Fungal colonization of haematological patients receiving cytotoxic chemotherapy: emergence of azole-resistant Saccharomyces cerevisiae

Bloodstream infection by Saccharomyces cerevisiae in a COVID-19 patient receiving probiotic supplementation in the ICU in Brazil

Care-related infections (CRIs) have a negative impact on the morbidity and mortality of patients in intensive care. Among them, fungal infections (e.g. Candida spp. and Aspergillus spp.) have high mortality in critically ill patients, particularly those with acute respiratory distress syndrome (ARDS) and immunosuppression. Coronavirus disease 2019 (COVID-19) causes severe respiratory changes and deregulation of the immune system. Here, we describe a case of fungal infection in an intensive care unit (ICU) patient with COVID-19 caused by Saccharomyces cerevisiae, a yeast widely used in the baking and wine production industries. It is also used as a probiotic, both for prevention and as adjunctive therapy in patients with diarrhoea. The patient was admitted to the ICU with a diagnosis of COVID-19, respiratory failure, complications of ARDS and renal failure, and was being treated with antibiotics and vasoactive amines. Later, the patient had diarrhoea and, after supplementation with Saccharomyces, he developed a bloodstream infection with Saccharomyces. The patient died after 61 days of hospitalization due to thrombocytopenia and bleeding. This case report suggests avoiding the use of probiotics in intensive care patients under the administration of antibiotics and amines, and with damage to the intestinal mucosa and immunodeficiency caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), since these factors could favour the translocation of fungi.

Recent developments in less known and multi-resistant fungal opportunists

Fungal infections have increased in recent years due to host factors, such as oncohaematological and transplant-related disorders, immunosuppressive therapy, and AIDS. Additionally, molecular and proteomic facilities have become available to identify previously unrecognizable opportunists. For these reasons, reports on less-known and recalcitrant mycoses, such as those caused by black fungi, hyaline filamentous fungi, coelomycetes, Mucorales, and non-Candida yeasts have emerged. In this review, novel taxonomy in these groups, which often are multi-resistant to one or several classes of antifungals, is discussed. Clinical presentations, diagnosis and current treatment of some major groups are summarised.

N-alkylated linear heptamethine polyenes as potent non-azole leads against Candida albicans fungal infections

In this study, eighteen heptamethine dyes were synthesised and their antifungal activities were evaluated against three clinically relevant yeast species.. The eighteen dyes were placed within classes based on their core subunit i.e. 2,3,3-trimethylindolenine (5a-f), 1,1,2-trimethyl-1H-benzo[e]indole (6a-f), or 2-methylbenzothiazole (7a-f). The results presented herein imply that the three families of cyanine dyes, in particular compounds 5a-f, show high potential as selective scaffolds to treat C. albicans infections. This opens up the opportunity for further optimisation and investigation of this class compounds for potential antifungal treatment.

Bloodstream Infection by Saccharomyces cerevisiae in Two COVID-19 Patients after Receiving Supplementation of Saccharomyces in the ICU

Co-infections have an unknown impact on the morbidity and mortality of the new clinical syndrome called coronavirus disease 2019 (COVID-19). The syndrome is caused by the new pandemic coronavirus SARS-CoV-2 and it is probably connected with severe traces in the elements of the immune system. Apart from possible Aspergillus infections, particularly in patients with acute respiratory distress syndrome (ARDS), other fungal infections could occur, probably more easily, due to the immunological dysregulation and the critical condition of these patients. Probiotic preparations of Saccharomyces are broadly used for the prevention of antibiotic-associated complications, especially in the intensive care units (ICU). On the other hand, Saccharomyces organisms are reported as agents of invasive infection in immunocompromised or critically ill patients. We report two cases of bloodstream infection by Saccharomyces in two patients hospitalised in the ICU, due to severe COVID-19, after Saccharomyces supplementation.

Recurrent fungal endophthalmitis after intravitreal injections of bevacizumab

Purpose

We intend to describe an uncommon case of recurrent post-cataract fungal endophthalmitis after intravitreal injections of Bevacizumab.

Observations

A 73-year-old male, who underwent an uncomplicated cataract surgery 8 months ago, presented to our department with postoperative endophthalmitis 5 days after his fifth intravitreal injection (IVI) of bevacizumab for treatment of cystoid macula edema caused by central retinal venous occlusion 6 months ago. The visual acuity (VA) was 0.1 (20/200). The patient underwent an emergency pars plana vitrectomy. Culture of vitreous tap was negative. Eight weeks later, the patient presented again with recurrent endophthalmitis 2 days after his sixth IVI of bevacizumab. VA was hand motion. The patient was treated with an emergency anterior and posterior segment washout with intracapsular posterior intraocular lens (pIOL) extraction. Culture of pIOL revealed Saccharomyces cervisiae fungi in the capsular bag. Six months later, clinical findings were stable with no signs of intraocular inflammation, VA was 0.3 (20/60).

