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Biomedical subjects

R G Washburn

Publications and source records attributed to R G Washburn.

At least 19 recordsLinked to original sources
PubMed1998

Cryptococcal pneumonia complicating pregnancy.

In the present report we describe 4 previously healthy women who developed cryptococcal pneumonia during pregnancy, and 1 pregnant woman with cryptococcal meningitis. These cases illustrate a previously uncharacterized spectrum of cryptococcal disease. We also discuss 24 patients previously reported who had cryptococcal meningitis during pregnancy. Finally, we review the available data for each therapeutic option and present an algorithm for management based on appraisals of disease severity and risk to the unborn fetus. This report emphasizes the need for heightened awareness of cryptococcosis in the differential diagnosis of pneumonia, chest pain, and hypoxemia in the pregnant patient, but at present, there are insufficient epidemiologic data to determine whether incidences of pulmonary or disseminated cryptococcosis actually increase during pregnancy. The risk of congenital cryptococcosis to the unborn fetus is low, and the most likely mechanism whereby neonates acquire invasive fungal pulmonary infection is through aspiration. While it is unclear whether there is any real increased risk of spontaneous abortion or premature labor, the data indicate that overall fetal outcome depends on effective treatment of maternal infection. For patients with dense air-space consolidation, progressive pulmonary disease, or dissemination, antifungal therapy is necessary. Optimal treatment is determined by the acuity and severity of the clinical presentation. Amphotericin B (approximately 1 g) with or without flucytosine represents the choice for initial treatment of the more acutely ill patient with disseminated or progressive pulmonary cryptococcosis who requires hospitalization (whether during or after pregnancy). Oral fluconazole appears to be safe and effective alternative therapy after delivery for the less severely ill patient who can be managed on an outpatient basis. While the use of fluconazole during pregnancy generally appears safe in terms of fetal outcome (49, 58), the class C status and single report of fetal malformation (62) preclude confident recommendation for its use during pregnancy. The risks and benefits of this effective and generally less toxic drug should be discussed with the parents and weighed against the use of amphotericin B. For pregnant women with limited pulmonary cryptococcosis (segmental or nodular infiltrates) and no evidence of dissemination, we recommend close follow-up without antifungal therapy similar to the recommendation for normal hosts with minimal disease. However, it is important to note that there is no extensive experience upon which to base this recommendation for pregnant individuals (45, 55, 103, 108). It is prudent to use frequent physical examinations (for example, every 1-2 months), combined with chest roentgenograms and serum cryptococcal antigens to monitor progression and/or development of disease in both the mother and child for approximately 6 months postpartum. In conclusion, cryptococcosis during pregnancy presents a special challenge to the clinician. A balanced therapeutic approach holds great promise for successful maternal and fetal outcomes.

Adult↗
PubMed1998

The developmentally regulated alb1 gene of Aspergillus fumigatus: its role in modulation of conidial morphology and virulence.

Aspergillus fumigatus, an important opportunistic pathogen which commonly affects neutropenic patients, produces conidia with a bluish-green color. We identified a gene, alb1, which is required for conidial pigmentation. The alb1 gene encodes a putative polyketide synthase, and disruption of alb1 resulted in an albino conidial phenotype. Expression of alb1 is developmentally regulated, and the 7-kb transcript is detected only during the conidiation stage. The alb1 mutation was found to block 1,3,6,8-tetrahydroxynaphthalene production, indicating that alb1 is involved in dihydroxynaphthalene-melanin biosynthesis. Scanning electron microscopy studies showed that the alb1 disruptant exhibited a smooth conidial surface, whereas complementation of the alb1 deletion restored the echinulate wild-type surface. Disruption of alb1 resulted in a significant increase in C3 binding on conidial surfaces, and the conidia of the alb1 disruptant were ingested by human neutrophils at a higher rate than were those of the wild type. The alb1-complemented strain producing bluish-green conidia exhibited inefficient C3 binding and neutrophil-mediated phagocytosis quantitatively similar to those of the wild type. Importantly, the alb1 disruptant had a statistically significant loss of virulence compared to the wild-type and alb1-complemented strains in a murine model. These results suggest that disruption of alb1 causes pleiotropic effects on conidial morphology and fungal virulence.

Amino Acid Sequence↗
PubMed1998

Fungal sinusitis.

