritional and biological activities that guide the development of the immune system of the infant and shape the composition of normal gut microbiota. In this manner, HMOs help protect against pathogen colonization and reduce the risk of infection. In the course of our studies of HMO-microbial interactions, we unexpectedly uncovered a novel HMO property to directly inhibit the growth of GBS independent of host immunity. By separating different HMO fractions through multidimensional chromatography, we found the bacteriostatic activity to be confined to specific non-sialylated HMOs and synergistic with a number of conventional antibiotic agents. Phenotypic screening of a GBS transposon insertion library identified a mutation within a GBS-specific gene encoding a putative glycosyltransferase that confers resistance to HMOs, suggesting that HMOs may function as an alternative substrate to modify a GBS component in a manner that impairs growth kinetics. Our study uncovers a unique antibacterial role for HMOs against a leading neonatal pathogen and expands the potential therapeutic utility of these versatile molecules.

Natural Product Anacardic Acid from Cashew Nut Shells Stimulates Neutrophil Extracellular Trap Production and Bactericidal Activity.

Emerging antibiotic resistance among pathogenic bacteria is an issue of great clinical importance, and new approaches to therapy are urgently needed. Anacardic acid, the primary active component of cashew nut shell extract, is a natural product used in the treatment of a variety of medical conditions, including infectious abscesses. Here, we investigate the effects of this natural product on the function of human neutrophils. We find that anacardic acid stimulates the production of reactive oxygen species and neutrophil extracellular traps, two mechanisms utilized by neutrophils to kill invading bacteria. Molecular modeling and pharmacological inhibitor studies suggest anacardic acid stimulation of neutrophils occurs in a PI3K-dependent manner through activation of surface-expressed G protein-coupled sphingosine-1-phosphate receptors. Neutrophil extracellular traps produced in response to anacardic acid are bactericidal and complement select direct antimicrobial activities of the compound.

Role of Hypoxia Inducible Factor-1α (HIF-1α) in Innate Defense against Uropathogenic Escherichia coli Infection.

Uropathogenic E. coli (UPEC) is the primary cause of urinary tract infections (UTI) affecting approximately 150 million people worldwide. Here, we revealed the importance of transcriptional regulator hypoxia-inducible factor-1 α subunit (HIF-1α) in innate defense against UPEC-mediated UTI. The effects of AKB-4924, a HIF-1α stabilizing agent, were studied using human uroepithelial cells (5637) and a murine UTI model. UPEC adherence and invasion were significantly reduced in 5637 cells when HIF-1α protein was allowed to accumulate. Uroepithelial cells treated with AKB-4924 also experienced reduced cell death and exfoliation upon UPEC challenge. In vivo, fewer UPEC were recovered from the urine, bladders and kidneys of mice treated transurethrally with AKB-4924, whereas increased bacteria were recovered from bladders of mice with a HIF-1α deletion. Bladders and kidneys of AKB-4924 treated mice developed less inflammation as evidenced by decreased pro-inflammatory cytokine release and neutrophil activity. AKB-4924 impairs infection in uroepithelial cells and bladders, and could be correlated with enhanced production of nitric oxide and antimicrobial peptides cathelicidin and ß-defensin-2. We conclude that HIF-1α transcriptional regulation plays a key role in defense of the urinary tract against UPEC infection, and that pharmacological HIF-1α boosting could be explored further as an adjunctive therapy strategy for serious or recurrent UTI.

Human milk oligosaccharides protect bladder epithelial cells against uropathogenic Escherichia coli invasion and cytotoxicity.

The invasive pathogen uropathogenic Escherichia coli (UPEC) is the primary cause of urinary tract infections (UTIs). Recurrent infection that can progress to life-threatening renal failure has remained as a serious global health concern in infants. UPEC adheres to and invades bladder epithelial cells to establish infection. Studies have detected the presence of human milk oligosaccharides (HMOs) in urine of breast-fed, but not formula-fed, neonates. We investigated the mechanisms HMOs deploy to elicit protection in human bladder epithelial cells infected with UPEC CFT073, a prototypic urosepsis-associated strain. We found a significant reduction in UPEC internalization into HMO-pretreated epithelial cells without observing any significant effect in UPEC binding to these cells. This event coincides with a rapid decrease in host cell cytotoxicity, recognized by LIVE/DEAD staining and cell detachment, but independent of caspase-mediated or mitochondrial-mediated programmed cell death pathways. Further investigation revealed HMOs, and particularly the sialic acid-containing fraction, reduced UPEC-mediated MAPK and NF-κB activation. Collectively, our results indicate that HMOs can protect bladder epithelial cells from deleterious cytotoxic and proinflammatory effects of UPEC infection, and may be one contributing mechanism underlying the epidemiological evidence of reduced UTI incidence in breast-fed infants.