Conclusions and Importance

we assume that this is a rare case of chronic late-onset post-cataract fungal endophthalmitis, which was activated by repeated intravitreal injections of Bevacizumab.

Experience with Saccharomyces boulardii Probiotic in Oncohaematological Patients

Very few reports have been published to date on the bloodstream infections caused by Saccharomyces spp. in oncohaematological patients, and there are no guidelines on the use of this probiotic microorganism in this population. We describe the use of probiotic preparation containing Saccharomyces boulardii in a large group of oncohaematological patients. We retrospectively analysed the data from 32,000 patient hospitalisations at the haematological centre during 2011–2013 (including 196 haematopoietic stem cell transplant recipients) in a tertiary care university-affiliated hospital. During the study period, 2270 doses of Saccharomyces boulardii probiotic were administered to the oncohaematological patients. In total, 2816 mycological cultures were performed, out of which 772 (27.4%) were positive, with 52 indicating digestive tract colonisation by Saccharomyces spp., mainly in patients with acute myeloid leukaemia (AML), myelodysplastic syndrome (MDS) or multiple myeloma (MM). While colonised, they were hospitalised for 1683 days and 416 microbiological cultures of their clinical samples were performed. In the studied group of patients, there were six blood cultures positive for fungi; however, they comprised Candida species: two C. glabrata, one C. albicans, one C. krusei, one C. tropicalis and one C. parapsilosis. There was no blood culture positive for Saccharomyces spp. Our study indicates that despite colonisation of many oncohaematological patients with Saccharomyces spp., there were no cases of fungal sepsis caused by this species.

Biodiversity of the human oral mycobiome in health and disease

The organisms that colonize the human body over a lifetime are diverse, extensive and gargantuan. A fair proportion of the microbiota that constitutes this human microbiome live within our oral cavities mostly as harmonious associates causing only sporadic disease. An important core constituent of the microbiome is the mycobiome, representing various fungal genera. Up until recently, only a few species of fungi, mainly Candida species, were thought to constitute the human oral mycobiome. The reasons for this are manifold, although the uncultivable nature of many fungi in conventional laboratory media, and their complex genetic composition seem to be the major factors which eluded their detection over the years. Nevertheless, recent advances in computing and high-throughput sequencing such as next-generation sequencing (NGS) platforms have provided us a panoramic view of a totally new world of fungi that are human oral cohabitués. Their diversity is perplexing, and functionality yet to be deciphered. Here, we provide a glimpse of what is currently known of the oral mycobiome, in health and disease, with some future perspectives.

Rare fungal infectious agents: a lurking enemy

In the expanding population of immunocompromised patients and those treated in intensive care units, rare fungal infectious agents have emerged as important pathogens, causing invasive infections associated with high morbidity and mortality. These infections may present either as de novo or as breakthrough invasive infections in high-risk patients with hematologic malignancies receiving prophylactic or empirical antifungal therapy or in patients with central venous catheters. Diagnosis and treatment are challenging. Physicians should have a high index of suspicion because early diagnosis is of paramount importance. Conventional diagnostic methods such as cultures and histopathology are still essential, but rapid and more specific molecular techniques for both detection and identification of the infecting pathogens are being developed and hopefully will lead to early targeted treatment. The management of invasive fungal infections is multimodal. Reversal of risk factors, if feasible, should be attempted. Surgical debridement is recommended in localized mold infections. The efficacy of various antifungal drugs is not uniform. Amphotericin B is active against most yeasts, except Trichosporon, as well as against Mucorales, Fusarium, and some species of Paecilomyces and dimorphic fungi. The use of voriconazole is suggested for the treatment of trichosporonosis and scedosporiosis. Combination treatment, though recommended as salvage therapy in some infections, is controversial in most cases. Despite the use of available antifungals, mortality remains high. The optimization of molecular-based techniques, with expansion of reference libraries and the possibility for direct detection of resistance mechanisms, is awaited with great interest in the near future. Further research is necessary, however, in order to find the best ways to confront and destroy these lurking enemies.

Multiple Approaches Detect the Presence of Fungi in Human Breastmilk Samples from Healthy Mothers

Human breastmilk contains a variety of bacteria that are transmitted to the infant and have been suggested to contribute to gut microbiota development and immune maturation. However, the characterization of fungal organisms in milk from healthy mothers is currently unknown although their presence has been reported in the infant gut and also in milk from other mammals. Breastmilk samples from healthy lactating mothers (n = 65) within 1 month after birth were analyzed. Fungal presence was assessed by different techniques, including microscopy, growth and identification of cultured isolates, fungal load estimation by qPCR, and fungal composition using 28S rRNA gene high-throughput sequencing. In addition, milk macronutrients and human somatic cells were quantified by spectrophotometry and cytometry. qPCR data showed that 89% of samples had detectable levels of fungal DNA, at an estimated median load of 3,5 × 10⁵ cells/ml, potentially including both viable and non-viable fungi. Using different culture media, 33 strains were isolated and identified, confirming the presence of viable fungal species. Pyrosequencing results showed that the most common genera were Malassezia (44%), followed by Candida (19%) and Saccharomyces (12%). Yeast cells were observed by fluorescence microscopy. Future work should study the origin of these fungi and their potential contribution to infant health.

