Analysis of a long-term outbreak of XDR Pseudomonas aeruginosa: a molecular epidemiological study

OBJECTIVES

Here we report on a long-term outbreak from 2009 to 2012 with an XDR Pseudomonas aeruginosa on two wards at a university hospital in southern Germany.

METHODS

Whole-genome sequencing was performed on the outbreak isolates and a core genome was constructed for molecular epidemiological analysis. We applied a time-place-sequence algorithm to improve estimation of transmission probabilities.

RESULTS

By using conventional infection control methods we identified 49 P. aeruginosa strains, including eight environmental isolates that belonged to ST308 (by MLST) and carried the metallo-β-lactamase IMP-8. Phylogenetic analysis on the basis of a non-recombinant core genome that contained 22 outbreak-specific SNPs revealed a pattern of four dominant clades with a strong phylogeographic structure and allowed us to determine the potential temporal origin of the outbreak to July 2008, 1 year before the index case was diagnosed. Superspreaders at the root of clades exhibited a high number of probable and predicted transmissions, indicating their exceptional position in the outbreak.

CONCLUSIONS

Our results suggest that the initial expansion of dominant sublineages was driven by a few superspreaders, while environmental contamination seemed to sustain the outbreak for a long period despite regular environmental control measures.

Effect of metallo-β-lactamase production and multidrug resistance on clinical outcomes in patients with Pseudomonas aeruginosa bloodstream infection: a retrospective cohort study

Background

Blood stream infections (BSI) with Pseudomonas aeruginosa lead to poor clinical outcomes. The worldwide emergence and spread of metallo-β-lactamase (MBL) producing, often multidrug-resistant organisms may further aggravate this problem. Our study aimed to investigate the effect of MBL-producing P. aeruginosa (MBL-PA) and various other resistance phenotypes on clinical outcomes.

Methods

A retrospective cohort study was conducted in three German hospitals. Medical files from 2006 until 2012 were studied, and a number of 113 patients with P. aeruginosa BSI were included. The presence of VIM, IMP and NDM genes was detected using molecular techniques. Genetic relatedness was assessed through multilocus sequence typing (MLST). The effect of resistance patterns or MBL production on clinical outcomes was investigated by using multivariate Cox regression models.

Results

In-hospital mortality was significantly higher in patients with MBL-PA and multidrug-resistant P. aeruginosa. However, neither BSI with MBL-PA nor BSI with various resistance phenotypes of P. aeruginosa were independently associated with mortality or length of hospital stay. In multivariate models, the SAPS II score (HR 1.046), appropriate definitive treatment (HR range 0.25-0.26), and cardiovascular disease (HR range 0.44-0.46) were independent predictors of mortality. Concomitant infections were associated with an excess length of stay (HR < 1).

Conclusions

Medication with appropriate antimicrobial agents at any time during the course of infection remains the key for improving clinical outcomes in patients with P. aeruginosa BSI and should be combined with a strict implementation of routine infection control measures.

[Multiresistant gram-negative bacteria. A bacterial challenge of the twenty-first century]

The incidence of human-pathogenic microorganisms with resistance or even complete insensitivity to broad-spectrum antibiotics is increasing. This poses a serious challenge to infection control in hospitals and to hygiene strategies in clinical areas with critically ill patients, particularly intensive care or transplant units. These microorganisms create problems that are seemingly impossible to solve at present. The management of gram-positive pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) has been facilitated by evidence-based recommendations resulting in a measurable decrease in the incidence of infection and, where treatment is concerned, in a selection of reliably effective drugs for clinicians. However, in the more frequent cases of multiresistant gram-negative (MRGN) pathogens, the only option is the use of poorly defined regimens with older drugs, which carry the risk of serious side effects and organ toxicities. This article presents a comparative analysis of hospital hygiene management for MRSA and MRGN pathogens, pointing out both similarities and features which are unique to MRGN pathogens.

High-throughput-screening-based identification and structure-activity relationship characterization defined (S)-2-(1-aminoisobutyl)-1-(3-chlorobenzyl)benzimidazole as a highly antimycotic agent nontoxic to cell lines

Novel nontoxic (S)-2-aminoalkylbenzimidazole derivatives were found to be effective against Candida spp. at low micromolar concentrations using high-throughput screening with infected HeLa cells. A collection of analogues defined the chemical groups relevant for activity. The most active compound was characterized by transcriptional analysis of the response of C. albicans Sc5314. (S)-2-(1-Aminoisobutyl)-1-(3-chlorobenzyl)benzimidazole had a strong impact on membrane biosynthesis. Testing different clinically relevant pathogenic fungi showed the selectivity of the antimycotic activity against Candida species.

Ulceroglandular tularemia

An increasing number of patients with the zoonosis tularemia have been reported in the last few years in Europe. Tularemia can be divided into different forms depending on its appearance. Tularemia must be considered in the differential diagnosis of diseases that present with an ulcer and regional lymphadenopathy. The diagnosis can be confirmed by culturing Francisella tularensis. With effective antibiotic intervention, the prognosis is favorable. Typically tularemia develops after outdoor activities; it is generally transferred by blood-sucking arthropods from infected wild animals to humans.

[Methicillin-resistant Staphylococcus aureus (MRSA) infections. Epidemiology, diagnostics, therapy, and prevention]

The increasing number of complicated soft-tissue or invasive infections caused by methicillin-resistant Staphylococcus aureus (MRSA) is a frequent reason for elaborate treatment regimens. Unidentified MRSA carriers may be the origin of endemic spread to other patients and medical staff. Recently, community-associated cMRSA with particular virulence factors were isolated from persons without the typical history of hospital contacts. Molecular tools for the timely detection of the mecA resistance gene for the identification of MRSA in medical test specimens have become a standard approach in MRSA-related diagnostic procedures. The actual therapy of MRSA infections requires consideration of both the appropriate spectrum of activity and the adequate pharmacological properties of a chosen antimicrobial. Preventive strategies rely on the consistent application of standard hygiene precautions, which have to be supplemented with increased barriers for the isolation of identified MRSA patients.

Experimental infection of rodent mammals for fungal virulence testing

Invasive fungal infections comprise a group of serious and life-threatening diseases affecting immunocompromised patients. Molecular analysis of fungal virulence involves the deletion of genes that are suspected for contributing to fungal pathogenesis. Phenotypic analysis of the generated mutants includes in vivo infection experiments in order to assign a function during fungal disease to a gene of interest.

