Cryptococcus neoformans {alpha} strains preferentially disseminate to the central nervous system during coinfection

Cryptococcus neoformans is a fungal pathogen that has evolved over the past 40 million years into three distinct varieties or sibling species (gattii, grubii, and neoformans). Each variety manifests differences in epidemiology and disease, and var. grubii strains are responsible for the vast majority of human disease. In previous studies, alpha strains were more virulent than congenic a strains in var. neoformans, whereas var. grubii congenic a and alpha strains exhibited equivalent levels of virulence. Here the role of mating type in the virulence of var. grubii was further characterized in a panel of model systems. Congenic var. grubii a and alpha strains had equivalent survival rates when cultured with amoebae, nematodes, and macrophages. No difference in virulence was observed between a and alpha congenic strains in multiple inbred-mouse genetic backgrounds, and there was no difference in accumulations in the central nervous system (CNS) late in infection. In contrast, during coinfections, a and alpha strains are equivalent in peripheral tissues but alpha cells have an enhanced predilection to penetrate the CNS. These studies reveal the first virulence difference between congenic a and alpha strains in the most common pathogenic variety and suggest an explanation for the prevalence of alpha strains in clinical isolates.     

Molecular genetic analyses of mating pheromones reveal intervariety mating or hybridization in Cryptococcus neoformans

The sexual mating of the pathogenic yeast Cryptococcus neoformans is important for pathogenesis studies because the fungal virulence is linked to the alpha mating type (MAT(alpha)). We characterized C. neoformans mating pheromones (MF(alpha) 1 and MFa1) from 122 strains to understand intervariety hybridization or mating and intervariety virulence. MF(alpha) 1 in three C. neoformans varieties showed (a) specific nucleotide polymorphisms, (b) different copy numbers and chromosomal localizations, and (c) unique deduced amino acids in two geographic populations of C. neoformans var. gattii. MF(alpha) 1 of different varieties cross-hybridized in Southern hybridizations. Their phylogenetic analyses showed purifying selection (neutral evolution). These observations suggested that MAT(alpha) strains from any of the three C. neoformans varieties could mate or hybridize in nature with MATa strains of C. neoformans var. neoformans. A few serotype A/D diploid strains provided evidence for mating or hybridization, while a majority of A/D strains tested positive for haploid MF(alpha) 1 identical to that of C. neoformans var. grubii. MF(alpha) 1 sequence and copy numbers in diploids were identical to those of C. neoformans var. grubii, while their MFa1 sequences were identical to those of C. neoformans var. neoformans; thus, these strains were hybrids. The mice survival curves and histological lesions revealed A/D diploids to be highly pathogenic, with pathogenicity levels similar to that of the C. neoformans var. grubii type strain and unlike the low pathogenicity levels of C. neoformans var. neoformans strains. In contrast to MF(alpha) 1 in three varieties, MFa1 amplicons and hybridization signals could be obtained only from two C. neoformans var. neoformans reference strains and eight A/D diploids. This suggested that a yet undiscovered MFa pheromone(s) in C. neoformans var. gattii and C. neoformans var. grubii is unrelated to, highly divergent from, or rarer than that in C. neoformans var. neoformans. These observations could form the basis for future studies on the role of intervariety mating in C. neoformans biology and virulence.     

Isolation of Cryptococcus gattii and Cryptococcus neoformans var. grubii from the flowers and bark of Eucalyptus trees in India.

The association of Cryptococcus gattii with Eucalyptus trees has been well established. Here we report the isolation of both C. gattii and Cryptococcus neoformans var. grubii from the flowers and bark of Eucalyptus trees in India. We investigated a total of 233 samples of Eucalyptus trees: 120 flowers, 81 fragments of bark, and 32 leaves. C. gattii was isolated from two samples of flowers of Eucalyptus terreticornis. C. neoformans var. grubii was recovered twice from the bark of Eucalyptus camaldulensis, initially from one of three samples, and again 2 months later, from one of four samples collected beneath the canopy of the tree. The primary isolation medium was Nigerseed agar, and brown colonies were presumptively identified as C. gattii or C. neoformans. The species identification was confirmed by morphological and biochemical characteristics. Using the Crypto-Check kit (Iatron, Tokyo, Japan), the first two isolates were identified as serotype B (C. gattii) and the other two were serotype A (C. neoformans var. grubii). PCR analysis of the isolates of C. neoformans var. grubii revealed that they possessed the MATalpha mating type allele. Molecular typing by amplified fragment length polymorphism markers indicated that both isolates of C. neoformans var. grubii possessed the same genotype. This study demonstrates that C. neoformans var. grubii, as well as C. gattii, may be associated with Eucalyptus trees.     