SACCHAROMYCES CEREVISIAE FUNGEMIA IN A PEDIATRIC PATIENT AFTER TREATMENT WITH PROBIOTICS

Objective:

To report the case of a one-year-old patient with a bloodstream infection associated with probiotics, and to discuss the indications and precautions concerning the therapeutic use of probiotics.

Case description:

A one-year-old male patient with Down syndrome in a late postoperative period of congenital cardiac disease correction. The patient was severely malnourished and had been hospitalized since he was two months old in the Pediatric Intensive Care Unit. While in the hospital, the patient presented multiple infections related to mechanical ventilation and invasive devices, and received recurrent treatment with broadspectrum antibiotics for long periods. The patient developed chronic diarrhea and feeding intolerance, which lead to the use of probiotics (Saccharomyces boulardii) for four days. Two days after the end of the treatment, the patient developed septic shock, and the Saccharomyces cerevisiae was isolated in the central and peripheral blood cultures. After antifungal treatment (Amphotericin B), the blood cultures were negative. The patient had no further clinical complications after this event.

Comments:

Despite the well-documented benefits of probiotics in some clinical situations, we should be cautious about the indication of their use, preparation, and administration, in addition to the safe handling of invasive devices.

Yeasts

Yeasts are unicellular organisms that reproduce mostly by budding and less often by fission. Most medically important yeasts originate from Ascomycota or Basidiomycota. Here, we review taxonomy, epidemiology, disease spectrum, antifungal drug susceptibility patterns of medically important yeast, laboratory diagnosis, and diagnostic strategies.

Fatal course of Saprochaete capitata fungemia in children with acute lymphoblastic leukemia

Saprochaete capitata (S. capitata) is a very rare fungal pathogen that causes disseminated opportunistic infections in patients with hematologic malignancies. Fever resistant to broad-spectrum antibiotic and antifungal treatment is common in the presence of fungemia during the period of profound neutropenia. We describe three cases of leukemic children who died from S. capitata fungemia following a first febrile neutropenic episode after the induction of chemotherapy. S. capitata fungemia is an emergent infection associated with high mortality and low susceptibility to fluconazole and echinocandins. Awareness of this emergent infection is needed to ensure that it can be properly treated.

Seven cases of Saccharomyces fungaemia related to use of probiotics

Probiotics are increasingly used in critically ill patients without enough safety data. The aim of the present study was to determine the association of probiotics with Saccharomyces cerevisiae fungaemia. Seven patients with S. cerevisiae fungaemia were reported at two hospitals in India between July 2014 and September 2015. Detailed clinical history of patients was recorded. Besides the seven patient isolates, three probiotics sachets used in those patients and five unrelated clinical isolates were used for association study by Fluorescent amplified fragment length polymorphism (FAFLP). Antifungal susceptibility testing was performed by broth microdilution technique of CLSI (M27-A3) and interpreted according to CLSI (M27S4). Two patients were premature neonates and five were adults. They were admitted in intensive care unit and were on probiotics containing S. boulardii (except one adult patient). FAFLP analysis showed 96.4-99.7% similarity between blood and corresponding probiotic isolates. Of the three AFLP types (group I, II, II) identified, all the probiotic isolates clustered in group I (major cluster) including majority of the blood isolates. The isolates were susceptible to all antifungal agents tested. Five patients, who could be evaluated, responded promptly to echinocandins or voriconazole. As the prescription of probiotic containing S. boulardii in critically ill patient's leads to the fungaemia, we recommend avoiding this probiotic in those patients.