Analysis of the Candida albicans - specific T-cell response and oropharyngeal Candida colonization in a cohort of HIV-1-infected patients

To investigate Candida epidemiology and immunologic correlates of protection in HIV-1 infected patients, we analyzed oral Candida colonization in correlation to the Candida-specific T-cell response measured by g-IFN ELISPOT using different Candida (C.) albicans strains. In 16/46 patients (13 asymptomatic, 3 with oral thrush), but in 0/28 controls, Candida (13 C. albicans, 1 C. lusitaniae, 1 C. krusei, 1 C. parapsilosis) was isolated. Candida specific T-cells were detected more frequently in controls (20/28) than in HIV-1+ subjects (16/46, p= 0.03). We observed a significant association of higher CD4 cell numbers with both detection of Candida specific T-cells and lack of oral Candida colonization, but there was no significant correlation of oral Candida colonization to the detection of Candida specific T-cells, viral load or antiretroviral therapy. Thus, local mucosal immunity seems to be more important in the pathogenesis of Candida colonization than circulating Candida specific T-cells. The pathogenic C. albicans strain K24122 was less frequently recognized by patients (6/46) than the laboratory adapted strain SC5314 (14/46, p= 0.03), whereas a similar recognition of both strains was observed in healthy controls. This indicates an impaired Candida-specific T-cell repertoire in HIV+ patients that could increase the risk of immune evasion by C. albicans.

Role of calcineurin in stress resistance, morphogenesis, and virulence of a Candida albicans wild-type strain

By generating a calcineurin mutant of the Candida albicans wild-type strain SC5314 with the help of a new recyclable dominant selection marker, we confirmed that calcineurin mediates tolerance to a variety of stress conditions but is not required for the ability of C. albicans to switch to filamentous growth in response to hypha-inducing environmental signals. While calcineurin was essential for virulence of C. albicans in a mouse model of disseminated candidiasis, deletion of CMP1 did not significantly affect virulence during vaginal or pulmonary infection, demonstrating that the requirement for calcineurin for a successful infection depends on the host niche.

Fungal adenylyl cyclase integrates CO2 sensing with cAMP signaling and virulence

The ascomycete Candida albicans is the most common fungal pathogen in immunocompromised patients . Its ability to change morphology, from yeast to filamentous forms, in response to host environmental cues is important for virulence . Filamentation is mediated by second messengers such as cyclic adenosine 3',5'-monophosphate (cAMP) synthesized by adenylyl cyclase . The distantly related basidiomycete Cryptococcus neoformans is an encapsulated yeast that predominantly infects the central nervous system in immunocompromised patients . Similar to the morphological change in C. albicans, capsule biosynthesis in C. neoformans, a major virulence attribute, is also dependent upon adenylyl cyclase activity . Here we demonstrate that physiological concentrations of CO2/HCO3- induce filamentation in C. albicans by direct stimulation of cyclase activity. Furthermore, we show that CO2/HCO3- equilibration by carbonic anhydrase is essential for pathogenesis of C. albicans in niches where the available CO2 is limited. We also demonstrate that adenylyl cyclase from C. neoformans is sensitive to physiological concentrations of CO2/HCO3-. These data demonstrate that the link between cAMP signaling and CO2/HCO3- sensing is conserved in fungi and reveal CO2 sensing to be an important mediator of fungal pathogenesis. Novel therapeutic agents could target this pathway at several levels to control fungal infections.

Identification and characterization of Cor33p, a novel protein implicated in tolerance towards oxidative stress in Candida albicans

We applied two-dimensional gel electrophoresis to identify downstream effectors of CPH1 and EFG1 under hypha-inducing conditions in Candida albicans. Among the proteins that were expressed in wild-type cells but were strongly downregulated in a cph1Delta/efg1Delta double mutant in alpha-minimal essential medium at 37 degrees C, we could identify not-yet-characterized proteins, including Cor33-1p and Cor33-2p. The two proteins are almost identical (97% identity) and represent products of allelic isoforms of the same gene. Cor33p is highly similar to Cip1p from Candida sp. but lacks any significant homology to proteins from Saccharomyces cerevisiae. Strikingly, both proteins share homology with phenylcoumaran benzylic ether reductases and isoflavone reductases from plants. For other hypha-inducing media, like yeast-peptone-dextrose (YPD) plus serum at 37 degrees C, we could not detect any transcription for COR33 in wild-type cells, indicating that Cor33p is not hypha specific. In contrast, we found a strong induction for COR33 when cells were treated with 5 mM hydrogen peroxide. However, under oxidative conditions, transcription of COR33 was not dependent on EFG1, indicating that other regulatory factors are involved. In fact, upregulation depends on CAP1 at least, as transcript levels were clearly reduced in a Deltacap1 mutant strain under oxidative conditions. Unlike in wild-type cells, transcription of COR33 in a tsa1Delta mutant can be induced by treatment with 0.1 mM hydrogen peroxide. This suggests a functional link between COR33 and thiol-specific antioxidant-like proteins that are important in the oxidative-stress response in yeasts. Concordantly, cor33Delta deletion mutants show retarded growth on YPD plates supplemented with hydrogen peroxide, indicating that COR33 in general is implicated in conferring tolerance toward oxidative stress on Candida albicans.

Induction of SAP7 correlates with virulence in an intravenous infection model of candidiasis but not in a vaginal infection model in mice

SAP7 of Candida albicans is induced after vaginal infection of mice. Conversely, virulence during vaginal infection was not affected in a Deltasap7/Deltasap7 mutant strain. Only a partial virulence phenotype was detectable after intravenous injection. In conclusion, SAP7 expression does not correlate with C. albicans virulence in mice.

The moonlighting protein Tsa1p is implicated in oxidative stress response and in cell wall biogenesis inCandida albicans

Candida albicans is one of the most common fungal pathogens in humans. The cell wall is the first contact site between host and pathogen and thus is critical for colonization and infection of the host. We have identified Tsa1p, a protein that is differentially localized to the cell wall of C. albicans in hyphal cells but remains in the cytosol and nucleus in yeast-form cells. This is different from Saccharomyces cerevisiae, where the homologous protein solely has been found in the cytoplasm. We report here that TSA1 confers resistance towards oxidative stress as well as is involved in the correct composition of hyphal cell walls. However, no significant change of the cell wall composition was observed in a TSA1 deletion strain in yeast-form cells, which is in good agreement with the observation that Tsa1p is absent from the yeast-form cell wall. This indicates that Tsa1p of C. albicans might represent a moonlighting protein with specific functions correlating to its respective localization. Furthermore, the translocation of Tsa1p to the hyphal cell wall of C. albicans depends on Efg1p, suggesting a contribution of the cAMP/PKA pathway to the localization of this protein. In a strain deleted for TUP1 that filaments constitutively Tsa1p can be found in the cell wall under all conditions tested, confirming the result that Tsa1p localization to the cell wall is correlated to the morphology of C. albicans.

