Comparisons of the Laccase Gene among Serotypes and Melanin-Deficient Variants ofCryptococcus neoformans

Trichophyton tonsurans strains from Brazil: phenotypic heterogeneity, genetic homology, and detection of virulence genes

The objective of this study was to establish the phenotypical and molecular patterns of clinical isolates of Trichophyton tonsurans circulating in the state of Ceará, northeastern Brazil. For this purpose, 25 T. tonsurans strains isolated from independent cases of tinea capitis in children were phenotypically evaluated regarding their macro- and micro-morphological characteristics, vitamin requirements, urease production, and antifungal susceptibility. The molecular characterization was carried out with random amplified polymorphic DNA molecular markers and M13 fingerprinting. The presence of the genes CarbM14, Sub2, CER, URE, ASP, PBL, and LAC, which encode enzymes related to fungal virulence, was also evaluated. Finally, melanin production was assessed through specific staining. The data obtained demonstrated that these T. tonsurans strains have considerable phenotypical variation, although they showed a low degree of genetic polymorphism according to the markers used. The genes CarbM14, Sub2, CER, and URE were detected in all the analyzed strains. The gene LAC was also identified in all the strains, and melanin synthesis was phenotypically confirmed. The strains were susceptible to antifungals, especially itraconazole (GM = 0.06 μg/mL) and ketoconazole (GM = 0.24 μg/mL). Therefore, T. tonsurans strains can present great phenotypical heterogeneity, even in genetically similar isolates. Moreover, the presence of the LAC gene indicates the possible participation of melanin in the pathogenesis of these dermatophytes.

Diversity of laccase among Cryptococcus neoformans serotypes

The pathogenic yeast C. neoformans is classified into three varieties with five serotypes; var. grubii (serotype A), var. neoformans (serotype D), var. gattii (serotypes B and C), and serotype AD. Melanin is a virulence factor in the species, and its biosynthesis is catalyzed by laccase, encoded by the LAC1 gene. In order to estimate the natural variability of the LAC1 gene among Cryptococcus serotypes, the laccase protein sequence from 55 strains was determined and the phylogenetic relationships between cryptococcal and related fungal laccases revealed. The deduced laccase proteins consisted of 624 amino acid residues in serotypes A, D and AD, and 613 to 615 residues in serotypes B and C. Intra-serotype amino acid variation was marginal within serotypes A and D, and none was found within serotypes AD and C. Maximum amino acid replacement occurred in two serotype B strains. The similarity in the deduced sequence ranged from 80 to 96% between serotypes. The sequence in the copper-binding regions was strongly conserved in the five serotypes. The laccases of the five serotypes were grouped together in the same clade of the phylogenetic tree reconstructed from different fungal laccases, suggesting a monophyletic clade.

Serotype identification of Cryptococcus neoformans by multiplex PCR

The pathogenic yeast Cryptococcus neoformans is traditionally classified into three varieties with five serotypes: var. grubii (serotype A), var. neoformans (serotype D), var. gattii (serotypes B and C) and serotype AD (hybrid of serotypes A and D). A commercial kit, Crypto Check (Iatron Laboratories, Tokyo, Japan), has been used worldwide for serotyping isolated strains. However, its production was discontinued in 2004, and hence the present study aimed to develop a simple polymerase chain reaction (PCR) method for serotyping C. neoformans strains. Subjecting genomic DNA of 59 strains of the five serotypes to multiplex PCR amplification using a set of four primers designed for the laccase gene (LAC1) differentiated serotypes A, D, B and C, but could not separate serotype AD from serotype D. However, a primer pair designed for the capsule gene (CAP64) allowed serotypes D and AD to be differentiated. When PCR amplification was performed in the simultaneous presence of the above six primers, the five serotypes produced two to five DNA fragments that could be used to distinguish them. This multiplex PCR method is useful for serotyping C. neoformans isolates, and represents an effective replacement for the Crypto Check kit.

Dual infections with pigmented and albino strains of Cryptococcus neoformans in patients with or without human immunodeficiency virus infection in India

Cryptococcus neoformans is an encapsulated yeast-like fungus of worldwide distribution. Melanin production is an important virulence factor of C. neoformans. We report the identification of distinct cryptococcal isolates with either pigmented or white colony phenotypes on L-dihydroxyphenylalanine agar plates in three patients who presented with meningitis to the All India Institute of Medical Sciences in India. Two of the patients were also infected with human immunodeficiency virus. Biochemical studies, India ink analysis, immunofluorescence with antibodies specific to capsular antigen, and serotyping confirmed that the melanotic and albino strains were C. neoformans serotypes A and D, respectively. Genotyping with M13 and [GACA]4 primers revealed that all the C. neoformans isolates were genetically different. The CNLAC1 gene associated with melanin production was identified in all the strains by PCR. Standard MIC testing revealed that the strains had similar susceptibilities to amphotericin B, but time-kill assays with the antifungal showed reduced susceptibility in melanin-producing strains. Infection studies with A/Jcr mice showed that the melanin-lacking yeast were less virulent than melanin-producing isolates. These findings indicate that these patients had dual infections with pigmented and albino strains of C. neoformans that were phenotypically and biologically different. Continued surveillance of primary isolates from patients with cryptococcosis by analyzing phenotypic differences and by molecular methods may reveal that mixed infections occur more commonly than is currently realized.