Toidi Adekambi, Chris C. Ibegbu, Stephanie Cagle, Ameeta S. Kalokhe, Yun F. Wang, Yijuan Hu, Cheryl L. Day, Susan M. Ray, Jyothi Rengarajan
Nitric oxide (NO) production is critical for the host defense against intracellular pathogens; however, it is unclear whether NO-dependent control of intracellular organisms depends on cell-intrinsic or cell-extrinsic activity of NO. For example, NO production by infected phagocytes may enable these cells to individually control their pathogen burden. Alternatively, the ability of NO to diffuse across cell membranes might be critical for infection control. Here, using a murine ear infection model, we found that, during infection with the intracellular parasite
Romain Olekhnovitch, Bernhard Ryffel, Andreas J. Müller, Philippe Bousso
Development of host protective immunity against
Roanne Keeton, Nasiema Allie, Ivy Dambuza, Brian Abel, Nai-Jen Hsu, Boipelo Sebesho, Philippa Randall, Patricia Burger, Elizabeth Fick, Valerie F.J. Quesniaux, Bernhard Ryffel, Muazzam Jacobs
Biofilms are surface-attached agglomerations of microorganisms embedded in an extracellular matrix. Biofilm-associated infections are difficult to eradicate and represent a significant reservoir for disseminating and recurring serious infections. Infections involving biofilms frequently develop on indwelling medical devices in hospitalized patients, and Staphylococcus epidermidis is the leading cause of infection in this setting. However, the molecular determinants of biofilm dissemination are unknown. Here we have demonstrated that specific secreted, surfactant-like S. epidermidis peptides — the β subclass of phenol-soluble modulins (PSMs) — promote S. epidermidis biofilm structuring and detachment in vitro and dissemination from colonized catheters in a mouse model of device-related infection. Our study establishes in vivo significance of biofilm detachment mechanisms for the systemic spread of biofilm-associated infection and identifies the effectors of biofilm maturation and detachment in a premier biofilm-forming pathogen. Furthermore, by demonstrating that antibodies against PSMβ peptides inhibited bacterial spread from indwelling medical devices, we have provided proof of principle that interfering with biofilm detachment mechanisms may prevent dissemination of biofilm-associated infection.
Rong Wang, Burhan A. Khan, Gordon Y. C. Cheung, Thanh-Huy L. Bach, Max Jameson-Lee, Kok-Fai Kong, Shu Y. Queck, Michael Otto
Sickle cell disease (SCD) is characterized by intravascular hemolysis and inflammation coupled to a 400-fold greater incidence of invasive pneumococcal infection resulting in fulminant, lethal pneumococcal sepsis. Mechanistically, invasive infection is facilitated by a proinflammatory state that enhances receptor-mediated endocytosis of pneumococci into epithelial and endothelial cells. As statins reduce chronic inflammation, in addition to their serum cholesterol-lowering effects, we hypothesized that statin therapy might improve the outcome of pneumococcal infection in SCD. In this study, we tested this hypothesis in an experimental SCD mouse model and found that statin therapy prolonged survival following pneumococcal challenge. The protective effect resulted in part from decreased platelet-activating factor receptor expression on endothelia and epithelia, which led to reduced bacterial invasion. An additional protective effect resulted from inhibition of host cell lysis by pneumococcal cholesterol-dependent cytotoxins (CDCs), including pneumolysin. We conclude therefore that statins may be of prophylactic benefit against invasive pneumococcal disease in patients with SCD and, more broadly, in settings of bacterial pathogenesis driven by receptor-mediated endocytosis and the CDC class of toxins produced by Gram-positive invasive bacteria.
Jason W. Rosch, Angela R. Boyd, Ernesto Hinojosa, Tamara Pestina, Yunming Hu, Derek A. Persons, Carlos J. Orihuela, Elaine I. Tuomanen
Candida parapsilosis is a major cause of human disease, yet little is known about the pathogen’s virulence. We have developed an efficient gene deletion system for C. parapsilosis based on the repeated use of the dominant nourseothricin resistance marker (caSAT1) and its subsequent deletion by FLP-mediated, site-specific recombination. Using this technique, we deleted the lipase locus in the C. parapsilosis genome consisting of adjacent genes CpLIP1 and CpLIP2. Additionally we reconstructed the CpLIP2 gene, which restored lipase activity. Lipolytic activity was absent in the null mutants, whereas the WT, heterozygous, and reconstructed mutants showed similar lipase production. Biofilm formation was inhibited with lipase-negative mutants and their growth was significantly reduced in lipid-rich media. The knockout mutants were more efficiently ingested and killed by J774.16 and RAW 264.7 macrophage-like cells. Additionally, the lipase-negative mutants were significantly less virulent in infection models that involve inoculation of reconstituted human oral epithelium or murine intraperitoneal challenge. These studies represent what we believe to be the first targeted disruption of a gene in C. parapsilosis and show that C. parapsilosis–secreted lipase is involved in disease pathogenesis. This efficient system for targeted gene deletion holds great promise for rapidly enhancing our knowledge of the biology and virulence of this increasingly common invasive fungal pathogen.
