Sterol and fatty acid composition of Candida lusitaniae clinical isolates

Candida lusitaniae: Biology, Pathogenicity, Virulence Factors, Diagnosis, and Treatment

The incidence of fungal infections is increasing at an alarming rate and has posed a great challenge for science in recent years. The rise in these infections has been related to the increase in immunocompromised patients and the resistance of different species to antifungal drugs. Infections caused by the different Candida species, especially Candida albicans, are one of the most common mycoses in humans, and the etiological agents are considered opportunistic pathogens associated with high mortality rates when disseminated infections occur. Candida lusitaniae is considered an emerging opportunistic pathogen that most frequently affects immunocompromised patients with some comorbidity. Although it is a low-frequency pathogen, and the mortality rate of C. lusitaniae-caused candidemia does not exceed 5%, some isolates are known to be resistant to antifungals such as amphotericin B, 5-fluorocytosine, and fluconazole. In this paper, a detailed review of the current literature on this organism and its different aspects, such as its biology, possible virulence factors, pathogen-host interaction, diagnosis, and treatment of infection, is provided. Of particular interest, through Blastp analysis we predicted possible virulence factors in this species.

The Role of Signaling via Aqueous Pore Formation in Resistance Responses to Amphotericin B

Drug resistance studies have played an important role in the validation of antibiotic targets. In the case of the polyene antibiotic amphotericin B (AmB), such studies have demonstrated the essential role that depletion of ergosterol plays in the development of AmB-resistant (AmB-R) organisms. However, AmB-R strains also occur in fungi and parasitic protozoa that maintain a normal level of ergosterol at the plasma membrane. Here, I review evidence that shows not only that there is increased protection against the deleterious consequences of AmB-induced ion leakage across the membrane in these resistant pathogens but also that a set of events are activated that block the cell signaling responses that trigger the oxidative damage produced by the antibiotic. Such signaling events appear to be the consequence of a membrane-thinning effect that is exerted upon lipid-anchored Ras proteins by the aqueous pores formed by AmB. A similar membrane disturbance effect may also explain the activity of AmB on mammalian cells containing Toll-like receptors. These resistance mechanisms expand our current understanding of the role that the formation of AmB aqueous pores plays in triggering signal transduction responses in both pathogens and host immune cells.

Fatty acid profile and influence of oxythiamine on fatty acid content in Malassezia pachydermatis, Candida albicans and Saccharomyces cerevisiae

Malassezia pachydermatis and Candida albicans are fungi involved in the skin diseases and systemic infections. The therapy of such infections is difficult due to relapses and problems with pathogen identification. In our study, we compare the fatty acids profile of M. pachydermatis, C. albicans and S. cerevisiae to identify diagnostic markers and to investigate the effect of oxythiamine (OT) on the lipid composition of these species. Total fatty acid content is threefold higher in C. albicans and M. pachydermatis compared with S. cerevisiae. These two species have also increased level of polyunsaturated fatty acids (PUFA) and decreased content of monounsaturated fatty acids (MUFA). We noted differences in the content of longer chain (>18) fatty acids between studied species (for example a lack of 20 : 1 in S. cerevisiae and 22 : 0 in M. pachydermatis and C. albicans). OT reduces total fatty acids content in M. pachydermatis by 50%. In S. cerevisiae, OT increased PUFA whereas it decreased MUFA content. In C. albicans, OT decreased PUFA and increased MUFA and SFA content. The results show that the MUFA to PUFA ratio and the fatty acid profile could be useful diagnostic tests to distinguish C. albicans, M. pachydermatis and S. cerevisiae, and OT affected the lipid metabolism of the investigated species, especially M. pachydermatis.

Steroidal Glycosides from the Seeds of Hyoscyamus Niger L. and their Antifungal Activity

Phytochemical analysis of the seeds of Hyocyamus niger L. (Solonaceae) resulted in the isolation of six steroidal glycosides, two furostanol (1, 2) and four spirostanol saponins (3, 4, 5, 6), which were found in this plant for the first time. The structures of these compounds were determined by detailed analysis of their spectral data, including two-dimensional NMR spectroscopy and MS spectroscopy. The antifungal activity of a crude steroidal glycoside extract, fractions of spirostanoles and individual glicosides was investigated in vitro against a panel of human pathogenic fungi, yeasts as well as dermatophytes and filamentous species.

Phenotypic switching in Candida lusitaniae on copper sulfate indicator agar: association with amphotericin B resistance and filamentation

Candida lusitaniae is an opportunistic yeast pathogen that has the ability to develop resistance to amphotericin B (AmB). The mechanism(s) for this resistance is not well understood, although there are data supporting mutations in sterol pathways and other data supporting phenotypic switching (PS). The goal of this study was to determine whether C. lusitaniae has a PS system and to characterize any phenotypes, including any changes in AmB MICs. When 10(4) CFU of an AmB-resistant (MIC of 16 to 32 microg/ml) clinical strain was plated on yeast-peptone-dextrose (YPD) agar with 1 mM CuSO(4), three colony colors were observed: light brown (LB) >> dark brown (DB) > white (W), similar to the result for Candida glabrata. Switching did occur with high AmB resistance (MIC of 256 microg/ml) being associated with W, whereas LB and DB colonies had MICs of 2 to 8 microg/ml and 2 to 16 microg/ml, respectively. Filamentation (pseudohyphae) was associated with DB colonies. All phenotypes occurred spontaneously with greater frequency ( approximately 10(-2) to 10(-4)) than spontaneous mutations, and all phenotypes were reversible, fulfilling the two PS criteria. High AmB MICs were always associated with W colonies but not with all W colonies. Detection of PS on YPD-CuSO(4) is also similar to that in Candida glabrata, and we hypothesize that this is due to similarities in metallothionein gene expression. Phenotypic switching represents a key strategy in C. lusitaniae that confers a selective advantage during environmental challenges, including the ability to switch to AmB resistance.