Noninvasive fungal sinusitis usually occurs in individuals with a poorly draining maxillary sinus. The infection can be cured by surgical removal of the hyphal mass. In contrast, allergic fungal sinusitis is an upper respiratory disease with an immunopathology similar to that of allergic bronchopulmonary aspergillosis. Surgical debridement and therapy with topical or systemic steroids are recommended. Acute and chronic invasive fungal sinusitis are extremely serious infections requiring aggressive therapy, including extensive surgical debridement and appropriate antifungal chemotherapy. For acute invasive fungal sinusitis in the neutropenic host, survival depends chiefly on bone marrow recovery.

Humans↗
PubMed1997

Aspergillus fumigatus arp1 modulates conidial pigmentation and complement deposition.

Aspergillus fumigatus is an important pathogen causing invasive pulmonary aspergillosis in immunocompromised patients. The fungus propagates by conidia, which are the infectious structures inhaled by the human host. Opsonophagocytosis is thought to contribute to clearance of the inhaled conidia, a process that is facilitated by complement deposition on conidial surfaces. We now show that conidial colour mutants exhibit significant increases in C3 binding capacity compared with wild type. A reddish-pink mutation that led to enhanced C3 binding was complemented by a cosmid clone. A 3.3 kb DNA fragment from the subsequently rescued cosmid was sufficient to restore the bluish-green conidial pigment. The bluish-green transformant exhibited a level of C3 binding similar to that of the parental strain. A gene, designated arp1, was responsible for the complementation. Comparison of the genomic and cDNA sequences of arp1 revealed that it has two introns and encodes a putative protein of 168 amino acids. Arp1 is very similar to scytalone dehydratase, an enzyme involved in 1,8-dihydroxynaphthalene-melanin synthesis in Colletotrichum lagenarium and Magnaporthe grisea. Northern hybridization analysis revealed that arp1 is developmentally regulated, being expressed during conidiation. Disruption of arp1 resulted in reddish-pink conidia and increased C3 binding. Our studies suggest that arp1 modulates the bluish-green pigmentation of conidia as well as complement deposition.

Amino Acid Sequence↗
PubMed1997

Binding and germination of Aspergillus fumigatus conidia on cultured A549 pneumocytes.

Invasive pulmonary aspergillosis is acquired through inhalation of conidia. Little is known about early interactions between Aspergillus fumigatus conidia and alveolar epithelial cells, so an in vitro model was developed to study binding between conidia and A549 cells, a line of type II pneumocytes. Conidia rapidly became attached to confluent monolayers of A549 cells in serum-free medium, reaching a plateau within 40 min. Scanning electron microscopy (EM) showed a random pattern of early adherence; viable conidia subsequently became clustered on pneumocyte surfaces. Following germination of pneumocyte-adherent conidia for 12 h, direct penetration of epithelial cells by hyphae could be demonstrated by scanning and transmission EM. These data suggest that an early event following inhalation of A. fumigatus conidia may be binding of conidia to pneumocytes, followed by hyphal penetration of the epithelial cell layer.

Aspergillus fumigatus↗
PubMed1997

Invasive aspergillosis in mice immunosuppressed with cyclosporin A, tacrolimus (FK506), or sirolimus (rapamycin).

Cyclosporin A, tacrolimus, and sirolimus are immunosuppressive agents initially described as antifungal compounds with different activities for Aspergillus species. The outcome of invasive aspergillosis in mice treated with each agent was investigated in outbred CD-1 mice. Immunosuppressant or vehicle alone was administered from days -1 to +14. Mice were infected on day 0 with resting Aspergillus conidia via lateral tail vein injection. Survival was significantly greater with most regimens than for mice treated with cyclosporin A (100 mg/kg/day; median survival, 3 days): tacrolimus, 1 mg/kg/day (6.5 days, P = .003); sirolimus, 1 or 10 mg/kg/day (7.5 and 9.5 days, respectively; P = .002 and .0001); and vehicle alone (6.5 days, P = .001). However, mice treated with 10 mg/kg/day of tacrolimus survived a median of 4.5 days (P = .25). Survival in the 10-mg sirolimus group did not differ from that of mice given vehicle alone (P = .55). Histologic evaluation suggested the improved survival with tacrolimus and sirolimus may be due in part to direct anti-Aspergillus activity.

