Baker's yeast as adjunctive therapy for relapses of Clostridium difficile diarrhea

Novel insights in genetic transformation of the probiotic yeast Saccharomyces boulardii

Saccharomyces boulardii (S. boulardii) is a probiotic yeast related to Saccharomyces cerevisiae (S. cerevisiae) but with distinct genetic, taxonomic and metabolic properties. S. cerevisiae has been used extensively in biotechnological applications. Currently, many strains are available, and multiple genetic tools have been developed, which allow the expression of several exogenous proteins of interest with applications in the fields of medicine, biofuels, the food industry, and scientific research, among others. Although S. boulardii has been widely studied due to its probiotic properties against several gastrointestinal tract disorders, very few studies addressed the use of this yeast as a vector for expression of foreign genes of interest with biotechnological applications. Here we show that, despite the similarity of the two yeasts, not all genetic tools used in S. cerevisiae can be applied in S. boulardii. While transformation of the latter could be obtained using a commercial kit developed for the former, consequent screening of successful transformants had to be optimized. We also show that several genes frequently used in genetic manipulation of S. cerevisiae (e.g., promoters and resistance markers) are present in S. boulardii. Sequencing revealed a high rate of homology (> 96%) between the orthologs of the two yeasts. However, we also observed some of them are not eligible to be targeted for transformation of S. boulardii. This work has important applications toward the potential of this probiotic yeast as an expression system for genes of interest.

Neutralization of Clostridium difficile toxin A using antibody combinations

The pathogenicity of Clostridium difficile (C. difficile) is mediated by the release of two toxins, A and B. Both toxins contain large clusters of repeats known as cell wall binding (CWB) domains responsible for binding epithelial cell surfaces. Several murine monoclonal antibodies were generated against the CWB domain of toxin A and screened for their ability to neutralize the toxin individually and in combination. Three antibodies capable of neutralizing toxin A all recognized multiple sites on toxin A, suggesting that the extent of surface coverage may contribute to neutralization. Combination of two noncompeting antibodies, denoted 3358 and 3359, enhanced toxin A neutralization over saturating levels of single antibodies. Antibody 3358 increased the level of detectable CWB domain on the surface of cells, while 3359 inhibited CWB domain cell surface association. These results suggest that antibody combinations that cover a broader epitope space on the CWB repeat domains of toxin A (and potentially toxin B) and utilize multiple mechanisms to reduce toxin internalization may provide enhanced protection against C. difficile-associated diarrhea.

Systematic review and meta-analysis of Saccharomyces boulardii in adult patients

This article reviews the evidence for efficacy and safety of Saccharomyces boulardii (S. boulardii) for various disease indications in adults based on the peer-reviewed, randomized clinical trials and pre-clinical studies from the published medical literature (Medline, Clinical Trial websites and meeting abstracts) between 1976 and 2009. For meta-analysis, only randomized, blinded controlled trials unrestricted by language were included. Pre-clinical studies, volunteer studies and uncontrolled studies were excluded from the review of efficacy and meta-analysis, but included in the systematic review. Of 31 randomized, placebo-controlled treatment arms in 27 trials (encompassing 5029 study patients), S. boulardii was found to be significantly efficacious and safe in 84% of those treatment arms. A meta-analysis found a significant therapeutic efficacy for S. boulardii in the prevention of antibiotic-associated diarrhea (AAD) (RR = 0.47, 95% CI: 0.35-0.63, P < 0.001). In adults, S. boulardii can be strongly recommended for the prevention of AAD and the traveler's diarrhea. Randomized trials also support the use of this yeast probiotic for prevention of enteral nutrition-related diarrhea and reduction of Helicobacter pylori treatment-related symptoms. S. boulardii shows promise for the prevention of C. difficile disease recurrences; treatment of irritable bowel syndrome, acute adult diarrhea, Crohn's disease, giardiasis, human immunodeficiency virus-related diarrhea; but more supporting evidence is recommended for these indications. The use of S. boulardii as a therapeutic probiotic is evidence-based for both efficacy and safety for several types of diarrhea.