PMT family of Candida albicans: five protein mannosyltransferase isoforms affect growth, morphogenesis and antifungal resistance

Protein O-mannosyltransferases (Pmt proteins) initiate O-mannosylation of secretory proteins. The PMT gene family of the human fungal pathogen Candida albicans consists of PMT1 and PMT6, as well as three additional PMT genes encoding Pmt2, Pmt4 and Pmt5 isoforms described here. Both PMT2 alleles could not be deleted and growth of conditional strains, containing PMT2 controlled by the MET3- or tetOScHOP1-promoters, was blocked in non-permissive conditions, indicating that PMT2 is essential for growth. A homozygous pmt4 mutant was viable, but synthetic lethality of pmt4 was observed in combination with pmt1 mutations. Hyphal morphogenesis of a pmt4 mutant was defective under aerobic induction conditions, yet increased in embedded or hypoxic conditions, suggesting a role of Pmt4p-mediated O-glycosylation for environment-specific morphogenetic signalling. Although a PMT5 transcript was detected, a homozygous pmt5 mutant was phenotypically silent. All other pmt mutants showed variable degrees of supersensitivity to antifungals and to cell wall-destabilizing agents. Cell wall composition was markedly affected in pmt1 and pmt4 mutants, showing a significant decrease in wall mannoproteins. In a mouse model of haematogenously disseminated infection, PMT4 was required for full virulence of C. albicans. Functional analysis of the first complete PMT gene family in a fungal pathogen indicates that Pmt isoforms have variable and specific roles for in vitro and in vivo growth, morphogenesis and antifungal resistance.

Profile of Candida albicans-secreted aspartic proteinase elicited during vaginal infection

Vaginal infections caused by the opportunistic yeast Candida albicans are a significant problem in women of child-bearing age. Several factors are recognized as playing a crucial role in the pathogenesis of superficial candidiasis; these factors include hyphal formation, phenotypic switching, and the expression of virulence factors, including a 10-member family of secreted aspartic proteinases. In the present investigation, we analyzed the secreted aspartic proteinase gene (SAP) expression profile of C. albicans that is elicited in the course of vaginal infection in mice and how this in vivo expression profile is associated with hyphal formation. We utilized two different genetic reporter systems that allowed us to observe SAP expression on a single-cell basis, a recombination-based in vivo expression technology and green fluorescent protein-expressing Candida reporter strains. Of the six SAP genes that were analyzed (SAP1 to SAP6), only SAP4 and SAP5 were detectably induced during infection in this model. Expression of both of these genes was associated with hyphal growth, although not all hyphal cells detectably expressed SAP4 and SAP5. SAP5 expression was induced soon after infection, whereas SAP4 was expressed at later times and in fewer cells compared with SAP5. These findings point to a link between morphogenetic development and expression of virulence genes during Candida vaginitis in mice, where host signals induce both hyphal formation and expression of SAP4 and SAP5, but temporal gene expression patterns are ultimately controlled by other factors.

Tec1p-independent activation of a hypha-associated Candida albicans virulence gene during infection

The Tec1p transcription factor is involved in the expression of hypha-specific genes in Candida albicans. Although the induction of the hypha-associated SAP5 gene by serum in vitro depends on Tec1p, deletion of all Tec1p binding site consensus sequences from the SAP5 promoter did not affect its activation. In two different animal models of candidiasis, the SAP5 promoter was induced even in a Deltatec1 deletion mutant, demonstrating that the requirement for Tec1p in gene expression in C. albicans depends on the environmental conditions within the host.

Surveillance of nosocomial transmission of Candida albicans in an intensive care unit by DNA fingerprinting

The frequency of nosocomial transmission of the opportunistic fungal pathogen Candida albicans in an intensive care unit was tested by DNA fingerprinting of 91 isolates from 32 hospitalized patients with the mid-repetitive Ca3 DNA probe. This showed that serial isolates of C. albicans from individual patients belonged to genetically distinct strains. In comparison with nosocomial bacterial pathogens, the transmission of C. albicans in an intensive care unit occurred at a much lower frequency. In conclusion, the threat of C. albicans infection does not lie within the hospital, but in commensal isolates. These findings are relevant for infection control practices.

High diversity of ankA sequences of Anaplasma phagocytophilum among Ixodes ricinus ticks in Germany

In Germany humans with acute granulocytic ehrlichiosis have not yet been described. Here, we characterized three different genes of Anaplasma phagocytophilum strains infecting German Ixodes ricinus ticks in order to test whether they differ from strains in other European countries and the United States. A total of 1,022 I. ricinus ticks were investigated for infection with A. phagocytophilum by nested PCR and sequence analysis. Forty-two (4.1%) ticks were infected. For all positive ticks, parts of the 16S rRNA and groESL genes were sequenced. The complete coding sequence of the ankA gene could be determined in 24 samples. The 16S rRNA and groESL gene sequences were as much as 100% identical to known sequences. Fifteen ankA sequences were >/=99.37% identical to sequences derived from humans with granulocytic ehrlichiosis in Europe and from a horse with granulocytic ehrlichiosis in Germany. Thus, German I. ricinus ticks most likely harbor A. phagocytophilum strains that can cause disease in humans. Nine additional sequences were clearly different from known ankA sequences. Because these newly described sequences have never been obtained from diseased humans or animals, their biological significance is currently unknown. Based on this unexpected sequence heterogeneity, we propose to use the ankA gene for further phylogenetic analyses of A. phagocytophilum and to investigate the biology and pathogenicity of strains that differ in the ankA gene.

