Cryptococcus neoformans and Cryptococcus gattii are encapsulated basidiomycetous yeasts that cause meningoencephalitis. The action of killer yeasts on the growth of one hundred genotypically characterized C. neoformans var. neoformans, C. neoformans var. grubii, and C. gattii clinical and environmental isolates was evaluated. Killer studies were performed on yeast malt-methylene blue (YM-MB) agar Petri dishes, and a dendrogram was obtained based on a quantitative data matrix using the diameter of the inhibition halo. The cellular morphological characteristics of dead cells within the halo were observed by means of optical and scanning electron microscopy. There was no formation of pores on the cell surface of the sensitive cells in contact with the toxins, at least for C. neoformans. The sensitivity patterns of clinical and environmental isolates to the killer toxins demonstrated that there is correlation between killer sensitivity of Cryptococcus species or varieties and some of the killer strains. In this case, the isolates were discriminated using the killer sensitivity patterns, and this could be used as a complementary tool to PCR-fingerprinting in epidemiological studies.
Discrimination of multi-resistant microorganisms in small clinical microbiology laboratories is frequently based on the biologic profile (biotype) of phenotypic markers, such as antimicrobial susceptibility patterns (antibiograms) and serologic or enzymatic typing, but few use indicative microorganisms. The purpose of this study was to evaluate the power of a panel of selected killer yeasts for differentiating and discriminating clinical isolates of Staphylococcus epidermidis from two care hospitals and clinical microbiology laboratories from the South of Brazil. The short panel of eleven killer yeasts was capable of discriminating 100% of the sensitive strains of S. epidermidis using quantitative data matrix (QDM) and differentiating them from strains of coagulase-positive Staphylococcus. Therefore, this phenotypic methodology proved to be valid as a discriminatory tool when applied to these clinical bacteria strains, besides being simple and feasible for routine use even in microbiological laboratories with minimal resources.
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