Antifungal activity of steroidal glycosides fromYucca gloriosa L

The antifungal activity of a crude steroidal glycoside extract from Yucca gloriosa flowers, named alexin, was investigated in vitro against a panel of human pathogenic fungi, yeasts as well as dermatophytes and filamentous species. The minimal inhibitory concentration (MIC) was determined by an agar dilution method. Alexin had a broad spectrum of antifungal activity, found to reside entirely in the spirostanoid fraction. The major tigogenyl glycosides, yuccaloeside B and yuccaloeside C, exhibited MICs between 0.39 and 6.25 microg[sol ]mL for all the tested yeast strains except for two (C. lusitaniae and C. kefyr). They were also active against several clinical Candida isolates known to be resistant to the usual antifungal agents. The MICs for the dermatophytes were between 0.78 and 12.5 microg[sol ]mL. The most sensitive filamentous species was A. fumigatus (MIC = 1.56 microg[sol ]mL). For most of the strains, the MICs of both glycosides were similar to those of the reference antifungal agent.

Emerging fungal resistance

There has been an increase in systemic fungal infections over the past several decades, partially because of an increasing number of critically ill patients, surgical procedures, and immunosuppressive therapies, as well as the use of more invasive diagnostic and therapeutic medical procedures. Concomitant with this increase in infections has been the increase in azole-resistant Candida species and opportunistic molds with intrinsic resistance to many of the currently available antifungal agents. This review focuses on antifungal resistance, with emphasis on emerging resistance patterns and emerging fungi that are intrinsically resistant to antifungal agents.

Disruption of ergosterol biosynthesis, growth, and the morphological transition inCandida albicansby sterol methyltransferase inhibitors containing sulfur at C-25 in the sterol side chain

The sterol substrate analog 25-thialanosterol and its corresponding sulfonium salt were evaluated for their ability to serve as antifungal agents and to inhibit sterol methyltransferase (SMT) activity in Candida albicans. Both compounds inhibited cell proliferation, were fungistatic, interrupted the yeast-like-form to germ-tube-form transition, and resulted in the accumulation of zymosterol and related delta24-sterols concurrent with a decrease in ergosterol, as was expected for the specific inhibition of SMT activity. Feedback on sterol synthesis was evidenced by elevated levels of cellular sterols in treated vs. control cultures. However, neither farnesol nor squalene accumulated in significant amounts in treated cultures, suggesting that carbon flux is channeled from the isoprenoid pathway to the sterol pathway with minor interruption or redirection until blockage at the C-methylation step. Activity assays using solubilized C. albicans SMT confirmed the inhibitors impair SMT action. Kinetic analysis indicated that 25-thialanosterol inhibited SMT with the properties of a time-dependent mechanism-based inactivator Ki of 5 microM and apparent kinact of 0.013 min(-1), whereas the corresponding sulfonium salt was a reversible-type transition state analog exhibiting a Ki of 20 nM. The results are interpreted to imply changes in ergosterol homeostasis as influenced by SMT activity can control growth and the morphological transition in C. albicans, possibly affecting disease development.

Colony morphology switching of Candida lusitaniae and acquisition of multidrug resistance during treatment of a renal infection in a newborn: case report and review of the literature

Candida lusitaniae is an emerging opportunistic pathogen which exhibits an unusual antifungal susceptibility pattern. We describe a case of fatal renal infection due to C. lusitaniae in a very low birth weight neonate who was treated with short courses of fluconazole given alternately with amphotericin B. A colony morphology switching was detected on the standard primary culture medium by changes in colony size. Switching was shown to affect deeply the susceptibility to amphotericin B. Afterwards, the switched phenotype developed a cross resistance to fluconazole and itraconazole. Several issues raised by this case are discussed in the light of an extensive review of the literature. Our observations point out the importance of both the detection of colony morphology switching and the close monitoring of antifungal susceptibility in the management of infections due to C. lusitaniae. A judicious therapeutic strategy should prevent the acquisition of multidrug resistance during antifungal therapy.

Disruption of ergosterol biosynthesis confers resistance to amphotericin B in Candida lusitaniae

Candida lusitaniae is an emerging human pathogen that, unlike other fungal pathogens, frequently develops resistance to the commonly used antifungal agent amphotericin B. Amphotericin B is a member of the polyene class of antifungal drugs, which impair fungal cell membrane integrity. Here we analyzed mechanisms contributing to amphotericin B resistance in C. lusitaniae. Sensitivity to polyenes in the related fungi Saccharomyces cerevisiae and Candida albicans requires the ergosterol biosynthetic gene ERG6. In an effort to understand the mechanisms contributing to amphotericin B resistance in C. lusitaniae, we isolated the ERG6 gene and created a C. lusitaniae erg6 delta strain. This mutant strain exhibited a growth defect, was resistant to amphotericin B, and was hypersensitive to other sterol inhibitors. Based on the similarities between the phenotypes of the erg6 delta mutant and clinical isolates of C. lusitaniae resistant to amphotericin B, we analyzed ERG6 expression levels and ergosterol content in multiple clinical isolates. C. lusitaniae amphotericin B-resistant isolates were found to have increased levels of ERG6 transcript as well as reduced ergosterol content. These changes suggest that another gene in the ergosterol biosynthetic pathway could be mutated or misregulated. Further transcript analysis showed that expression of the ERG3 gene, which encodes C-5 sterol desaturase, was reduced in two amphotericin B-resistant isolates. Our findings reveal that mutation or altered expression of ergosterol biosynthetic genes can result in resistance to amphotericin B in C. lusitaniae.