Saccharomyces cerevisiae: population divergence and resistance to oxidative stress in clinical, domesticated and wild isolates

BACKGROUND

Saccharomyces cerevisiae has been associated with human life for millennia in the brewery and bakery. Recently it has been recognized as an emerging opportunistic pathogen. To study the evolutionary history of S. cerevisiae, the origin of clinical isolates and the importance of a virulence-associated trait, population genetics and phenotypic assays have been applied to an ecologically diverse set of 103 strains isolated from clinics, breweries, vineyards, fruits, soil, commercial supplements and insect guts.

METHODOLOGY/PRINCIPAL FINDINGS

DNA sequence data from five nuclear DNA loci were analyzed for population structure and haplotype distribution. Additionally, all strains were tested for survival of oxidative stress, a trait associated with microbial pathogenicity. DNA sequence analyses identified three genetic subgroups within the recombining S. cerevisiae strains that are associated with ecology, geography and virulence. Shared alleles suggest that the clinical isolates contain genetic contribution from the fruit isolates. Clinical and fruit isolates exhibit high levels of recombination, unlike the genetically homogenous soil isolates in which no recombination was detected. However, clinical and soil isolates were more resistant to oxidative stress than any other population, suggesting a correlation between survival in oxidative stress and yeast pathogenicity.

CONCLUSIONS/SIGNIFICANCE

Population genetic analyses of S. cerevisiae delineated three distinct groups, comprising primarily the (i) human-associated brewery and vineyard strains, (ii) clinical and fruit isolates (iii) and wild soil isolates from eastern U.S. The interactions between S. cerevisiae and humans potentiate yeast evolution and the development of genetically, ecologically and geographically divergent groups.

Screening of yeasts as probiotic based on capacities to colonize the gastrointestinal tract and to protect against enteropathogen challenge in mice

Probiotics are defined as viable microorganisms that exhibit a beneficial effect on the host's health when they are ingested. Two important criteria are used for selection of probiotic microorganisms: they must be able to survive in the gastrointestinal environment and to present at least one beneficial function (colonization resistance, immunomodulation or nutritional contribution). Generally, in vitro assays demonstrating these properties were used to select probiotics but it is unclear if the data can be extrapolated to in vivo conditions. In the present work, twelve Saccharomyces cerevisiae strains isolated from different environments (insect association, tropical fruit, cheese and "aguardente" production) and pre-selected for in vitro resistance to simulated gastrointestinal conditions were inoculated in germ-free mice to evaluate their real capacity to colonize the mammal digestive tract. Using these data, one of the yeasts (S. cerevisiae 905) was selected and tested in gnotobiotic (GN) and conventional (CV) mice for its capacity to protect against oral challenge with two enteropathogenic bacteria (Salmonella Typhimurium and Clostridium difficile). The yeast reached populational levels potentially functional in the gastrointestinal portions where the enteropathogens tested act. No antagonism against either pathogenic bacterium by the yeast was observed in the digestive tract of GN mice but, after challenge with S. Typhimurium, mortality was lower and liver tissue was better preserved in CV animals treated with the yeast when compared with a control group (p<0.05). Histopathological results of intestines showed that the yeast also presented a good protective effect against oral challenge with C. difficile in GN mice (p<0.05). In conclusion, among the 12 S. cerevisiae tested, strain 905 showed the best characteristics to be used as a probiotic as demonstrated by survival capacity in the gastrointestinal tract and protective effect of animals during experimental infections.

Pseudomembranous colitis in children

This review presents the microbiology, management and prevention of pseudomembranous colitis (PMC) in children. PMC is commonly associated with prior antibiotic exposure and hospitalization. It is caused almost exclusively by toxins produced by Clostridium difficile. The clinical spectrum of this disease may range from a mild, non-specific diarrhea to severe colitis with toxic megacolon, perforation, and death. PMC may affect all age groups, although a lower incidence has been noted in children. Ampicillin, amoxicillin, the second- and third-generation cephalosporins and clindamycin are the drugs most frequently associated with development of PMC, although nearly all antimicrobials have been implicated as causes of diarrhea and colitis. Discontinuation of antibiotics and supportive therapy usually lead to resolution of this disorder. Administration of oral vancomycin or other therapeutic regimens may be needed.