Shigella flexneri utilize the spectrin cytoskeleton during invasion and comet tail generation.

BACKGROUND: The spectrin cytoskeleton is emerging as an important host cell target of enteric bacterial pathogens. Recent studies have identified a crucial role for spectrin and its associated proteins during key pathogenic processes of Listeria monocytogenes and Salmonella Typhimurium infections. Here we investigate the involvement of spectrin cytoskeletal components during the pathogenesis of the invasive pathogen Shigella flexneri. RESULTS: Immunofluorescent microscopy reveals that protein 4.1 (p4.1), but not adducin or spectrin, is robustly recruited to sites of S. flexneri membrane ruffling during epithelial cell invasion. Through siRNA-mediated knockdowns, we identify an important role for spectrin and the associated proteins adducin and p4.1 during S. flexneri invasion. Following internalization, all three proteins are recruited to the internalized bacteria, however upon generation of actin-rich comet tails, we observed spectrin recruitment to those structures in the absence of adducin or p4.1. CONCLUSION: These findings highlight the importance of the spectrin cytoskeletal network during S. flexneri pathogenesis and further demonstrate that pathogenic events that were once thought to exclusively recruit the actin cytoskeletal system require additional cytoskeletal networks.

Eps15 and Epsin1 are crucial for enteropathogenic Escherichia coli pedestal formation despite the absence of adaptor protein 2.

Enteropathogenic Escherichia coli (EPEC) are primarily extracellular pathogens that generate actin-rich structures known as pedestals during their pathogenesis. Surprising evidence has demonstrated that despite maintaining an extracellular location, EPEC require the endocytic protein, clathrin, for pedestal formation. To evaluate the strategies EPEC use to usurp endocytic machinery, we investigated the roles of a number of clathrin-coated pits components, adaptor protein 2 (AP-2), Eps15 and epsin1, during EPEC infections. We demonstrated that in conjunction with clathrin, pedestal formation also required the recruitment of Eps15 and epsin1 but not AP-2. Because AP-2 orchestrates the recruitment of clathrin, Eps15, and epsin1, as well as other adaptors, during assembly of clathrin-coated pits at the plasma membrane, our findings reveal a novel internalization subversion strategy employed by EPEC. These results further emphasize the recent paradigm that endocytic proteins are important for EPEC-mediated disease.

Role for CD2AP and other endocytosis-associated proteins in enteropathogenic Escherichia coli pedestal formation.

Enteropathogenic Escherichia coli (EPEC) strains are extracellular pathogens that generate actin-rich structures (pedestals) beneath the adherent bacteria as part of their virulence strategy. Pedestals are hallmarks of EPEC infections, and their efficient formation in vitro routinely requires phosphorylation of the EPEC effector protein Tir at tyrosine 474 (Y474). This phosphorylation results in the recruitment and direct attachment of the host adaptor protein Nck to Tir at Y474, which is utilized for actin nucleation through a downstream N-WASP-Arp2/3-based mechanism. Recently, the endocytic protein clathrin was demonstrated to be involved in EPEC pedestal formation. Here we examine the organization of clathrin in pedestals and report that CD2AP, an endocytosis-associated and cortactin-binding protein, is a novel and important component of EPEC pedestal formation that also utilizes Y474 phosphorylation of EPEC Tir. We also demonstrate the successive recruitment of Nck and then clathrin prior to actin polymerization at pedestals during the Nck-dependent pathway of pedestal formation. This study further demonstrates that endocytic proteins are key components of EPEC pedestals and suggests a novel endocytosis subversion strategy employed by these extracellular bacteria.

Atypical roles for Campylobacter jejuni amino acid ATP binding cassette transporter components PaqP and PaqQ in bacterial stress tolerance and pathogen-host cell dynamics.