Calcineurin is essential for virulence in Candida albicans

Calcineurin is a conserved Ca(2+)-calmodulin-activated, serine/threonine-specific protein phosphatase that regulates a variety of physiological processes, e.g., cell cycle progression, polarized growth, and adaptation to salt and alkaline pH stresses. In the pathogenic yeast Cryptococcus neoformans, calcineurin is also essential for growth at 37 degrees C and virulence. To investigate whether calcineurin plays a role in the virulence of Candida albicans, the major fungal pathogen of humans, we constructed C. albicans mutants in which both alleles of the CMP1 gene, encoding the calcineurin catalytic subunit, were deleted. The C. albicans Delta cmp1 mutants displayed hypersensitivity to elevated Na(+), Li(+), and Mn(2+) concentrations and to alkaline pH, phenotypes that have been described after calcineurin inactivation in the related yeast Saccharomyces cerevisiae. Unlike S. cerevisiae calcineurin mutants, which exhibit reduced susceptibility to high Ca(2+) concentrations, growth of C. albicans was inhibited in the presence of 300 mM CaCl(2) after the deletion of CMP1, demonstrating that there are also differences in calcineurin-mediated cellular responses between these two yeast species. In contrast to C. neoformans, inactivation of calcineurin did not cause temperature sensitivity in C. albicans. In addition, hyphal growth, an important virulence attribute of C. albicans, was not impaired in the Delta cmp1 mutants under a variety of inducing conditions. Nevertheless, the virulence of the mutants was strongly attenuated in a mouse model of systemic candidiasis, demonstrating that calcineurin signaling is essential for virulence in C. albicans.

Signaling through adenylyl cyclase is essential for hyphal growth and virulence in the pathogenic fungus Candida albicans

The human fungal pathogen Candida albicans switches from a budding yeast form to a polarized hyphal form in response to various external signals. This morphogenetic switching has been implicated in the development of pathogenicity. We have cloned the CaCDC35 gene encoding C. albicans adenylyl cyclase by functional complementation of the conditional growth defect of Saccharomyces cerevisiae cells with mutations in Ras1p and Ras2p. It has previously been shown that these Ras homologues regulate adenylyl cyclase in yeast. The C. albicans adenylyl cyclase is highly homologous to other fungal adenylyl cyclases but has less sequence similarity with the mammalian enzymes. C. albicans cells deleted for both alleles of CaCDC35 had no detectable cAMP levels, suggesting that this gene encodes the only adenylyl cyclase in C. albicans. The homozygous mutant cells were viable but grew more slowly than wild-type cells and were unable to switch from the yeast to the hyphal form under all environmental conditions that we analyzed in vitro. Moreover, this morphogenetic switch was completely blocked in mutant cells undergoing phagocytosis by macrophages. However, morphogenetic switching was restored by exogenous cAMP. On the basis of epistasis experiments, we propose that CaCdc35p acts downstream of the Ras homologue CaRas1p. These epistasis experiments also suggest that the putative transcription factor Efg1p and components of the hyphal-inducing MAP kinase pathway depend on the function of CaCdc35p in their ability to induce morphogenetic switching. Homozygous cacdc35 Delta cells were unable to establish vaginal infection in a mucosal membrane mouse model and were avirulent in a mouse model for systemic infections. These findings suggest that fungal adenylyl cyclases and other regulators of the cAMP signaling pathway may be useful targets for antifungal drugs.

Ras links cellular morphogenesis to virulence by regulation of the MAP kinase and cAMP signalling pathways in the pathogenic fungus Candida albicans

The pathogenic fungus Candida albicans is capable of responding to a wide variety of environmental cues with a morphological transition from a budding yeast to a polarized filamentous form. We demonstrate that the Ras homologue of C. albicans, CaRas1p, is required for this morphological transition and thereby contributes to the development of pathogenicity. However, CaRas1p is not required for cellular viability. Deletion of both alleles of the CaRAS1 gene caused in vitro defects in morphological transition that were reversed by either supplementing the growth media with cAMP or overexpressing components of the filament-inducing mitogen-activated protein (MAP) kinase cascade. The induction of filament-specific secreted aspartyl proteinases encoded by the SAP4-6 genes was blocked in the mutant cells. The defects in filament formation were also observed in situ after phagocytosis of C. albicans cells in a macrophage cell culture assay and, in vivo, after infection of kidneys in a mouse model for systemic candidiasis. In the macrophage assay, the mutant cells were less resistant to phagocytosis. Moreover, the defects in filament formation were associated with reduced virulence in the mouse model. These results indicate that, in response to environmental cues, CaRas1p is required for the regulation of both a MAP kinase signalling pathway and a cAMP signalling pathway. CaRas1p-dependent activation of these pathways contributes to the pathogenicity of C. albicans cells through the induction of polarized morphogenesis. These findings elucidate a new medically relevant role for Ras in cellular morphogenesis and virulence in an important human infectious disease.

Suppression of type 2 NO-synthase activity in macrophages by Candida albicans

Macrophages (Mphi) are important for the defence against experimental disseminated candidiasis. Nitric oxide (NO) generated by the inducible isoform of NO-synthase (iNOS or NOS2) is thought to contribute to candidacidal effector functions by activated Mphi. In vitro, however, Mphi cannot control the growth and hyphal formation of Candida (C.) albicans. Using mouse peritoneal exudate Mphi stimulated with IFN-gamma and LPS, we examined the effect of C. albicans on NO synthesis, NOS2 enzyme activity and macrophage survival. C. albicans effectively inhibited the production of NO via suppression of total NOS2 protein and enzyme activity. Hyphal formation of C. albicans and direct interaction with host cells was required for maximum inhibition of NO production, whereas non-filamentous C. albicans mutants released soluble products that effected only partial inhibition. Ultimately, Mphi underwent apoptotic cell death after infection with C. albicans wild-type strains capable of hyphal formation, indicated by loss of the mitochondrial membrane potential and onset of chromatin degradation. NO suppression and Mphi killing are potent activities of C. albicans that may augment virulence of C. albicans.

Repression of hyphal proteinase expression by the mitogen-activated protein (MAP) kinase phosphatase Cpp1p of Candida albicans is independent of the MAP kinase Cek1p

Cpp1p is a putative mitogen-activated protein (MAP) kinase phosphatase that suppresses Candida albicans hyphal formation at 25 degrees C through its probable substrate, the Cek1p filamentation MAP kinase. Here we report that expression of the serum-induced genes SAP4-6 and HYR1 increased several fold in hyphal forms of a cpp1/cpp1 null mutant, while the rate and extent of hyphal development up to 5 h were normal. Therefore, we provide evidence that Cpp1p represses hyphal gene expression by acting through a Cek1p-independent mechanism. SAP4-6 and HYR1 transcripts were undetectable in a null mutant of another key regulator of filamentation, Efg1p; thus, Efg1p and Cpp1p oppose each other during the expression of these genes in hyphal forms.