Experimental systemic infection with Cryptococcus neoformans var. grubii and Cryptococcus gattii in normal and immunodeficient mice.

Cryptococcus neoformans (Cn) var. grubii or Cryptococcus neoformans var. neoformans infection is usually associated with immunocompromised hosts, whereas Cryptococcusgattii more frequently causes disease in immunocompetent hosts. We examined the effects of immunodeficiency and glucocorticoid-induced immunosuppression on systemic murine infection induced by i.v. inoculation with these pathogens. SCID and immunocompetent BALB/c and C57BL/6 mice were infected with 相似文献   

Typing and patterns of cellular morphological alterations in Cryptococcus neoformans and Cryptococcus gattii isolates exposed to a panel of killer yeasts.

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.     

Rapid identification of Cryptococcus neoformans var. grubii, C. neoformans var. neoformans, and C. gattii by use of rapid biochemical tests, differential media, and DNA sequencing

Rapid identification of Cryptococcus neoformans var. grubii, Cryptococcus neoformans var. neoformans, and Cryptococcus gattii is imperative for facilitation of prompt treatment of cryptococcosis and for understanding the epidemiology of the disease. Our purpose was to evaluate a test algorithm incorporating commercial rapid biochemical tests, differential media, and DNA sequence analysis that will allow us to differentiate these taxa rapidly and accurately. We assessed 147 type, reference, and clinical isolates, including 6 other Cryptococcus spp. (10 isolates) and 14 other yeast species (24 isolates), using a 4-hour urea broth test (Remel), a 24-hour urea broth test (Becton Dickinson), a 4-hour caffeic acid disk test (Hardy Diagnostics and Remel), 40- to 44-hour growth assessment on l-canavanine glycine bromothymol blue (CGB) agar, and intergenic spacer (IGS) sequence analysis. All 123 Cryptococcus isolates hydrolyzed urea, along with 7 isolates of Rhodotorula and Trichosporon. Eighty-five of 86 C. neoformans (99%) and 26 of 27 C. gattii (96%) isolates had positive caffeic acid results, unlike the other cryptococci (0/10) and yeast species (0/24). Together, these two tests positively identified virtually all C. neoformans/C. gattii isolates (98%) within 4 h. CGB agar or IGS sequencing further differentiated these isolates within 48 h. On CGB, 25 of 27 (93%) C. gattii strains induced a blue color change, in contrast to 0 of 86 C. neoformans isolates. Neighbor-joining cluster analysis of IGS sequences differentiated C. neoformans var. grubii, C. neoformans var. neoformans, and C. gattii. Based on these results, we describe a rapid identification algorithm for use in a microbiology laboratory to distinguish clinically relevant Cryptococcus spp.     

Urease inhibition by EDTA in the two varieties of Cryptococcus neoformans.

Cryptococcus neoformans var. neoformans (74 isolates) and C. neoformans var. gattii (44 isolates) were used to test urease activity after growth on both yeast extract-glucose-peptone agar (YEPG) and on YEPG supplemented with 100 microM EDTA. Every isolate grown on YEPG agar for 48 h at 30 degrees C produced a positive reaction within 1 h in a modified rapid urease assay at 37 degrees C. However, isolates grown on YEPG with 100 microM EDTA showed a distinct pattern which corresponded to their varietal status. All but 1 of 74 C. neoformans var. neoformans isolates (98.7%) produced a positive reaction within 1 to 4 h, while none of 44 C. neoformans var. gattii isolates produced a positive reaction within the same period. The urease inhibition results and the canavanine-glycine-bromthymol blue agar test results showed 100% correlation among isolates of C. neoformans var. gattii and 98.7% correlation among isolates of C. neoformans var. neoformans. Two representative isolates of C. neoformans var. gattii (serotypes B and C) were further tested for urease during a prolonged incubation period in urea broth. These isolates failed to show a positive reaction even after 11 h of incubation. The uptake of EDTA was negligible in the two varieties. Extracts of cells grown on YEPA agar showed a high level of urease activity in both varieties. Extracts of cells grown on the agar with 100 microM EDTA showed a marked reduction (86%) of urease activity in one isolate of C. neoformans var. gattii but showed only a 30% reduction in one isolate of C. neoformans var. neoformans. Based on these results, the differential effect of EDTA on the two varieties of C. neoformans appeared to be due to greater inhibition of urease synthesis in C. neoformans var. gattii.     