Campylobacter jejuni is a human pathogen causing severe diarrheal disease; however, our understanding of the survival of C. jejuni during disease and transmission remains limited. Amino acid ATP binding cassette (AA-ABC) transporters in C. jejuni have been proposed as important pathogenesis factors. We have investigated a novel AA-ABC transporter system, encoded by cj0467 to cj0469, by generating targeted deletions of cj0467 (the membrane transport component) and cj0469 (the ATPase component) in C. jejuni 81-176. The analyses described here have led us to designate these genes paqP and paqQ, respectively (pathogenesis-associated glutamine [q] ABC transporter permease [P] and ATPase [Q]). We found that loss of either component resulted in amino acid uptake defects, most notably diminished glutamine uptake. Altered resistance to a series of environmental and in vivo stresses was also observed: both mutants were hyperresistant to aerobic and organic peroxide stress, and while the DeltapaqP mutant was also hyperresistant to heat and osmotic shock, the DeltapaqQ mutant was more susceptible than the wild type to the latter two stresses. The DeltapaqP and DeltapaqQ mutants also displayed a surprising but statistically significant increase in recovery from macrophages and epithelial cells in short-term intracellular survival assays. Annexin V, 4',6-diamidino-2-phenylindole (DAPI), and Western blot analyses revealed that macrophages infected with the DeltapaqP or DeltapaqQ mutant exhibited transient but significant decreases in cell death and extracellular signal-regulated kinase-mitogen-activated protein kinase activation compared to levels in wild-type-infected cells. The DeltapaqP mutant was not defective in either short-term or longer-term mouse colonization, consistent with its increased stress survival and diminished host cell damage phenotypes. Collectively, these results demonstrate a unique correlation of an AA-ABC transporter with bacterial stress tolerances and host cell responses to pathogen infection.

Augmentation of Urinary Lactoferrin Enhances Host Innate Immune Clearance of Uropathogenic Escherichia coli.

Urinary tract infection (UTI) is a prominent global health care burden. Although UTI is readily treated with antibiotics in healthy adults, complicated cases in immune-compromised individuals and the emerging antibiotic resistance of several uropathogens have accelerated the need for new treatment strategies. Here, we surveyed the composition of urinary exosomes in a mouse model of uropathgenic Escherichia coli (UPEC) UTI to identify specific urinary tract defense constituents for therapeutic development. We found an enrichment of the iron-binding glycoprotein lactoferrin in the urinary exosomes of infected mice. In subsequent in vitro studies, we identified human bladder epithelial cells as a source of lactoferrin during UPEC infection. We further established that exogenous treatment with human lactoferrin (hLf) reduces UPEC epithelial adherence and enhances neutrophil antimicrobial functions including bacterial killing and extracellular trap production. Notably, a single intravesicular dose of hLf drastically reduced bladder bacterial burden and neutrophil infiltration in our murine UTI model. We propose that lactoferrin is an important modulator of innate immune responses in the urinary tract and has potential application in novel therapeutic design for UTI.

A group A Streptococcus ADP-ribosyltransferase toxin stimulates a protective interleukin 1ß-dependent macrophage immune response.

UNLABELLED: The M1T1 clone of group A Streptococcus (GAS) is associated with severe invasive infections, including necrotizing fasciitis and septicemia. During invasive M1T1 GAS disease, mutations in the covRS regulatory system led to upregulation of an ADP-ribosyltransferase, SpyA. Surprisingly, a GAS ΔspyA mutant was resistant to killing by macrophages and caused higher mortality with impaired bacterial clearance in a mouse intravenous challenge model. GAS expression of SpyA triggered macrophage cell death in association with caspase-1-dependent interleukin 1ß (IL-1ß) production, and differences between wild-type (WT) and ΔspyA GAS macrophage survival levels were lost in cells lacking caspase-1, NOD-like receptor protein 3 (NLRP3), apoptosis-associated speck-like protein (ASC), or pro-IL-1ß. Similar in vitro findings were identified in macrophage studies performed with pseudomonal exotoxin A, another ADP-ribosylating toxin. Thus, SpyA triggers caspase-1-dependent inflammatory cell death in macrophages, revealing a toxin-triggered IL-1ß-dependent innate immune response pathway critical in defense against invasive bacterial infection. IMPORTANCE: Group A Streptococcus (GAS) is a leading human pathogen capable of producing invasive infections even in healthy individuals. GAS bacteria produce a toxin called SpyA that modifies host proteins through a process called ADP ribosylation. We describe how macrophages, frontline defenders of the host innate immune system, respond to SpyA by undergoing a specialized form of cell death in which they are activated to release the proinflammatory cytokine molecule interleukin 1ß (IL-1ß). Release of IL-1ß activates host immune cell clearance of GAS, as we demonstrated in tissue culture models of macrophage bacterial killing and in vivo mouse infectious-challenge experiments. Similar macrophage responses to a related toxin of Pseudomonas bacteria were also shown. Thus, macrophages recognize certain bacterial toxins to activate a protective immune response in the host.

