Action of mycocins produced by Wickerhamomyces anomalus on Malassezia pachydermatis isolated from the ear canal of dogs.

This study aims to examine the effectiveness of mycocins produced by Wickerhamomyces anomalus in inhibiting Malassezia pachydermatis, a yeast commonly found in the ear canal of dogs. M. pachydermatis has a zoophilic origin and can be found in mammals, and frequently in dogs, where it mainly colonizes the ear canal region and the skin, leading to lesions that are difficult to treat. The antimicrobial mechanism was evaluated using dilutions of supernatant with enzymatic activity, which may include ß-glucanases, glycoproteins known to act on microorganism cell walls. However, it is important to note that this supernatant may contain other compounds as well. ß-glucanases in the mycocins supernatant were found at a concentration of 0.8 U/mg. The susceptibility of M. pachydermatis isolates was tested using the microdilution method. The isolates suffered 100% inhibition when tested with the culture supernatant containing mycocins. In the proteinases production test, 44% of the isolates tested were strong proteinases producers. Subsequently all these isolates suffered inhibition of their activity when tested in research medium containing mycocins supernatant at a subinhibitory concentration of ß-glucanases. This shows that mycocins can inhibit the production of proteinases, a virulence factor of M. pachydermatis. The viability test showed the antifungal action of mycocins in inhibiting the viability of M. pachydermatis cells after a period of 8  hours of contact. These results support the antimicrobial potential of mycocins and their promise as a therapeutic option.

Inhibition of Klebsiella pneumoniae carbapenemases by mycocins produced by Wickerhamomyces anomalus.

New alternatives have been under study as treatment due to the problem of multidrug-resistant bacteria. Among them, Wickerhamomyces anomalus mycocins have shown a great potential against several microorganisms since they have high antimicrobial activity, as well as they can be used as fast available nutrients and stand several extreme conditions. In this way, Klebsiella pneumoniae carbapenemases inhibition by mycocins produced by W. anomalus is important. Microdilution assays were carried out to evaluate strains inhibition in liquid medium and the test in solid medium were carried out. Toxicity was evaluated by both hemolysis and Artemia salina Leach tests. W. anomalus supernatant showed 2.36 U/mg ß-glucanases activity, and antimicrobial activity was evidenced in 100% Klebsiella pneumoniae carbapenemase strains up to 0.12 U/mg concentration. Besides, there was low toxicity in hemolysis and Artemia salina Leach tests. It is suggested that W. anomalus mycocins may be an alternative to develop new antimicrobial substances.

Production and Optimization of Killer Toxin in Debaryomyces hansenii Strains

ABSTRACT Postharvest diseases of fruits and vegetables result in critical losses of production in worldwide. The losses often are caused by fungi and nowadays, most fungal pathogens are controlled by several strategies such as the use of fungicides. However, most of the fungicides are chemical-based compounds and are dangerous to human health and the nature. Therefore, the discovery of healthy and reliable strategies is crucial to control of fungal pathogens. In the paper, it was aimed to evaluate and characterize yeast isolates previously isolated from dairy products for the production of killer toxin. A total of 18 yeasts have been found to produce antagonistic behavior against susceptible fungal species. All of the yeasts expressing killer character were characterized by using several molecular techniques, and isolates TEM8 and 17 identified as D. hansenii have showed the strongest antifungal activities. Improvement of killer toxin production by the yeasts also has been studied, and the highest production was found in YMB medium containing NaCl (6%) and DMSO (1000 ppm) at pH 4.0 and 20oC. The killer characters of these yeasts have indicated the potential use of the yeasts as antagonists for the control of postharvest diseases in agricultural industries.

Susceptibility of species within the Sporothrix schenckii complex to a panel of killer yeasts.

The Sporothrix schenckii complex is the etiologic agent of sporotrichosis, a subacute or chronic mycosis which can affect humans and animals. Killer yeasts have been used in the medical field for development of novel antimycotics and biotyping of pathogenic fungi. The action of 18 killer yeasts on the growth of 88 characterized S. schenckii, Sporothrix globosa, Sporothrix brasiliensis, and Sporothrix mexicana clinical and environmental isolates was evaluated. Killer studies were performed on Petri dishes containing cheese black starch agar. The yeasts Candida catenulata (QU26, QU31, QU127, LV102); Trichosporon faecale (QU100); Trichosporon japonicum (QU139); Kluyveromyces lactis (QU30, QU99, QU73); Kazachstania unispora (QU49), Trichosporon insectorum (QU89), and Kluyveromyces marxianus (QU103) showed activity against all strains of the S. schenckii complex tested. Observation by optical microscopy of S. brasiliensis 61 within the inhibition haloes around the colonies of the killer yeasts QU100, QU139, and LV102 showed that there was no conidiation, but there was hyphal proliferation. The toxins were fungistatic against S. brasiliensis 61. There was no difference in susceptibility to the toxins among the S. schenckii species complex. Further investigations are necessary to clearly establish the mechanism of action of the toxins.

Characterization of the Saccharomyces cerevisae Y500-4L killer toxin

The strain Saccharomyces cerevisiae Y500-4L, selected from the must of alcohol producing plants, liberates a toxin which is lethal to the commercial yeast produced by Fleischmann Royal Nabisco and other strains of yeast. This toxin was characterized, and the maximum production was obtained after 24 hours of incubation at 25ºC in YEPD medium. The maximum activity was achieved between pH 4.1 and 4.5 and between 22 and 25ºC and maximum stability in the pH range 3.8 to 4.5 at -10ºC. The killer toxin was inactivated by heating at 40ºC for 1 hour at pH 4.1. After concentration by ultrafiltration of culture supernatants and purification by gel filtration chromatography, the molecular weight of the purified toxin was estimated by SDS-PAGE to be about 18-20 kDa.

A linhagem de Saccharomyces cerevisiae Y500-4L, selecionada de mosto de fermentação de usina de álcool, produz toxina "killer", letal à levedura comercial Fleischmann Royal Nabisco e outras linhagens de leveduras. Esta proteína foi caracterizada, verificando-se que a produção máxima foi obtida após 24 horas de incubação a 25ºC em meio YEPD. A toxina "killer" apresentou maior atividade na faixa de pH 4,1-4,5 e temperatura de 22-25ºC; e maior estabilidade na faixa de pH 3,8-4,5 a -10ºC, sendo totalmente inativada após 1 hora de incubação a 40ºC em pH 4,1. Após concentração a partir do sobrenadante do meio de cultura através de ultrafiltração e purificação por cromatografia de filtração em gel, estimou-se, através de SDS-PAGE, que o peso molecular desta toxina é cerca de 18 a 20 kDa.