Molecular epidemiology of clinical Cryptococcus neoformans strains from India

Little is known about the molecular epidemiology of the human pathogenic fungus Cryptococcus neoformans in India, a country now in the midst of an epidemic of AIDS-related cryptococcosis. We studied 57 clinical isolates from several regions in India, of which 51 were C. neoformans var. grubii, 1 was C. neoformans var. neoformans, and 5 were C. neoformans var. gattii. This strain set included 18 additional sequential isolates from 14 patients. Strains were characterized phenotypically by measuring the polysaccharide capsule and by determining the MICs of standard antifungals. Molecular typing was performed by a PCR-based method using the minisatellite-specific core sequence (M13), by electrophoretic karyotyping, by restriction fragment length polymorphisms with the C. neoformans transposon 1 (TCN-1), and by URA5 DNA sequence analysis. Overall, Indian isolates were less heterogeneous than isolates from other regions and included a subset that clustered into one group based on URA5 DNA sequence analysis. In summary, our results demonstrate (i) differences in genetic diversity of C. neoformans isolates from India compared to isolates from other regions in the world; (ii) that DNA typing with the TCN-1 probe can adequately distinguish C. neoformans var. grubii strains; (iii) that TCN-1 sequences are absent in many C. neoformans var. gattii strains, supporting previous studies indicating that these strains have a limited geographical dispersal; and (iv) that human cryptococcal infection can be associated with microevolution of the infecting strain and by simultaneous coinfection with two distinct C. neoformans strains.     

Serotyping of Cryptococcus neoformans by using a monoclonal antibody specific for capsular polysaccharide.

The importance of epidemiological studies of cryptococcosis has increased since the beginning of the AIDS epidemic. Cryptococcus neoformans exists in two varieties defining four serotypes, Cryptococcus neoformans var. neoformans (serotypes A and D) and Cryptococcus neoformans var. gattii (serotypes B and C). The varieties are easy to distinguish by their differences of growth on diagnostic media. We propose here an easy serotyping method combining diagnostic media and a direct immunofluorescence assay with one monoclonal antibody (E1) specific for cryptococcal polysaccharide. The method was validated by the blinded testing of four to five reference strains of each serotype. Immunofluorescence patterns were characteristic of a given serotype provided that the variety of the strain had been defined before. For C. neoformans var. neoformans, a bright, homogeneous staining with several cell aggregates was characteristics of serotype A, whereas only a few serotype D cells were positive. For C. neoformans var. gattii, a completely negative isolate was serotype C, whereas the population of serotype B included a majority of negative cells but also included positive cells with a speckled pattern. The method was then used to serotype 156 clinical isolates from France and isolates from areas where C. neoformans var. gattii was endemic before the AIDS epidemic (13 strains from Rwanda and Zaire and 5 strains from Australia). The specificity of E1 was defined by its reactivity with various Cryptococcus spp. and analyzed according to the described cryptococcal antigenic factors. We conclude from this study that E1 provides a rapid and reliable means to serotype multiple isolates of C. neoformans.     

Effects of the two varieties of Cryptococcus neoformans cells and culture filtrate antigens on neutrophil locomotion.