Whole Genome Analysis of 132 Clinical Saccharomyces cerevisiae Strains Reveals Extensive Ploidy Variation

Budding yeast has undergone several independent transitions from commercial to clinical lifestyles. The frequency of such transitions suggests that clinical yeast strains are derived from environmentally available yeast populations, including commercial sources. However, despite their important role in adaptive evolution, the prevalence of polyploidy and aneuploidy has not been extensively analyzed in clinical strains. In this study, we have looked for patterns governing the transition to clinical invasion in the largest screen of clinical yeast isolates to date. In particular, we have focused on the hypothesis that ploidy changes have influenced adaptive processes. We sequenced 144 yeast strains, 132 of which are clinical isolates. We found pervasive large-scale genomic variation in both overall ploidy (34% of strains identified as 3n/4n) and individual chromosomal copy numbers (36% of strains identified as aneuploid). We also found evidence for the highly dynamic nature of yeast genomes, with 35 strains showing partial chromosomal copy number changes and eight strains showing multiple independent chromosomal events. Intriguingly, a lineage identified to be baker's/commercial derived with a unique damaging mutation in NDC80 was particularly prone to polyploidy, with 83% of its members being triploid or tetraploid. Polyploidy was in turn associated with a >2× increase in aneuploidy rates as compared to other lineages. This dataset provides a rich source of information on the genomics of clinical yeast strains and highlights the potential importance of large-scale genomic copy variation in yeast adaptation.

Invasive Saccharomyces cerevisiae in a liver transplant patient: case report and review of infection in transplant recipients

Saccharomyces cerevisiae, an ascosporogenous yeast commonly used in the production of food, is an emerging infection in immunocompromised patients. We report the case of a 60-year-old man whose orthotopic liver transplant was complicated by S. cerevisiae fungemia and peritoneal abscess, successfully treated with caspofungin and drainage. We also review the literature of invasive saccharomycoses in recipients of hematologic and solid organ transplants.

The 100-genomes strains, an S. cerevisiae resource that illuminates its natural phenotypic and genotypic variation and emergence as an opportunistic pathogen

Saccharomyces cerevisiae, a well-established model for species as diverse as humans and pathogenic fungi, is more recently a model for population and quantitative genetics. S. cerevisiae is found in multiple environments—one of which is the human body—as an opportunistic pathogen. To aid in the understanding of the S. cerevisiae population and quantitative genetics, as well as its emergence as an opportunistic pathogen, we sequenced, de novo assembled, and extensively manually edited and annotated the genomes of 93 S. cerevisiae strains from multiple geographic and environmental origins, including many clinical origin strains. These 93 S. cerevisiae strains, the genomes of which are near-reference quality, together with seven previously sequenced strains, constitute a novel genetic resource, the “100-genomes” strains. Our sequencing coverage, high-quality assemblies, and annotation provide unprecedented opportunities for detailed interrogation of complex genomic loci, examples of which we demonstrate. We found most phenotypic variation to be quantitative and identified population, genotype, and phenotype associations. Importantly, we identified clinical origin associations. For example, we found that an introgressed PDR5 was present exclusively in clinical origin mosaic group strains; that the mosaic group was significantly enriched for clinical origin strains; and that clinical origin strains were much more copper resistant, suggesting that copper resistance contributes to fitness in the human host. The 100-genomes strains are a novel, multipurpose resource to advance the study of S. cerevisiae population genetics, quantitative genetics, and the emergence of an opportunistic pathogen.

The human mycobiome

Fungi are fundamental to the human microbiome, the collection of microbes distributed across and within the body, and the microbiome has been shown, in total, to modify fundamental human physiology, including energy acquisition, vitamin-cofactor availability, xenobiotic metabolism, immune development and function, and even neurological development and behavior. Here, a comprehensive review of current knowledge about the mycobiome, the collective of fungi within the microbiome, highlights methods for its study, diversity between body sites, and dynamics during human development, health, and disease. Early-stage studies show interactions between the mycobiome and other microbes, with host physiology, and in pathogenic and mutualistic phenotypes. Current research portends a vital role for the mycobiome in human health and disease.

Epidemiology of Candida kefyr in patients with hematologic malignancies

Candida kefyr is an emerging pathogen among patients with hematologic malignancies (HM). We performed a retrospective study at Johns Hopkins Hospital to evaluate the epidemiology of C. kefyr colonization and infection in HM patients between 2004 and 2010. Eighty-three patients were colonized and/or infected with C. kefyr, with 8 (9.6%) having invasive candidiasis (IC). The yearly incidence of C. kefyr colonization and candidemia increased over the study period (P < 0.01), particularly after 2009. In 2010, C. kefyr caused 16.7% of candidemia episodes. The monthly incidence of C. kefyr was higher during the summer throughout the study. In a cohort of patients with acute myelogenic leukemia receiving induction chemotherapy, risks for C. kefyr colonization included the summer season (odds ratio [OR], 3.1; P = 0.03); administration of an azole (OR, 0.06; P < 0.001) or amphotericin B (OR, 0.35; P = 0.05) was protective. Fingerprinting of 16 isolates by repetitive sequence-based PCR showed that all were different genotypes. The epidemiology of C. kefyr candidemia was evaluated in another hospital in Montreal, Canada; data confirmed higher rates of C. kefyr infection in the summer. C. kefyr appears to be increasing in HM patients, with prominent summer seasonality. These findings raise questions about the effect of antifungal agents and health care exposures (e.g., yogurt) on the epidemiology of this yeast.