Animals↗
PubMed1996

Susceptibility of Helicobacter pylori to the bactericidal activity of human serum.

BACKGROUND: Human serum represents an important barrier to the entry of most mucosal organisms into tissues and to the systemic circulation. If at all present, Helicobacter pylori within gastric tissue is rare, and bacteremia for this organism has been described only once. METHODS: To assess the susceptibility of H. pylori to the bactericidal activity present in normal human serum (NHS), we examined 13 H. pylori isolates. To assess the contributions of the classical and alternative complement pathways to killing, we added either C2-deficient or factor B-deficient serum, respectively, to heat-inactivated NHS. Also we assessed the ability of the strains to bind 125I-C3. RESULTS: After incubation for 60 minutes at 37 degrees C, all 13 H. pylori strains were killed by NHS; heating to 56 degrees C for 30 minutes ablated killing, indicating complement dependence for this phenomenon. In the absence of an antibody source, there was no killing when either an alternative or classical complement pathway source was used. Adding B-deficient serum to heat-inactivated normal human serum did not restore killing, but adding C2-deficient serum permitted partial killing. All of the 13 strains bound 125I-C3. Although the kinetics varied from strain to strain, C3 bound was significantly correlated (r = 0.61, p = 0.03) with serum susceptibility. CONCLUSIONS: H. pylori are susceptible to complement, alternative pathway activation appears critical, and C3 binding is a major locus of variability.

Antibodies, Bacterial↗
PubMed1996

Hyaluronate capsule and surface M protein in resistance to opsonization of group A streptococci.

The major virulence determinant of group A streptococci is the ability to resist opsonization and phagocytic ingestion. The present studies were performed to compare the mechanisms of resistance to opsonization of type 18 and type 24 streptococci and to determine the relative roles of M protein-fibrinogen interaction and the hyaluronate capsule in preventing phagocytic ingestion and killing. By use of parent strains and acapsular transposon mutants in the presence and absence of fibrinogen, we show that type 18 and type 24 streptococci rely on somewhat different mechanisms for resistance to opsonization. Type 24 streptococci bound fibrinogen avidly to their surfaces, and encapsulated organisms were completely resistant to opsonization only in the presence of fibrinogen. In contrast, type 18 streptococci bound 10-fold less fibrinogen than type 24 streptococci and were fully resistant to phagocytosis only when they expressed capsule. The general structural characteristics of the amino-terminal halves of type 18 and type 24 M proteins differed in that type 18 M protein contained only one complete B repeat, whereas type 24 M protein contained five complete B repeats, a structural difference which could potentially be related to the differences in fibrinogen binding between the two serotypes. Immunofluorescence assays of complement deposition were used in combination with 125I-C3 binding assays to show that encapsulated type 24 streptococci were fully resistant to opsonization by C3 only in the presence of plasma. Encapsulated and unencapsulated type 18 streptococci were equally opsonized by C3 in either plasma or serum, yet only encapsulated organisms resisted phagocytic killing in blood. The results of this study indicate that opsonization by C3 does not necessarily lead to phagocytic ingestion and that the hyaluronate capsule and M proteins are variably important in resistance to different group A streptococci to opsonization and phagocytic killing.

Antigens, Bacterial↗
PubMed1995

Intravascular catheter exchange and duration of candidemia. NIAID Mycoses Study Group and the Candidemia Study Group.

During a comparative trial of amphotericin B vs. fluconazole for treatment of candidemia in nonneutropenic patients, data on the management of intravascular catheters were collected. Complete records were available for 91% of the 206 study patients. For the subset of patients with a catheter in place at the time of their first positive blood culture, removal and replacement of all intravascular catheters without exchange over a guidewire from a preexisting line on or before the first day the study drug was administered were associated with a reduction in the subsequent mean duration (+/- SE) of candidemia, from 5.6 +/ -0.8 days to 2.6 +/- 0.5 days (P < .001).

Amphotericin B↗
PubMed1995

Anticryptococcal activity of NK cell-enriched peripheral blood lymphocytes from human immunodeficiency virus-infected subjects: responses to interleukin-2, interferon-gamma, and interleukin-12.