Cryptococcus neoformans var. gattii (serotype B and C) isolates have a relative predilection for immunocompetent hosts, and C. neoformans var. neoformans (serotype A and D) isolates have a relative predilection for immunocompromised hosts, suggesting that normal host resistance to the former may be relatively inefficient compared with that to the latter variety. In order to assess the possibility that normal cellular host defense is inadequate in protecting against C. neoformans var. gattii, we compared the two varieties of C. neoformans cells and their culture filtrate antigens (CneF) with respect to effects on neutrophil (polymorphonuclear leukocyte [PMN]) locomotion. In a 48-well modified Boyden chamber, the cells and CneF of C. neoformans var. neoformans (serotype A and D) isolates stimulated chemotaxis and chemokinesis of human PMN and activated a complement component(s) in pooled human serum to become a chemoattractant(s) for human PMN. In contrast, the cells and CneF of C. neoformans var. gattii (serotype B and C) isolates did not stimulate chemotaxis or chemokinesis in human PMN but rather inhibited chemokinesis and chemotactic responses of PMN to pooled human serum and formylmethionyl leucyl phenylalanine. Neither of the CneF from the C. neoformans var. gattii isolates was cytotoxic to PMN. Furthermore, with the mouse model, we found that CneF from C. neoformans var. neoformans caused migration of PMN into gelatin sponges implanted in naive and immunized mice, whereas CneF from C. neoformans var. gattii inhibited PMN migration into sponges. Our results, combined with findings of others showing reduced PMN infiltration in lungs of mice infected with C. neoformans var. gattii compared with PMN infiltration in lungs of mice infected with C. neoformans var. neoformans, indicate that the relative inadequacy of normal host resistance mechanisms to prevent infection with C. neoformans var. gattii results, in part, from inhibition of PMN migration to the site of the organism.     

Molecular identification of Cryptococcus neoformans serotypes

Cryptococcus neoformans is a fungal pathogen that causes life-threatening infections primarily in immunocompromised hosts. Based on the genetic characteristics and serologic properties of capsular polysaccharides, three varieties and five serotypes have been defined: C. neoformans var. neoformans (serotype D), C. neoformans var. grubii (serotype A), hybrid serotype AD, and C. neoformans var. gattii (serotypes B and C). Epidemiologic features, such as geographic distribution and ecologic niche, and clinical characteristics have been shown to be associated with serotypes. At the present time, serotyping is based on agglutination tests with either commercial or "homemade" antisera or on immunofluorescence assays using a monoclonal antibody directed against the capsule polysaccharide. In this paper, we describe two molecular methods (PCR-restriction enzyme analysis and length polymorphism analysis) for C. neoformans serotype identification. Both are based on the sequence characteristics of a fragment of the CAP59 gene required for capsule biosynthesis. Testing of 72 C. neoformans strains including representatives of the five serotypes demonstrated the reliability of these methods.     

Sexual cycle of Cryptococcus neoformans var. grubii and virulence of congenic a and alpha isolates

Cryptococcus neoformans is a human-pathogenic fungus that has evolved into three distinct varieties that infect most prominently the central nervous system. A sexual cycle involving haploid cells of a and alpha mating types has been reported for two varieties (C. neoformans var. neoformans, serotype D, and C. neoformans var. gattii, serotypes B and C), yet the vast majority of infections involve a distinct variety (C. neoformans var. grubii, serotype A) that has been thought to be clonal and restricted to the alpha mating type. We recently identified the first serotype A isolate of the a mating type which had been thought to be extinct (strain 125.91). Here we report that this unusual strain can mate with a subset of pathogenic serotype A strains to produce a filamentous dikaryon with fused clamp connections, basidia, and viable recombinant basidiospores. One meiotic segregant mated poorly with the serotype A reference strain H99 but robustly with a crg1 mutant that lacks a regulator of G protein signaling and is hyperresponsive to mating pheromone. This meiotic segregant was used to create congenic a and alpha mating type serotype A strains. Virulence tests with rabbit and murine models of cryptococcal meningitis showed that the serotype A congenic a and alpha mating type strains had equivalent virulence in animal models, in contrast to previous studies linking the alpha mating type to increased virulence in congenic serotype D strains. Our studies highlight a role for sexual recombination in the evolution of a human fungal pathogen and provide a robust genetic platform to establish the molecular determinants of virulence.     

Decayed wood of Syzygium cumini and Ficus religiosa living trees in Delhi/New Delhi metropolitan area as natural habitat of Cryptococcus neoformans.