[Saccharomyces cerevisiae infections]

BACKGROUND

Saccharomyces cerevisiae is an ubiquitous yeast widely used in industry and it is also a common colonizer of the human mucosae. However, the incidence of invasive infection by these fungi has significantly increased in the last decades.

AIMS

To evaluate the infection by S. cerevisiae in a hospital in southern Brazil during a period of 10 years (2000-2010).

METHODS

Review of medical records of patients infected by this fungus.

RESULTS

In this period, 6 patients were found to be infected by S. cerevisiae. The age range of the patients was from 10 years to 84. Urine, blood, ascitic fluid, peritoneal dialysis fluid, and esophageal biopsy samples were analyzed. The predisposing factors were cancer, transplant, surgical procedures, renal failure, use of venous catheters, mechanical ventilation, hospitalization in Intensive Care Unit, diabetes mellitus, chemotherapy, corticosteroid use, and parenteral nutrition. Amphotericin B and fluconazole were the treatments of choice. Three of the patients died and the other 3 were discharged from hospital.

CONCLUSIONS

We must take special precautions in emerging infections, especially when there are predisposing conditions such as immunosuppression or patients with serious illnesses. The rapid and specific diagnosis of S. cerevisiae infections is important for therapeutic decision. Furthermore, epidemiological and efficacy studies of antifungal agents are necessary for a better therapeutic approach.

Role of probiotics in prevention of Candida infection in critically ill children

Candidiasis accounts for 10-20% of bloodstream infections in paediatric intensive care units (PICUs) and a significant increase in morbidity, mortality, and length of hospital stay. Enteric colonisation by Candida species is one of the most important risk factor for invasive candidiasis. The local defence mechanisms may be altered in critically ill patients, thus facilitating Candida overgrowth and candidiasis. Systemic antifungals have been proven to be effective in reducing fungal colonisation and invasive fungal infections, but their use is not without harms. Early restoration or maintenance of intestinal microbial flora using probiotics could be one of the important tools for reducing Candida infection. A few studies have demonstrated that probiotics are able to prevent Candida growth and colonisation in neonates, whereas their role in preventing invasive candidiasis in such patients is still unclear. Moreover, there are no published data on role of probiotics supplementation in the prevention of candidiasis in critically ill children beyond neonatal period. There are gap in our knowledge regarding efficacy, cost effectiveness, risk-benefit potential, optimum dose, frequency and duration of treatment of probiotics in prevention of fungal infections in critically ill children. Studies exploring and evaluating the role of probiotics in prevention of Candida infection in critically ill children are needed.

Genome-wide association analysis of clinical vs. nonclinical origin provides insights into Saccharomyces cerevisiae pathogenesis

Because domesticated Saccharomyces cerevisiae strains have been used to produce fermented food and beverages for centuries without apparent health implications, S. cerevisiae has always been considered a Generally Recognized As Safe (GRAS) microorganism. However, the number of reported mucosal and systemic S. cerevisiae infections in the human population has increased and fatal infections have occurred even in relatively healthy individuals. In order to gain insight into the pathogenesis of S. cerevisiae and improve our understanding of the emergence of fungal pathogens, we performed a population-based genome-wide environmental association analysis of clinical vs. nonclinical origin in S. cerevisiae. Using tiling array-based, high-density genotypes of 44 clinical and 44 nonclinical S. cerevisiae strains from diverse geographical origins and source substrates, we identified several genetic loci associated with clinical background in S. cerevisiae. Associated polymorphisms within the coding sequences of VRP1, KIC1, SBE22 and PDR5, and the 5' upstream region of YGR146C indicate the importance of pseudohyphal formation, robust cell wall maintenance and cellular detoxification for S. cerevisiae pathogenesis, and constitute good candidates for follow-up verification of virulence and virulence-related factors underlying the pathogenicity of S. cerevisiae.

Epidemiology of invasive mycoses in North America

The incidence of invasive mycoses is increasing, especially among patients who are immunocompromised or hospitalized with serious underlying diseases. Such infections may be broken into two broad categories: opportunistic and endemic. The most important agents of the opportunistic mycoses are Candida spp., Cryptococcus neoformans, Pneumocystis jirovecii, and Aspergillus spp. (although the list of potential pathogens is ever expanding); while the most commonly encountered endemic mycoses are due to Histoplasma capsulatum, Coccidioides immitis/posadasii, and Blastomyces dermatitidis. This review discusses the epidemiologic profiles of these invasive mycoses in North America, as well as risk factors for infection, and the pathogens' antifungal susceptibility.