The TEA/ATTS transcription factor CaTec1p regulates hyphal development and virulence in Candida albicans

The temporal and spatial expression of stage-specific genes during morphological development of fungi and higher eukaryotes is controlled by transcription factors. In this study, we report the cloning and functional analysis of the Candida albicans TEC1 (CaTEC1) gene, a new member of the TEA/ATTS family of transcription factors that regulates C. albicans virulence. The promoters of the type 4, 5 and 6 proteinase isogenes (SAP4-6) contain repetitive TEA/ATTS consensus sequence motifs. This finding suggests a possible role for a homologue of Saccharomyces cerevisiae TEC1 during the activation of proteinase gene expression in C. albicans. CaTEC1 is predominantly expressed in the hyphal form of C. albicans. In vitro, serum-induced hyphal formation as well as evasion from MPhi after phagocytosis is suppressed in catec1/catec1 mutant cells. Furthermore, expression of the proteinase isogenes SAP4-6 is no longer inducible in these mutant cells. The deletion of the CaTEC1 gene attenuates virulence of C. albicans in a systemic model of murine candidiasis, although both mutant and revertant cells that were prepared from infected tissues or the vaginal mucosa grew in a hyphal morphology in vivo. CaTEC1 complements the pseudohyphal and invasive growth defect of haploid and diploid S. cerevisiae tec1/tec1 mutant cells and strongly activates the promoter of FLO11, a gene required for pseudohyphal growth. This study provides the first evidence pointing to an essential role for a member of the TEA/ATTS transcription factor family that had so far only been ascribed to function during development as a virulence regulator in microbial pathogenesis.

Morphogenesis, adhesive properties, and antifungal resistance depend on the Pmt6 protein mannosyltransferase in the fungal pathogen candida albicans

Protein mannosyltransferases (Pmt proteins) initiate O glycosylation of secreted proteins in fungi. We have characterized PMT6, which encodes the second Pmt protein of the fungal pathogen Candida albicans. The residues of Pmt6p are 21 and 42% identical to those of C. albicans Pmt1p and S. cerevisiae Pmt6p, respectively. Mutants lacking one or two PMT6 alleles grow normally and contain normal Pmt enzymatic activities in cell extracts but show phenotypes including a partial block of hyphal formation (dimorphism) and a supersensitivity to hygromycin B. The morphogenetic defect can be suppressed by overproduction of known components of signaling pathways, including Cek1p, Cph1p, Tpk2p, and Efg1p, suggesting a specific Pmt6p target protein upstream of these components. Mutants lacking both PMT1 and PMT6 are viable and show pmt1 mutant phenotypes and an additional sensitivity to the iron chelator ethylenediamine-di(o-hydroxyphenylacetic acid). The lack of Pmt6p significantly reduces adherence to endothelial cells and overall virulence in a mouse model of systemic infection. The results suggest that Pmt6p regulates a more narrow subclass of proteins in C. albicans than Pmt1p, including secreted proteins responsible for morphogenesis and antifungal sensitivities.

Volatile anesthetics differentially affect immunostimulated expression of inducible nitric oxide synthase: role of intracellular calcium

BACKGROUND

Nitric oxide released by inducible nitric oxide synthase (iNOS) plays an important role in immune responses and systemic vasodilation in septic shock. Volatile anesthetics have been reported to interfere with signal transduction and gene expression. We studied the effect of volatile anesthetics on activity and expression of iNOS and potential mechanisms of action.

METHODS

Nitrite release and iNOS expression were determined using the Griess reaction and Western and Northern blot techniques, respectively, in J774 murine macrophages stimulated with lipopolysaccharide and gamma-interferon in the absence and presence of various concentrations (0.25-2.0 minimum alveolar concentration [MAC]) of volatile anesthetics (i.e., halothane, enflurane, isoflurane, desflurane). Furthermore, potential interference of volatile anesthetics with specific signal transduction pathways was investigated.

RESULTS

All volatile anesthetics, studied in a time- and dose-dependent manner, suppressed nitrite production and iNOS expression in J774 macrophages stimulated by lipopolysaccharide or gamma-interferon at clinically relevant concentrations. The inhibition was completely antagonized by ionomycin but unaffected by diacylglycerol, phorbol myristate acetate, and C2-ceramide. In contrast, in cells costimulated by lipopolysaccharide plus gamma-interferon, volatile anesthetics significantly increased nitrite production and iNOS expression independent of ionomycin and other mediators studied.

CONCLUSIONS

Volatile anesthetics strongly reduced the mRNA and protein levels of iNOS and NOS activity after a single stimulation with lipopolysaccharide or gamma-interferon, most likely by attenuating intracellular calcium increase. Costimnulation with lipopolysaccharide plus gamma-interferon, however, results in maximum iNOS expression and activity, which are no longer inhibited but are potentiated by volatile anesthetics by unidentified mechanisms.

Coiling phagocytosis of trypanosomatids and fungal cells

Coiling phagocytosis has previously been studied only with the bacteria Legionella pneumophila and Borrelia burgdorferi, and the results were inconsistent. To learn more about this unconventional phagocytic mechanism, the uptake of various eukaryotic microorganisms by human monocytes, murine macrophages, and murine dendritic cells was investigated in vitro by video and electron microscopy. Unconventional phagocytosis of Leishmania spp. promastigotes, Trypanosoma cruzi trypomastigotes, Candida albicans hyphae, and zymosan particles from Saccharomyces cerevisiae differed in (i) morphology (rotating unilateral pseudopods with the trypanosomatids, overlapping bilateral pseudopods with the fungi), (ii) frequency (high with Leishmania; occasional with the fungi; rare with T. cruzi), (iii) duration (rapid with zymosan; moderate with the trypanosomatids; slow with C. albicans), (iv) localization along the promastigotes (flagellum of Leishmania major and L. aethiopica; flagellum or posterior pole of L. donovani), and (v) dependence on complement (strong with L. major and L. donovani; moderate with the fungi; none with L. aethiopica). All of these various types of unconventional phagocytosis gave rise to similar pseudopod stacks which eventually transformed to a regular phagosome. Further video microscopic studies with L. major provided evidence for a cytosolic localization, synchronized replication, and exocytic release of the parasites, extending traditional concepts about leishmanial infection of host cells. It is concluded that coiling phagocytosis comprises phenotypically similar consequences of various disturbances in conventional phagocytosis rather than representing a single separate mechanism.