Attila Gácser, David Trofa, Wilhelm Schäfer, Joshua D. Nosanchuk
Mucormycosis causes mortality in at least 50% of cases despite current first-line therapies. Clinical and animal data indicate that the presence of elevated available serum iron predisposes the host to mucormycosis. Here we demonstrate that deferasirox, an iron chelator recently approved for use in humans by the US FDA, is a highly effective treatment for mucormycosis. Deferasirox effectively chelated iron from Rhizopus oryzae and demonstrated cidal activity in vitro against 28 of 29 clinical isolates of Mucorales at concentrations well below clinically achievable serum levels. When administered to diabetic ketoacidotic or neutropenic mice with mucormycosis, deferasirox significantly improved survival and decreased tissue fungal burden, with an efficacy similar to that of liposomal amphotericin B. Deferasirox treatment also enhanced the host inflammatory response to mucormycosis. Most importantly, deferasirox synergistically improved survival and reduced tissue fungal burden when combined with liposomal amphotericin B. These data support clinical investigation of adjunctive deferasirox therapy to improve the poor outcomes of mucormycosis with current therapy. As iron availability is integral to the pathogenesis of other infections (e.g., tuberculosis, malaria), broader investigation of deferasirox as an antiinfective treatment is warranted.
Ashraf S. Ibrahim, Teclegiorgis Gebermariam, Yue Fu, Lin Lin,, Mohamed I. Husseiny, Samuel W. French, Julie Schwartz, Christopher D. Skory, John E. Edwards Jr., Brad J. Spellberg
Philipp C. Rittershaus, Talar B. Kechichian, Jeremy C. Allegood, Alfred H. Merrill, Mirko Hennig, Chiara Luberto, Maurizio Del Poeta
The study of regulatory networks in human pathogens such as Cryptococcus neoformans provides insights into host-pathogen interactions that may allow for correlation of gene expression patterns with clinical outcomes. In the present study, deletion of the cryptococcal copper-dependent transcription factor 1 (Cuf1) led to defects in growth and virulence factor expression in low copper conditions. In mouse models, cuf1Δ strains exhibited reduced dissemination to the brain, but no change in lung growth, suggesting copper is limiting in neurologic infections. To examine this further, a biologic probe of available copper was constructed using the cryptococcal CUF1-dependent copper transporter, CTR4. Fungal cells demonstrated high CTR4 expression levels after phagocytosis by macrophage-like J774.16 cells and during infection of mouse brains, but not lungs, consistent with limited copper availability during neurologic infection. This was extended to human brain infections by demonstrating CTR4 expression during C. neoformans infection of an AIDS patient. Moreover, high CTR4 expression by cryptococcal strains from 24 solid organ transplant patients was associated with dissemination to the CNS. Our results suggest that copper acquisition plays a central role in fungal pathogenesis during neurologic infection and that measurement of stable traits such as CTR4 expression may be useful for risk stratification of individuals with cryptococcosis.
Scott R. Waterman, Moshe Hacham, Guowu Hu, Xudong Zhu, Yoon-Dong Park, Soowan Shin, John Panepinto, Tibor Valyi-Nagy, Craig Beam, Shahid Husain, Nina Singh, Peter R. Williamson
Pseudomonas aeruginosa, an important cause of opportunistic infections in humans, delivers bacterial cytotoxins by type III secretion directly into the host cell cytoplasm, resulting in disruption of host cell signaling and host innate immunity. However, little is known about the fate of the toxins themselves following injection into the host cytosol. Here, we show by both in vitro and in vivo studies that the host ubiquitin ligase Cbl-b interacts with the type III–secreted effector exotoxin T (ExoT) and plays a key role in vivo in limiting bacterial dissemination mediated by ExoT. We demonstrate that, following polyubiquitination, ExoT undergoes regulated proteasomal degradation in the host cell cytosol. ExoT interacts with the E3 ubiquitin ligase Cbl-b and Crk, the substrate for the ExoT ADP ribosyltransferase (ADPRT) domain. The efficiency of degradation is dependent upon the activity of the ADPRT domain. In mouse models of acute pneumonia and systemic infection, Cbl-b is specifically required to limit the dissemination of ExoT-producing bacteria whereas c-Cbl plays no detectable role. To the best of our knowledge, this represents the first identification of a mammalian gene product that is specifically required for in vivo resistance to disease mediated by a type III–secreted effector.
Priya Balachandran, Leonard Dragone, Lynne Garrity-Ryan, Armando Lemus, Arthur Weiss, Joanne Engel
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