Clostridium difficile

Clostridium difficile is a major cause of antibiotic-associated diarrhea and colitis. The incidence of infection with this organism is increasing in hospitals worldwide, consequent to the widespread use of broad-spectrum antibiotics. Pathogenic strains of C. difficile produce two protein exotoxins, toxin A and toxin B, that cause colonic mucosal injury and inflammation. Many patients who are colonized are asymptomatic, and recent evidence indicates that diarrhea and colitis occur in those individuals who lack a protective antitoxin immune response. In patients who do develop symptoms, the spectrum of C. difficile disease ranges from mild diarrhea to fulminant pseudomembranous colitis. Prevention of nosocomial C. difficile infection involves judicious use of antibiotics and multidisciplinary infection control measures to reduce environmental contamination and patient cross-infection. Ultimately, active or passive immunization against C. difficile may be an effective means of controlling the growing problem of nosocomial C. difficile diarrhea and colitis.

Adherence of Escherichia coli serogroup O 157 and the Salmonella typhimurium mutant DT 104 to the surface of Saccharomyces boulardii

The detection of lectin sites for mannose-sensitive adhesion in the outer membrane of Saccharomyces boulardii and the irreversible binding of both enteropathogenic Escherichia coli (EPEC) and salmonellae (serovar Salmonella Typhimurium and Salmonella Enteritidis) provided the motivation to carry out further investigations to find out whether also other enteric bacteria such as entero-haemorrhagic Escherichia coli (EHEC) and the DT 104 mutant of S. Typhimurium have the capacity for binding to the cell wall of this yeast. Reference strains and fresh isolates from clinical cases of EHEC infections as well as salmonellae of the DT 104 mutant were included in this study using the agglutination test. The results first of all showed that EHEC of the serogroup O 157 and the DT 104 mutant of S. Typhimurium were bound to the surface of Saccharomyces boulardii. Because these bacteria do not respond very well to drugs but most of the gastrointestinal infections are caused by them, the use of S. boulardii for treatment and prophylaxis could be an excellent alternative.

Species identification and virulence attributes of Saccharomyces boulardii (nom. inval.)

Saccharomyces boulardii (nom. inval.) has been used for the treatment of several types of diarrhea. Recent studies have confirmed that S. boulardii is effective in the treatment of diarrhea, in particular chronic or recurrent diarrhea, and furthermore that it is a safe and well-tolerated treatment. The aim of the present study was to identify strains of S. boulardii to the species level and assess their virulence in established murine models. Three strains of S. boulardii were obtained from commercially available products in France and Italy. The three S. boulardii strains did not form spores upon repeated testing. Therefore, classical methods used for the identification of Saccharomyces spp. could not be undertaken. Typing by using the restriction fragment length polymorphisms (RFLPs) of the PCR-amplified intergenic transcribed spacer regions (including the 5. 8S ribosomal DNA) showed that the three isolates of S. boulardii were not separable from authentic isolates of Saccharomyces cerevisiae with any of the 10 restriction endonucleases assessed, whereas 9 of the 10 recognized species of Saccharomyces could be differentiated. RFLP analysis of cellular DNA with EcoRI showed that all three strains of S. boulardii had identical patterns and were similar to other authentic S. cerevisiae isolates tested. Therefore, the commercial strains of S. boulardii available to us cannot be genotypically distinguished from S. cerevisiae. Two S. boulardii strains were tested in CD-1 and DBA/2N mouse models of systemic disease and showed intermediate virulence compared with virulent and avirulent strains of S. cerevisiae. The results of the present study show that these S. boulardii strains are asporogenous strains of the species S. cerevisiae, not representatives of a distinct and separate species, and possess moderate virulence in murine models of systemic infection. Therefore, caution should be advised in the clinical use of these strains in immunocompromised patients until further study is undertaken.