Characterization of the oral fungal microbiome (mycobiome) in healthy individuals

The oral microbiome–organisms residing in the oral cavity and their collective genome–are critical components of health and disease. The fungal component of the oral microbiota has not been characterized. In this study, we used a novel multitag pyrosequencing approach to characterize fungi present in the oral cavity of 20 healthy individuals, using the pan-fungal internal transcribed spacer (ITS) primers. Our results revealed the “basal” oral mycobiome profile of the enrolled individuals, and showed that across all the samples studied, the oral cavity contained 74 culturable and 11 non-culturable fungal genera. Among these genera, 39 were present in only one person, 16 genera were present in two participants, and 5 genera were present in three people, while 15 genera (including non-culturable organisms) were present in ≥4 (20%) participants. Candida species were the most frequent (isolated from 75% of participants), followed by Cladosporium (65%), Aureobasidium, Saccharomycetales (50% for both), Aspergillus (35%), Fusarium (30%), and Cryptococcus (20%). Four of these predominant genera are known to be pathogenic in humans. The low-abundance genera may represent environmental fungi present in the oral cavity and could simply be spores inhaled from the air or material ingested with food. Among the culturable genera, 61 were represented by one species each, while 13 genera comprised between 2 and 6 different species; the total number of species identified were 101. The number of species in the oral cavity of each individual ranged between 9 and 23. Principal component (PCO) analysis of the obtained data set followed by sample clustering and UniFrac analysis revealed that White males and Asian males clustered differently from each other, whereas both Asian and White females clustered together. This is the first study that identified the “basal mycobiome” of healthy individuals, and provides the basis for a detailed characterization of the oral mycobiome in health and disease.

We characterized the fungal microbiome (mycobiome) of the oral cavity in healthy individuals. Our results demonstrate that the fungal component of the oral microbiome is diverse as revealed by the presence of 74 culturable and 11 non-culturable fungal genera in the oral cavity. A total of 101 species were identified, with between 9 and 23 culturable species present in each person. Fifteen genera (which included four known pathogenic fungi and non-culturable organisms) were present in ≥20% of the tested samples; Candida species were the most frequently obtained genera, isolated from 75% of all study participants, followed by Cladosporium (65%), Aureobasidium, Saccharomycetales (50% for both), Aspergillus (35%), Fusarium (30%), and Cryptococcus (20%). The remaining fungi detected in the oral wash samples represent organisms likely originating from the environment. This is the first study that identified the “basal mycobiome” of healthy individuals, and provides the basis for a detailed characterization of the oral mycobiome in health and disease.

Relatedness of medically important strains of Saccharomyces cerevisiae as revealed by phylogenetics and metabolomics

Ten medically important Saccharomyces strains, comprising six clinical isolates of Saccharomyces cerevisiae and four probiotic strains of Saccharomyces boulardii, were characterized at the genetic and metabolic level and compared with non-medical, commercial yeast strains used in baking and wine-making. Strains were compared by genetic fingerprinting using amplified fragment length polymorphism (AFLP) analysis, by ribosomal DNA ITS1 sequencing and by metabolic footprinting using both direct injection mass spectrometry (DIMS) and gas chromatography-time of flight-mass spectrometry (GC-ToF-MS). Overall, the clinical isolates fell into different groupings when compared with the non-medical strains, with good but not perfect correlation amongst strains at both the genetic and metabolic levels. Probiotic strains of S. boulardii that are used therapeutically to treat human gastro-intestinal tract disorders showed tight clustering both genetically and metabolically. Metabolomics was found to be of value both as a taxonomic tool and as a means to investigate anomalous links between genotype and phenotype. Key discriminatory metabolites were identified when comparing the three main groups of clinical, probiotic and non-medical strains and included molecules such as trehalose, myo-inositol, lactic acid, fumaric acid and glycerol 3-phosphate. This study confirmed the link between a subset of clinical isolates and baking or probiotic strains but also highlighted that in general the clinical strains were more diverse at both the genomic and metabolic levels.

Subgingival plaque microbiota in HIV positive patients

AIM

To describe and compare the predominant bacterial and fungal species associated with gingivitis, periodontitis, and linear gingival erythema (LGE), in HIV positive subjects with different immune status.

METHODS

Viral loads and CD4 levels determined HIV disease status. From pooled subgingival plaque, 16S and 18S rDNA were cloned and sequenced to determine species identity.

RESULTS

One hundred and nine bacterial species were identified from 14 subjects. Nearly half of the species were not cultivable. Notably, the classical putative periodontal pathogens, Treponema denticola, Porphyromonas gingivalis and Tannerella forsythia were below the limit of detection and were not detected. Species of Gemella, Dialister, Streptococcus and Veillonella were predominant. In one HIV positive subject with periodontitis and low viral load, Gemella morbillorum, a known opportunistic pathogen, constituted 84% of the clones. Saccharomyces cerevisiae was the only fungal species detected in an LGE subject and in periodontitis subjects with high viral loads. In periodontitis patients with low viral loads, Candida albicans was predominant, while S. cerevisiae was only a minor component.