Roles of the Candida albicans mitogen-activated protein kinase homolog, Cek1p, in hyphal development and systemic candidiasis

Extracellular signal-regulated protein kinase (ERK, or mitogen-activated protein kinase [MAPK]) regulatory cascades in fungi turn on transcription factors that control developmental processes, stress responses, and cell wall integrity. CEK1 encodes a Candida albicans MAPK homolog (Cek1p), isolated by its ability to interfere with the Saccharomyces cerevisiae MAPK mating pathway. C. albicans cells with a deletion of the CEK1 gene are defective in shifting from a unicellular budding colonial growth mode to an agar-invasive hyphal growth mode when nutrients become limiting on solid medium with mannitol as a carbon source or on glucose when nitrogen is severely limited. The same phenotype is seen in C. albicans mutants in which the homologs (CST20, HST7, and CPH1) of the S. cerevisiae STE20, STE7, and STE12 genes are disrupted. In S. cerevisiae, the products of these genes function as part of a MAPK cascade required for mating and invasiveness of haploid cells and for pseudohyphal development of diploid cells. Epistasis studies revealed that the C. albicans CST20, HST7, CEK1, and CPH1 gene products lie in an equivalent, canonical, MAPK cascade. While Cek1p acts as part of the MAPK cascade involved in starvation-specific hyphal development, it may also play independent roles in C. albicans. In contrast to disruptions of the HST7 and CPH1 genes, disruption of the CEK1 gene adversely affects the growth of serum-induced mycelial colonies and attenuates virulence in a mouse model for systemic candidiasis.

Derepressed hyphal growth and reduced virulence in a VH1 family-related protein phosphatase mutant of the human pathogen Candida albicans

Mitogen-activated protein (MAP) kinases are pivotal components of eukaryotic signaling cascades. Phosphorylation of tyrosine and threonine residues activates MAP kinases, but either dual-specificity or monospecificity phosphatases can inactivate them. The Candida albicans CPP1 gene, a structural member of the VH1 family of dual- specificity phosphatases, was previously cloned by its ability to block the pheromone response MAP kinase cascade in Saccharomyces cerevisiae. Cpp1p inactivated mammalian MAP kinases in vitro and acted as a tyrosine-specific enzyme. In C. albicans a MAP kinase cascade can trigger the transition from the budding yeast form to a more invasive filamentous form. Disruption of the CPP1 gene in C. albicans derepressed the yeast to hyphal transition at ambient temperatures, on solid surfaces. A hyphal growth rate defect under physiological conditions in vitro was also observed and could explain a reduction in virulence associated with reduced fungal burden in the kidneys seen in a systemic mouse model. A hyper-hyphal pathway may thus have some detrimental effects on C. albicans cells. Disruption of the MAP kinase homologue CEK1 suppressed the morphological effects of the CPP1 disruption in C. albicans. The results presented here demonstrate the biological importance of a tyrosine phosphatase in cell-fate decisions and virulence in C. albicans.

A novel repeat sequence (CKRS-1) containing a tandemly repeated sub-element (kre) accounts for differences between Candida krusei strains fingerprinted with the probe CkF1,2

CkF1,2 has been reported as an effective DNA fingerprinting probe of Candida krusei. It is composed of two genomic EcoRI-restriction fragments, F1 and F2, which are approximately 5.4 and 5.2 kb, respectively. Sequence analysis of F1 reveals that it is 5261 bp-long, has a GC content of 42.2 mol%, and originates from the intergenic region of the ribosomal RNA cistrons (IGR). F1 comprises 488 bp of the 3' end of a 25s rRNA gene, a non-transcribed spacer region 1 (NTS1), a 5s gene (121 bp), and a major portion of the non-transcribed spacer region 2 (NTS2). A 1256 bp-long repeated sequence, CKRS-1, with a GC content of 35 mol%, has been identified in NTS2. CKRS-1 contains eight tandemly repeated sub-elements, kre-0 to kre-7. The first two, kre-0 and kre-1, are 164 bp-long, the next five sub-elements, kre-2 to kre-6, are 165 bp-long, and the last element, kre-7, is 103 bp-long. The eight sub-elements share nucleotide-sequence homologies between 66 to 100%, with kre-2, kre-3 and kre-4 identical, and kre-0 the most divergent. Shorter repeated sequences were also identified in three regions of F1, which were named domains "a", "b" and "c". Restriction mapping, cross hybridization, and direct comparison of sequences show that F1 and F2 are polymophic forms of the IGR and their size difference is due both to the number of kre sub-elements in CKRS-1 and to a 24-bp deletion in domain "b". While F1 contains eight kre sub-elements, F2 contains seven. In C. krusei strain K31, four polymorphic forms of CKRS-1 have been identified containing five, six, seven and eight kre sub-elements. CKRS-1 is dispersed on three of the chromosomes of highest molecular weights separated by transverse alternating-field electrophoresis. CKRS-1 does not hybridize significantly to any transcription product. Polymorphisms in single DNA fingerprints and differences between the DNA fingerprints of strains of C. krusei based upon CkF1,2 hybridization patterns therefore appear to be based, at least in part, on the variable number of tandemly repeated kre sub-elements in CKRS-1.

Development of two species-specific fingerprinting probes for broad computer-assisted epidemiological studies of Candida tropicalis

Candida tropicalis has emerged as the second most frequent colonizing Candida species, and it has been documented in nosocomial infections. To develop an effective fingerprinting system for this species, which is amenable to computer-assisted analyses and which provides information on the genetic relatedness of independent isolates, two DNA fragments, Ct3 (18,000 bp) and Ct14 (20,000 bp), were cloned from a genomic library of Sau3AI partial digestion products. Both probes generate complex Southern blot patterns containing 8 to 20 bands, when hybridized to EcoRI- or EcoRI-HaeIII-digested DNA of independent C. tropicalis isolates. The two probes show no cross-hybridization and are both species specific for C. tropicalis. A comparison of the capacity of the two probes to identify the same strain in different isolates, and differentiate unrelated strains, using computer-assisted computation of similarity coefficients and the genesis of dendrograms, suggests that while Ct14 is more effective in grouping independent isolates, Ct3 is more effective in discriminating small differences in the patterns of highly related isolates and is therefore a more effective probe for determining microevolution within a clonal population and substrain shuffling in recurrent infections. Because of their alternative attributes, it is suggested that both probes be used in fingerprinting studies of C. tropicalis.