Myeloid cell sirtuin-1 expression does not alter host immune responses to Gram-negative endotoxemia or Gram-positive bacterial infection.

The role of sirtuin-1 (SIRT1) in innate immunity, and in particular the influence of SIRT1 on antimicrobial defense against infection, has yet to be reported but is important to define since SIRT1 inhibitors are being investigated as therapeutic agents in the treatment of cancer, Huntington's disease, and autoimmune diseases. Given the therapeutic potential of SIRT1 suppression, we sought to characterize the role of SIRT1 in host defense. Utilizing both pharmacologic methods and a genetic knockout, we demonstrate that SIRT1 expression has little influence on macrophage and neutrophil antimicrobial functions. Myeloid SIRT1 expression does not change mortality in gram-negative toxin-induced shock or gram-positive bacteremia, suggesting that therapeutic suppression of SIRT1 may be done safely without suppression of myeloid cell-specific immune responses to severe bacterial infections.

Lack of Tir ubiquitylation contributes to enteropathogenic E. coli remaining extracellular during nonphagocytic cell infections.

Enteropathogenic Escherichia coli (EPEC) is an extracellular pathogen that alters many host subcellular components during its infectious processes. We have previously shown that EPEC hijacks a large assortment of host cell endocytic components and uses these proteins to form protruding structures called "pedestals" rather than triggering internalization of the bacteria. Other invasive pathogens that also recruit similar endocytic components have been shown to enter their host cells on the ubiquitylation of their host cell receptors. Therefore, we hypothesize that EPEC remains extracellular by maintaining its receptor, translocated intimin receptor (Tir), in an unubiquitylated state. Using immunoprecipitation-Western blots, we demonstrate no association of ubiquitin with Tir. To further elucidate the effect Tir ubiquitylation would have on EPEC during their infections, we engineered Tir-ubiquitin fusion constructs, expressed them in host epithelial cells, and infected them with Δtir EPEC. We found these cells induced a significant increase in EPEC invasion as compared with cells that expressed the Tir construct that lacked ubiquitin conjugation. Our results indicate that the lack of EPEC receptor ubiquitylation is a contributing factor that these microbes use to prevent their internalization into epithelial cells.

The Escherichia coli adherence factor plasmid of enteropathogenic Escherichia coli causes a global decrease in ubiquitylated host cell proteins by decreasing ubiquitin E1 enzyme expression through host aspartyl proteases.

Ubiquitylation is a widespread post-translational global regulatory system that is essential for the proper functioning of various cellular events. Recent studies have shown that certain types of Escherichia coli can exploit specific aspects of the ubiquitylation system to influence downstream targets. Despite these findings, examination of the effects pathogenic E. coli have on the overall host ubiquitylation system remain unexplored. To study the impact that pathogenic E. coli have on the ubiquitylation levels of host proteins during infections, we analyzed the entire ubiquitylation system during enteropathogenic E. coli infections of cultured cells. We found that these microbes caused a dramatic decrease in ubiquitylated host proteins during these infections. This occurred with a concomitant reduction in the expression of essential E1 activating enzymes in the host, which are integral for the initiation of the ubiquitylation cascade. Control of host E1 enzyme levels was dependent on the E. coli adherence factor plasmid which acted on host aspartyl proteases within enteropathogenic E. coli. Hijacking of the ubiquitylation system did not require the plasmid-encoded regulator or bundle forming pilus expression, as enteropathogenic E. coli mutated in those factors did not revert the ubiquitylation of host proteins or the abundance of E1 enzyme proteins to uninfected levels. Our work shows that E. coli have developed strategies to usurp post-translational systems by targeting crucial enzymes. The ability of enteropathogenic E. coli to inactivate host protein ubiquitylation could enable more efficient effector protein functionality, providing increased bacterial control of host cells during enteropathogenic E. coli pathogenesis.

AHI-1 interacts with BCR-ABL and modulates BCR-ABL transforming activity and imatinib response of CML stem/progenitor cells.