CONCLUSION

These case studies suggest that other bacterial species, rather than the classical periodontal pathogens, may be involved in periodontal diseases of subjects with HIV. These data are indicative of opportunistic infections in a highly susceptible immunocompromised host.

Saccharomyces cerevisiae emboli in an immunocompromised patient with relapsed acute myeloid leukaemia

In humans, Saccharomyces cerevisiae (baker's yeast) is found infrequently as a commensal of mucosal surfaces and rarely causes infections. We describe a case of cutaneous septic emboli developing in a patient with relapsing acute myeloid leukaemia M6 who had recently been treated with clofarabine. Yeast forms were seen on skin biopsy and S. cerevisiae was isolated from her Hickman line. We are not aware of any previous case reports of cutaneous emboli associated with this organism.

Catalase activity in Candida albicans exposed to antineoplastic drugs

An increased catalase activity in Candida spp. has been suggested as a mechanism that reduces amphotericin B activity. Furthermore, resistance to antifungal agents like amphotericin B has been reported in some cancer patients undergoing chemotherapy treatment. In this study we analysed the influence of chemotherapy agents on catalase activity in Candida albicans, the major species involved in yeast infections. Eight strains of C. albicans isolated from HIV-positive patients were exposed to cyclophosphamide, cytarabine, dacarbazine and methotrexate antineoplastic drugs at the concentrations used during therapy. Catalase activity was measured and compared to the control group. Very significant differences (P < 0.01) were found when C. albicans was exposed to methotrexate (2 microg ml(-1) = 4 microM). For cyclophosphamide (50 microg ml(-1)), cytarabine (1 microg ml(-1)) and dacarbazine (8 microg ml(-1)), no differences were found (P > 0.05) between the control and drug-exposed groups. Although more extensive studies are necessary, these data do suggest that the antineoplastic drug methotrexate contributes to the resistance to antifungal drug therapy by varying catalase activity.

Immune response to Saccharomyces cerevisiae mannan conjugate in mice

Mannan, the surface polysaccharide antigen of Saccharomyces cerevisiae was partially oxidized and conjugated to a protein carrier. Prepared conjugate was immunogenic in mice and re-injection elicited significant increase of anti-S. cerevisiae specific IgG and IgM serum antibodies. There was somewhat less increase in IgM serum antibodies. Serum distribution of IgG subclasses, especially IgG(2(a+b)):IgG(1) ratio throughout the immunization demonstrated effective Th1 predominance of immune response. Newly synthesized S. cerevisiae mannan conjugate could be considered as a perspective vaccine candidate for preventive immunomodulation treatment.

Invasive Saccharomyces infection: a comprehensive review

BACKGROUND

Saccharomyces cerevisiae (also known as "baker's yeast" or "brewer's yeast") is mostly considered to be an occasional digestive commensal. However, since the 1990s, there have been a growing number of reports about its implication as an etiologic agent of invasive infection. A particular feature of such infections is their association with a probiotic preparation of Saccharomyces boulardii (a subtype of S. cerevisiae) for treatment various diarrheal disorders.

METHODS

We collected published case reports, through May 2005, of invasive Saccharomyces infection by use of a Medline query. Epidemiological and clinical charts and therapeutic strategies were analyzed.

RESULTS

We found 92 cases of Saccharomyces invasive infection. Predisposing factors were similar to those of invasive candidiasis, with intravascular catheter and antibiotic therapy being the most frequent. Blood was the most frequent site of isolation (for 72 patients). S. boulardii accounted for 51.3% of fungemias and was exclusively isolated from blood. Compared with patients infected with S. cerevisiae, patients infected with S. boulardii were more frequently immunocompetent and had a better prognosis. Saccharomyces invasive infection was clinically indistinguishable from an invasive candidiasis. Overall, S. cerevisiae clinical isolates exhibited low susceptibility to amphotericin B and azole derivatives. However, global outcome was favorable in 62% of the cases. Treatment with intravenous amphotericin B and fluconazole, in combination with central vascular catheter removal, were effective therapeutic options.

CONCLUSION

Saccharomyces organisms should now be added to the growing list of emerging fungal pathogens. Special caution should be taken regarding the use of S. boulardii probiotic preparations.

Saccharomyces cerevisiae fungemia: an emerging infectious disease

BACKGROUND

Saccharomyces cerevisiae is well known in the baking and brewing industry and is also used as a probiotic in humans. However, it is a very uncommon cause of infection in humans.

METHODS

During the period of 15-30 April 2003, we found 3 patients with S. cerevisiae fungemia in an intensive care unit (ICU). An epidemiological study was performed, and the medical records for all patients who were in the unit during the second half of April were assessed.

