Lethality of yeasts with low pathogenicity in mice immunocompromised by cyclophosphamide treatment

Activity of the pterophyllins 2 and 4 against postharvest fruit pathogenic fungi. Comparison with a synthetic analog and related intermediates

The antifungal activity of pterophyllin 2, pterophyllin 4, a 5-desmethyl analog of the latter and some of their synthetic intermediates, against three postharvest phytopathogenic fungi, was evaluated. The target fungi were Rhizopus stolonifer, Botrytis cinerea and Monilinia fructicola, which affect fruits worldwide, causing important economic losses. The tests were carried out with imazalil and carbendazim as positive controls. Minimum inhibitory concentrations and minimum fungicidal concentrations were determined, and the morphology of the colonies was examined microscopically. In liquid medium, it was found that pterophyllin 4 exhibited selective fungicidal activity toward M. fructicola, whereas its congener pterophyllin 2 proved to be less potent and not selective and the 5-desmethyl analog of pterophyllin 4 displayed a different activity profile. Morphological changes were observed in the colonies exposed to pterophyllin 4. The results highlighted the importance of small structural features for the antifungal behavior and also suggested that, in Nature, the pterophyllins may act as plant defenses against pathogens.

In vivo virulence of commercial Saccharomyces cerevisiae strains with pathogenicity-associated phenotypical traits

Two commercial Saccharomyces cerevisiae strains, a baker's strain and the bio-therapeutic agent Ultralevure, have been proposed as a possible exogenous source of human colonization (de Llanos et al., 2004, 2006a). Moreover, these strains express phenotypical traits associated to pathogenicity (de Llanos et al., 2006b). Taking into account that both commercial preparations represent an important source of living S. cerevisiae cells we have performed an in vivo study to evaluate whether there is a potential safety risk to humans. Their virulence was compared with that of other commercial strains with less virulent traits, and with clinical isolates, using two murine models (BALB/c and DBA/2N mice). Burden determination in the brain and kidneys showed that the ability to disseminate, colonize and persist was manifested not only by clinical isolates but also by commercial strains. Among these, the baker's strain and Ultralevure were able to cause the death of BALB/c mice at rates similar to those shown by two of the clinical isolates. These results highlight the pathogenic potential of these strains and show that four-week-old BALB/c mice are an appropriate murine model to study the virulence of yeasts with low or moderate pathogenicity. Furthermore, we have shown the positive effect of an immunosuppressive therapy with cyclophosphamide in the virulence of the baker's strains and Ultralevure but not in the rest of the commercial strains under study. The data suggest that although S. cerevisiae has always been considered a GRAS microorganism, commercial preparations should include only those strains shown to be safe in order to minimize complications in risk groups.