Intracellular signal triggered by cholera toxin in Saccharomyces boulardii and Saccharomyces cerevisiae

As is the case for Saccharomyces boulardii, Saccharomyces cerevisiae W303 protects Fisher rats against cholera toxin (CT). The addition of glucose or dinitrophenol to cells of S. boulardii grown on a nonfermentable carbon source activated trehalase in a manner similar to that observed for S.cerevisiae. The addition of CT to the same cells also resulted in trehalase activation. Experiments performed separately on the A and B subunits of CT showed that both are necessary for activation. Similarly, the addition of CT but not of its separate subunits led to a cyclic AMP (cAMP) signal in both S. boulardii and S. cerevisiae. These data suggest that trehalase stimulation by CT probably occurred through the cAMP-mediated protein phosphorylation cascade. The requirement of CT subunit B for both the cAMP signal and trehalase activation indicates the presence of a specific receptor on the yeasts able to bind to the toxin, a situation similar to that observed for mammalian cells. This hypothesis was reinforced by experiments with 125I-labeled CT showing specific binding of the toxin to yeast cells. The adhesion of CT to a receptor on the yeast surface through the B subunit and internalization of the A subunit (necessary for the cAMP signal and trehalase activation) could be one more mechanism explaining protection against the toxin observed for rats treated with yeasts.

Intracellular signal triggered by cholera toxin in Saccharomyces boulardii and Saccharomyces cerevisiae

As is the case for Saccharomyces boulardii, Saccharomyces cerevisiae W303 protects Fisher rats against cholera toxin (CT). The addition of glucose or dinitrophenol to cells of S. boulardii grown on a nonfermentable carbon source activated trehalase in a manner similar to that observed for S.cerevisiae. The addition of CT to the same cells also resulted in trehalase activation. Experiments performed separately on the A and B subunits of CT showed that both are necessary for activation. Similarly, the addition of CT but not of its separate subunits led to a cyclic AMP (cAMP) signal in both S. boulardii and S. cerevisiae. These data suggest that trehalase stimulation by CT probably occurred through the cAMP-mediated protein phosphorylation cascade. The requirement of CT subunit B for both the cAMP signal and trehalase activation indicates the presence of a specific receptor on the yeasts able to bind to the toxin, a situation similar to that observed for mammalian cells. This hypothesis was reinforced by experiments with 125I-labeled CT showing specific binding of the toxin to yeast cells. The adhesion of CT to a receptor on the yeast surface through the B subunit and internalization of the A subunit (necessary for the cAMP signal and trehalase activation) could be one more mechanism explaining protection against the toxin observed for rats treated with yeasts.

Clostridium difficile infection

The spore-forming anaerobe Clostridium difficile has become a serious enteropathogen. Changes in the composition of natural intestinal flora, mainly due to antibiotic therapy, permit its colonization of, and multiplication in, the colon. The disease is caused by (entero)toxin A and (cyto)toxin B, and infection ranges from asymptomatic carrier state and mild diarrhea to pseudomembranous colitis. The clinical diagnosis is made by observing inflammatory, sometimes bloody, diarrhea and by the colonoscopic detection of epithelial necrosis, ulceration, and, in the advanced state, pseudomembrane formation. The laboratory supports the diagnosis by detecting toxin A and/or B by an enzyme-linked immunoassay with high specificity, but sometimes less sensitivity than with the cytotoxin assay in tissue culture cells. Fecal leukocytes or fecal lactoferrin may be found. Culture for the isolation and identification of toxigenic C. difficile is time consuming but necessary for epidemiological studies. Polymerase chain reaction (PCR) tests have been tested for detection of the toxin B gene directly in stool. Therapy consists of stopping all systemic antibiotic treatment and the use of oral metronidazole or vancomycin. There may be more relapses after vancomycin therapy, and the increasing vancomycin resistance of Enterococcus is worrisome. Prevention, especially of nosocomial spread, requires isolation and enforced handwashing. For epidemiological studies, the bacteria can be typed by molecular DNA analyses, including PCR, protein electrophoresis, and immunological tests.