RESULTS

The only identified risk factor for S. cerevisiae infection was treatment with a probiotic containing Saccharomyces boulardii (Ultralevura; Bristol-Myers Squibb). This probiotic is used in Europe for the treatment and prevention of Clostridium difficile-associated diarrhea. The 3 patients received the product via nasograstric tube for a mean duration of 8.5 days before the culture result was positive, whereas only 2 of 41 control subjects had received it. Surveillance cultures for the control patients admitted at the same time did not reveal any carriers of the yeast. Strains from the probiotic capsules and the clinical isolates were identified as S. cerevisiae, with identical DNA fingerprinting. Discontinuation of use of the product in the unit stopped the outbreak of infection. A review of the literature identified another 57 cases of S. cerevisiae fungemia. Overall, 60% of these patients were in the ICU, and 71% were receiving enteral or parenteral nutrition. Use of probiotics was detected in 26 patients, and 17 patients died.

CONCLUSIONS

Use of S. cerevisiae probiotics should be carefully reassessed, particularly in immunosuppressed or critically ill patients.

In vitro susceptibility of yeasts isolated from patients in intensive care units to fluconazole and amphotericin B during a 3-year period

Fungal infections have increased dramatically in recent years and candidemia is a major risk factor for morbidity and mortality in intensive care units (ICUs). Candidemia has been considered to be a nosocomial infection that is strongly associated with neutropenia, recent surgery or presence of intravascular lines, and previous colonization is an independent risk factor. We evaluated the in vitro efficacy of fluconazole and amphotericin B against yeasts isolated from various clinical specimens of colonized or infected patients treated in the ICUs of the Institute of Cardiology, Istanbul University. A total of 1397 ICU patients were treated at the Institute of Cardiology between January 2000 and December 2002. A total of 117 yeasts isolated from 97 patients were included in this study. These ICU patients were hospitalized for a mean of 29 days. All yeasts were identified by conventional methods and using the API (20C AUX, ID 32C) system (Bio Meriéux, France). Susceptibility to fluconazole and amphotericin B was evaluated using the E-test (AB Biodisk, Solna, Sweden). The most commonly isolated yeast was Candida albicans (72.6%), followed by Candida tropicalis (16.2%), Candida kefyr, Candida krusei, Candida parapsilosis, Trichosporon mucoides and Geotrichum spp. Fluconazole and amphotericin B MIC90 values were 0.75 microg/ml; 0.19 microg/ml and 1 microg/ml; 0.38 microg/ml for C. albicans and C. tropicalis, respectively. All Geotrichum spp. were found to be susceptible-dose dependent (SDD) (MIC=16-32 microg/ml) to fluconazole. Two C. albicans, two C. tropicalis, one C. krusei and one Geotrichum spp. had a MIC value of > or = 0.38 microg/ml for amphotericin B. The rate of colonization was 3.36% (47/1397). Only 10 (0.71%) patients out of a total of 1397 developed candidemia during the period of the investigation. Of these, 7 (70%) were caused by non-albicans Candida spp.

Saccharomyces cerevisiae fungemia in a head and neck cancer patient: a case report and review of the literature

We report the case of a 65-year old male who developed Saccharomyces cerevisiae fungemia after completing a course of concomitant chemotherapy and radiation therapy for head and neck carcinoma. He had grade IV oral mucositis, and received Saccharomyces boulardii (Perenterol) orally as treatment for aseptic diarrhoea just before the onset of fungemia. We discuss the epidemiology and pathology of Saccharomyces cerevisiae in the cancer patient population.

Nosocomial transmission of Saccharomyces cerevisiae in bone marrow transplant patients

Saccharomyces cerevisiae is an unusual cause of clinical infection. We describe three bone marrow transplant patients on a haematology unit who developed possible invasive disease with the organism. Two patients died and both these patients appeared to have a related strain of S. cerevisiae. Screening for S. cerevisiae from throat and stool samples revealed four further patients who were carriers. Genotyping of the invasive and carriage strains demonstrated an indistinguishable strain from patients who had been on the unit at the same time, suggesting cross-infection.

Antimicrobial peptides: therapeutic potential for the treatment of Candida infections

The increasing frequency of fungal infections in immunocompromised patients together with the emergence of strains resistant to currently used antifungal drugs point to an increased need for a new class of antimycotics. Antimicrobial peptides are promising candidates for the treatment of fungal infections since they have both mechanisms of action distinct from available antifungal agents and the ability to regulate the host immune defence systems as well. This review focuses on Candida albicans as a large amount of work on the mechanisms of action of classical antifungals as well as antimicrobial peptides, such as defensins, protegrins, histatins and lactoferrin (LF)-derived peptides, has been performed in this yeast. Analogues of these antimicrobial peptides and combinations of antimicrobial peptides with classical antimycotics are under investigation for treatment of candidiasis.