Cytoplasmic localization of the white phase-specific WH11 gene product of Candida albicans

Cells of Candida albicans WO-1 switch frequently, spontaneously and reversibly between a white and opaque phase. The white-opaque transition involves the regulation of phase-specific genes. In the white budding phase, cells express the white phase-specific gene WH11, which encodes a protein with homology to the heat shock protein Hsp12 of Saccharomyces cerevisiae. A recombinant Wh11 protein has been synthesized, purified to apparent homogeneity and used to generate a rabbit polyclonal antiserum. The antiserum was used to localize the Wh11 protein in white phase cells. Wh11 is distributed throughout the cytoplasm but appears to be excluded from vesicles, plasma membrane and nucleus. An analysis by Western blotting of Wh11 expression in a number of C. albicans strains and related species suggests a correlation between round budding cell shape and expression.

Temperature-dependent surface expression of the beta-2-integrin analogue of Candida albicans and its role in adhesion to the human endothelium

Candida albicans has become one of the most important pathogens in intensive care units. Adherence of C. albicans to the vascular endothelium is believed to represent a critical step in the pathogenesis of disseminated candidiasis and may involve molecules analogous to human beta 2-integrins such as the complement receptor 3 (CR3) analogue of C. albicans (C.a.-CR3). Its expression was detected by a sensitive rosetting assay when Candida was present in its hyphal form but not in its yeast form, the latter being generally considered to be less pathogenic. However, the presence of hyphae alone was not sufficient: C.a.-CR3 expression was found to be temperature-dependent for 4 (out of 10) clinical isolates. Two rosetted better after growth at 30 degrees C, the other 2 after growth at 37 degrees C. This temperature dependence was most pronounced for 1 laboratory strain: C.a.-CR3 expression was best at 30 degrees C and markedly decreased with increasing temperatures. At 37 degrees C no rosettes were detected at all. Modifications of the culture conditions (e.g. agitation, pH) exerted a marked influence on the morphology of this strain but always allowed rosette formation once hyphae were formed at 30 degrees C. However, none of these modifications was able to induce rosettes at 37 degrees C. Adhesion of C. albicans isolates to an endothelial cell line was also temperature-dependent but not strongly correlated with C.a.-CR3 expression. Most strains exhibited a better adherence when grown at 30 degrees C. This finding may be of importance for exogenous infections, with Candida spp. invading the body from the outside, where the temperature is usually lower than the physiological body temperature.

Gene regulation in the white–opaque transition ofCandida albicans

Most strains of Candida albicans switch frequently and reversibly among a number of different phenotypes distinguishable by colony morphology. Previous experiments indicated that switching involved differential gene expression. Using the white–opaque transition as a model switching system, we have cloned two opaque-specific genes, PEP1 and OP4, and one white specific gene, WH11. Differential transcription of these genes suggested that switching involves the coordinate regulation of batteries of unlinked phase-specific genes. It has been demonstrated that the frequency of integration at phase specific loci is a function of the transcriptional state of the phase-specific genes. In addition, a functional dissection of the 5′-upstream region of the WH11 gene has identified two major domains containing cis-acting regulatory sequences that are involved in phase-specific transcription. Gel retardation experiments provide evidence for white phase-specific trans-acting factors which form complexes with both domains. The regulation of the switching event is discussed. Key words: Candida albicans, phenotypic switching, white–opaque transition, phase-specific genes, integrative transformation, promoter regions, WH11 gene.

Colonizing populations of Candida albicans are clonal in origin but undergo microevolution through C1 fragment reorganization as demonstrated by DNA fingerprinting and C1 sequencing

The genetic homogeneity of nine commensal and infecting populations of Candida albicans has been assessed by fingerprinting multiple isolates from each population by Southern blot hybridization first with the Ca3 probe and then with the 0.98-kb C1 fragment of the Ca3 probe. The isolates from each population were highly related, demonstrating the clonal origin of each population, but each population contained minor variants, demonstrating microevolution. Variation in each case was limited to bands of the Ca3 fingerprint pattern which hybridized with the 0.98-kb C1 fragment. The C1 fragment was therefore sequenced and demonstrated to contain an RPS repetitive element. The C1 fragment also contained part or all of a true end of the RPS element. These results, therefore, demonstrate that most colonizing C. albicans populations in nonimmuno-suppressed patients are clonal, that microevolution can be detected in every colonizing population by C1 hybridization, and that C1 contains the repeat RPS element.

Stimulation of B-cell lymphopoiesis by interleukin-7 leads to aggravation of murine leishmaniasis

The effect of recombinant interleukin-7 (IL-7) on the clinical course of murine leishmaniasis and the development of the accompanying immune response was investigated. Previously, IL-7 has been shown to possess stimulatory capacity for different cell types of the immune and haematopoietic system critically involved in the defence against Leishmania major (L. major), such as macrophages which are activated for the elimination of the parasite by IL-7. In contrast to these in vitro data, the present study indicates that treatment of genetically susceptible BALB/c mice with IL-7 at the onset of the infection leads to enhanced lesion development and a significantly accelerated death of the animals. This was correlated with a 40-fold increased parasite burden in spleens and lymph nodes. While the specific antibody response against L. major was not altered and lymphocytes of IL-7-treated mice produced comparable amounts of the T-helper type-2 (Th2) cytokines IL-4 and IL-10, less interferon-gamma (IFN-gamma) was measurable after antigenic stimulation of lymph node and spleen cells in vitro. One of the major changes appearing by the first week after infection in IL-7-treated mice was the increase of the total cell number in spleen and lymph nodes draining the local infection. Analysis of the cellular composition revealed that the enhanced cellularity was predominantly due to a rise in the B-cell compartment. Since antigen presentation by B cells has been implicated in the development of Th2 cells, the disease-aggravating activity of IL-7 is thought to be primarily due to augmentation of B lymphopoiesis.