Anticryptococcal activity of highly purified NK cells from patients with either early asymptomatic or late-stage human immunodeficiency virus (HIV) infection proved to be markedly impaired; activity was reproducibly restored to normal levels by in vitro addition of exogenous interleukin-12 (IL-12). For these highly purified NK cells, responses to IL-2 and interferon-gamma (IFN-gamma) among HIV-infected patients were variable, with only 2 of 8 exhibiting significant responses to IL-2 or IFN-gamma. In contrast, IL-2 and IFN-gamma consistently enhanced anticryptococcal activity of mixed lymphocyte populations, cells that more closely approximate the network likely to be operational in vivo.

Cell Separation↗
PubMed1994

A randomized trial comparing fluconazole with amphotericin B for the treatment of candidemia in patients without neutropenia. Candidemia Study Group and the National Institute.

BACKGROUND: Amphotericin B has long been the standard treatment for candidemia, but its use is complicated by its toxicity. More recently, fluconazole, a water-soluble triazole with activity against candida species and little toxicity, has become available. We conducted a multicenter randomized trial that compared amphotericin B with fluconazole as treatment for candidemia. METHODS: To be eligible, patients had to have a positive blood culture for candida species, a neutrophil count > or = 500 per cubic millimeter, and no major immunodeficiency. Patients were randomly assigned to receive either amphotericin B (0.5 to 0.6 mg per kilogram of body weight per day) or fluconazole (400 mg per day), each continued for at least 14 days after the last positive blood culture. Outcomes were assessed by a group of investigators blinded to treatment assignment. RESULTS: Of the 237 patients enrolled, 206 met all entry criteria. The most common diagnoses were renal failure, nonhematologic cancer, and gastrointestinal disease. There was no statistically significant difference in outcome: of the 103 patients treated with amphotericin B, 81 (79 percent) were judged to have been treated successfully, as were 72 of the 103 patients treated with fluconazole (70 percent P = 0.22; 95 percent confidence interval for the difference, -5 to 23 percent). The bloodstream infection failed to clear in 12 patients in the amphotericin group and 15 in the fluconazole group; the species most commonly associated with failure was Candida albicans. There were 41 deaths in the amphotericin group and 34 deaths in the fluconazole group (P = 0.20). Intravascular catheters appeared to be the most frequent source of candidemia. There was less toxicity with fluconazole than with amphotericin B. CONCLUSIONS: In patients without neutropenia and without major immunodeficiency, fluconazole and amphotericin B are not significantly different in their effectiveness in treating candidemia.

Amphotericin B↗
PubMed1992

Binding of complement to trypomastigotes of a Brazil strain of Trypanosoma cruzi: evidence for heterogeneity within the strain.

Binding of the complement components C3 and C5 to epimastigote and trypomastigote stages of the Brazil strain of Trypanosoma cruzi was examined using radioligand binding and flow cytometric assays. Fibroblast-derived trypomastigotes bound approximately 40% fewer molecules of [125I]C3 per parasite than did epimastigotes. The predominant molecular species of C3 deposited on fibroblast-derived trypomastigotes was the inactive form iC3b. Addition of parasite-specific antisera failed to enhance the number of molecules of [125I]C3 per parasite or the proportion of active to inactive C3b. Flow cytometric studies revealed that only 50% of trypomastigotes (fibroblast-derived or blood-form) bound C3. In contrast to results of the [125I]C3 binding studies, flow cytometric analysis showed that the percentage of trypomastigotes binding C3 actually increased upon incubation with parasite-specific antisera. C5 was found also to bind to only a percentage of trypomastigotes.

Animals↗
PubMed1990

Invasive Aspergillus infections complicating coronary artery bypass grafting.

Endovascular infection with Aspergillus species results in unacceptably high mortality of greater than 80% in most series. Failure to recognize the infection early during its clinical course contributes to its formidable lethality. Blood cultures almost never reveal organisms, as in our Cases 1 and 2. When considering a patient with fever, changing murmur, major systemic emboli, or splenomegaly, and with blood cultures negative for organisms months or even years after cardiac surgery, therefore, the physician should maintain a high index of suspicion for fungal endocarditis. The best opportunity to establish the diagnosis antemortem rests in careful histopathologic and microbiologic examination of infected emboli and vegetations. Most authors agree that a combined approach employing early valve replacement and aggressive antifungal chemotherapy with amphotericin B and perhaps flucytosine or rifampin represents the best option for treatment of endovascular Aspergillus infections.

Aged↗