Chronic myeloid leukemia (CML) represents the first human malignancy successfully treated with a tyrosine kinase inhibitor (TKI; imatinib). However, early relapses and the emergence of imatinib-resistant disease are problematic. Evidence suggests that imatinib and other inhibitors may not effectively eradicate leukemic stem/progenitor cells, and that combination therapy directed to complimentary targets may improve treatment. Abelson helper integration site 1 (Ahi-1)/AHI-1 is a novel oncogene that is highly deregulated in CML stem/progenitor cells where levels of BCR-ABL transcripts are also elevated. Here, we demonstrate that overexpression of Ahi-1/AHI-1 in murine and human hematopoietic cells confer growth advantages in vitro and induce leukemia in vivo, enhancing effects of BCR-ABL. Conversely, RNAi-mediated suppression of AHI-1 in BCR-ABL-transduced lin(-)CD34(+) human cord blood cells and primary CML stem/progenitor cells reduces their growth autonomy in vitro. Interestingly, coexpression of Ahi-1 in BCR-ABL-inducible cells reverses growth deficiencies exhibited by BCR-ABL down-regulation and is associated with sustained phosphorylation of BCR-ABL and enhanced activation of JAK2-STAT5. Moreover, we identified an AHI-1-BCR-ABL-JAK2 interaction complex and found that modulation of AHI-1 expression regulates phosphorylation of BCR-ABL and JAK2-STAT5 in CML cells. Importantly, this complex mediates TKI response/resistance of CML stem/progenitor cells. These studies implicate AHI-1 as a potential therapeutic target downstream of BCR-ABL in CML.

Occurrence of highly fluoroquinolone-resistant and methicillin-resistant Staphylococcus aureus in domestic animals.

We describe phenotypic and genotypic analyses carried out on multidrug-resistant Staphylococcus aureus isolated from domestic animals. The sequence type ST239 methicillin-resistant Staphylococcus aureus isolated from dogs were highly resistant to fluoroquinolones, and new combinations of GyrA and GrlA mutations were identified. These findings are consistent with a role for animal carriage in the dissemination of important human pathogens in the community.

Desmosomes are unaltered during infections by attaching and effacing pathogens.

The human attaching and effacing (A/E) intestinal pathogens enterohemorrhagic Escherichia coli (EHEC), enteropathogenic E. coli (EPEC), and the murine A/E pathogen Citrobacter rodentium cause serious diarrhea in their hosts. These bacteria alter numerous host cell components, including organelles, the host cell cytoskeleton, and tight junctions during the infectious process. One of the proteins that contribute to the intermediate filament network in host cells, cytokeratin-18, is extensively altered during EPEC infections. Based on this, we tested the hypothesis that desmosomes, the only intercellular junctions that interact with intermediate filaments, are also influenced by A/E pathogen infections. We found that the desmosomal transmembrane proteins desmoglein and desmocollin, as well as the desmosome plaque protein desmoplakin, all remain unchanged during EPEC infection in vitro. This evidence is corroborated by the unaltered localization of desmoglein and desmoplakin in vivo in mice infected with C. rodentium for 7 days. Electron microscopic analysis of 7-day C. rodentium-infected murine colonocytes also show no observable differences in the desmosomes when compared to uninfected controls. Our data suggest that, unlike tight junctions, the desmosome protein levels and localization, as well as desmosome morphology, are unaltered during A/E pathogenesis.

Invasive and adherent bacterial pathogens co-Opt host clathrin for infection.

Infection by the bacterium Listeria monocytogenes depends on host cell clathrin. To determine whether this requirement is widespread, we analyzed infection models using diverse bacteria. We demonstrated that bacteria that enter cells following binding to cellular receptors (termed "zippering" bacteria) invade in a clathrin-dependent manner. In contrast, bacteria that inject effector proteins into host cells in order to gain entry (termed "triggering" bacteria) invade in a clathrin-independent manner. Strikingly, enteropathogenic Escherichia coli (EPEC) required clathrin to form actin-rich pedestals in host cells beneath adhering bacteria, even though this pathogen remains extracellular. Furthermore, clathrin accumulation preceded the actin rearrangements necessary for Listeria entry. These data provide evidence for a clathrin-based entry pathway allowing internalization of large objects (bacteria and ligand-coated beads) and used by "zippering" bacteria as part of a general mechanism to invade host mammalian cells. We also revealed a nonendocytic role for clathrin required for extracellular EPEC infections.