The frequency of integrative transformation at phase-specific genes of Candida albicans correlates with their transcriptional state

The phase transition between the white and opaque phenotypes in the switching system of Candida albicans strain WO-1 is accompanied by the differential expression of the white-specific gene WH11 and the opaque-specific gene PEP1. The frequency of integrative transformation at the white-specific gene locus WH11 is between 4.5 and 7.0 times more frequent in white than in opaque spheroplasts, and the frequency of disruptive transformation at the opaque-specific gene locus PEP1 is 30.5 times more frequent in opaque spheroplasts than in white spheroplasts. In contrast, the frequencies of integrative transformation at the constitutively expressed loci ADE2 and EF1 alpha 2 are similar in the white and opaque phases. Therefore, the frequency of integration of linear plasmid DNA containing sequences of phase-specific genes correlates with the transcriptional state of the targeted locus.

Evolution and replacement of Candida albicans strains during recurrent vaginitis demonstrated by DNA fingerprinting

Southern blot hybridization with the Ca3 probe and the C fragment of the Ca3 probe was used to assess the genetic relatedness of Candida albicans strains from one patient with recurrent C. albicans infection in whom the same strain was maintained, one patient in whom the infecting strain was replaced, and their male sexual partners. In the patient in whom the infecting strain was maintained, the infecting strain exhibited a minor genetic change in each successive episode of Candida vaginitis. These genetic changes occurred in the C-fragment bands of the Ca3 hybridization pattern. In the patient in whom the infecting strain was replaced by another infecting strain, a transition infection involved a genetically mixed infecting population, and the replacement strain appeared to have originated from the oral cavity of the male partner. The results demonstrate that the infecting strains of recurrent Candida vaginitis are not genetically stable, that drug treatment can result in the selection of variants of the previously infecting strain or replacement by a genetically unrelated strain, and that the male partner can be the source of a replacement strain.

Recombinant soluble interleukin-4 (IL-4) receptor acts as an antagonist of IL-4 in murine cutaneous Leishmaniasis

This study was performed to evaluate the soluble interleukin-4 receptor (sIL-4R) as a potential antagonist of interleukin-4 (IL-4) in an infectious disease. It is shown that antigen-triggered proliferation and cytokine secretion of Leishmania major-specific, cloned Th2 cells in vitro can be inhibited dose dependently by recombinant murine, but not control human, sIL-4R. In vivo, we found that endogenous synthesis of IL-4 mRNA is upregulated during the first week of infection, while an increase of IL-4R mRNA occurred later after infection of BALB/c mice with L. major. To interfere successfully with the IL-4 ligand-receptor interaction, we therefore chose to treat infected BALB/c mice with recombinant sIL-4R during the onset (e.g., days 0 to 7) of the immune response. Treatment with murine, but not with human, sIL-4R during the first week of infection rendered BALB/c mice clinically resistant to L. major, led to a 7- to 12-fold reduction of the parasite load in spleen and lymph nodes at 7 weeks of infection, shifted the pattern of cytokines towards a Th1 type, and provided durable resistance against reinfection. Thus, it could be demonstrated that the balance among sIL-4R, membrane-bound IL-4R, and their ligand IL-4 can be modulated in vivo, thereby modifying the antiparasitic immune response. These results suggest a therapeutic value of sIL-4R in diseases in which neutralization of IL-4 is desirable.

Interleukin-10 inhibits antimicrobial activity against Leishmania major in murine macrophages

The stimulation of macrophages is of importance to the defense against intracellularly replicating microorganisms such as Leishmania. In this study the direct effect of recombinant interleukin-10 (IL-10) on the leishmanicidal effector functions of murine peritoneal or bone marrow derived macrophages was investigated. IL-10 almost completely inhibited the killing of intracellular leishmania at concentrations above 10 ng/ml. This inhibitory effect was independent of the stimulus used as the activation of macrophages by IFN-gamma and IL-7, recently shown to possess macrophage activating properties, were suppressed by IL-10. Kinetic experiments revealed that IL-10 must be present during the process of macrophage activation and that the leishmanicidal effector function of fully activated macrophages was not influenced. Furthermore, in the absence of exogenously added IL-10, the addition of neutralizing antibodies against IL-10 or IL-10-specific antisense phosphorothioate DNA-oligonucleotide led to an enhanced killing of parasites after stimulation with either IFN-gamma or IL-7. In accordance with this, IL-10 mRNA was readily detectable in murine macrophages by PCR with reverse transcribed mRNA. These results indicate that IL-10, which is endogenously produced by macrophages, acts as an autocrine deactivating factor supporting the survival of the parasite.

Interleukin-7 enhances antimicrobial activity against Leishmania major in murine macrophages

Recently, it has been shown that interleukin-7 (IL-7) is able to induce secretion of cytokines and tumoricidal activity by human monocytes. This study shows that treatment of murine macrophages infected with Leishmania major with IL-7 without any other stimulus reduced the percentage of infected cells, as well as the parasite burden per cell, in a dose-dependent manner to a limited degree (45% reduction of the number of amastigotes per 100 macrophages). Simultaneous treatment of macrophages with gamma interferon and IL-7 led to nearly complete (> 99%) elimination of amastigotes. Addition of anti-tumor necrosis factor alpha or N omega-monomethyl-L-arginine acetate reversed the leishmanicidal effects of IL-7, and production of nitric oxide was induced in the presence of IL-7.

Immunization of susceptible hosts with a soluble antigen fraction from Leishmania major leads to aggravation of murine leishmaniasis mediated by CD4+ T cells

This study was performed in order to define Leishmania major antigens that function as disease-modulating immunogens in susceptible BALB/c mice. A soluble leishmanial antigen preparation (S-SLA) derived from highly infective stationary-phase L. major parasites was fractionated by preparative gel electrophoresis. In vitro, the low molecular mass fraction (less than 31 kDa) of S-SLA fraction D (FR D) was found to be a potent stimulator of L. major-specific Th1 and Th2 helper cell clones. In vivo, immunization with FR D induced a Th2-biased immune response in BALB/c mice as determined by the numbers of splenic CD4+ cells secreting interleukin 4 and interferon-gamma according to limiting dilution analyses. In addition, FR D caused significant disease exacerbation in parasite-infected susceptible mice as assessed by the local lesion development and the numbers of parasites in lymph nodes and spleen. This effect was observed after local subcutaneous application of FR D as well as after systemic immunization (intrasplenic or intraperitoneal). Transfer experiments revealed, that the disease-aggravating effect of FR D was mediated by CD4+ T cells. From these results it is concluded that leishmanial protein preparations exist that not only fail to induce protective anitparasitic immunity, but can mediate disease exacerbation, independently of the primary application site of the immunogen. The existence of such structures may serve the parasite as a means to evade the host's immune attack and may also have implications for the development of vaccines.