The isolation is reported of Cryptococcus neoformans var. gattii and C. n. var. neoformans from decayed wood inside trunk hollows of Syzygium cumini and of C. n. var. neoformans from Ficus religiosa trees in the Delhi/New Delhi metropolitan area. Fourteen of sixty-six (21%) S. cumini trees investigated proved to be positive, seven for each variety. The two varieties never co-occurred in the same hollow. C. n. var. neoformans was also isolated from three of seventeen Ficus religiosa-trees. Two of these isolates originated from decayed wood and one from bark. The C. n. var. gattii and C. n. var. neoformans isolates belonged to serotype B and serotype A, respectively. The data strongly supported colonization of S. cumini by both varieties and of F. religiosa trees by C. n. var. neoformans. Evidence of this was found by repeated isolations. For example, in 36/44 (82%) samples for C. n. var. gattii and 22/27 (81%) samples for C. n. var. neoformans, and by a high population density in the tested wood debris (maximally 6 x 10(5) colony-forming units per gram [c.f.u./g] for C. n. var. gattii and 8 x 10(4) c.f.u./g for C. n. var. neoformans). No eucalypt trees were seen near the positive S. cumini and F. religiosa trees. The densities of C. neoformans in these trees exceeded those found previously in Eucalyptus camaldulensis and in other tree species more rarely reported to be sources of C. neoformans in India. S. cumini and F. religiosa appear not to have been reported to date as sources for either C. n. var. gattii or C n. var. neoformans. Our results add to the recently emerging evidence that the natural habitat of C. n. var. gattii and C. n. var. neoformans is not specific to woody or other debris of particular tree species, but instead is more generalized.     

国内110株新生隐球菌临床株变种、基因型和交配型分析

目的 对国内部分地区的新生隐球菌(Cryptococcus neoformans)临床株进行分子流行病学调查,分析其变种、基因型和交配型的构成和分布.方法 (1)PCR指纹分型法:以野生型噬菌体M13中针对小卫星DNA的核心序列为单引物对模板进行PCR扩增,将所有受试菌株鉴定到8种主要基因型水平.(2)利用变种和交配型特异性引物扩增分型法,区分格鲁比变种(C.neoformans var.grubii)、新生变种(C.neoformans var.neoformans)和格特变种(C.neoformans var.gattii),同时鉴定α和a交配型.结果 110株临床株中,98株(89.1%)为格鲁比变种,均为VNI基因型和α交配型;9株(8.2%)格特变种,包括VGⅠ基因型、α交配型8株(7.3%)和VGⅡ基因型、α交配型1株(0.9%);2株(1.8%)为AD杂合体,VNⅢ基因型,-/α和α/-交配型各1株;1株(0.9%)为新生变种,VNⅣ基因型和a交配型.结论 我国新生隐球菌临床株包含3个变种和AD杂合体.与国外情况比较,相似的是国内临床株中绝大部分为α交配型菌株,且格鲁比变种中的VNⅠ基因型占了其中的大部分;但未发现VNⅡ、VGⅢ和VGⅣ基因型菌株.     

Diversity of DNA fingerprints in Cryptococcus neoformans.

DNA fingerprint patterns of 156 Cryptococcus neoformans isolates (26 AIDS patients, 46 non-AIDS patients, and 40 environmental sources) from both varieties (126 C. neoformans var. neoformans and 30 C. neoformans var. gattii isolates) and from seven countries were analyzed by using the DNA probe UT-4p. Nine and twelve distinct DNA fingerprint patterns were observed for isolates of the C. neoformans var. neoformans and var. gattii, respectively. No pattern was unique to AIDS patients, non-AIDS patients, or the environment. Pattern II was observed more often in non-AIDS patients (8 of 23) than in AIDS patients (0 of 25). Pattern V was the most prevalent pattern (42 of 82) in clinical and environmental isolates. Isolates from three AIDS patients in Burundi and Zaire exhibited patterns identical to each other but different from those of isolates collected from their houses (i.e., dust of floors, walls, etc.) or a nearby pigeon coop. DNA fingerprint stability was determined for 53 isolates from nine non-AIDS patients at different time intervals during 5 to 128 weeks of antifungal therapy. For eight patients, the fingerprint pattern was stable while the ninth may have had a mixed infection. Pattern II was observed in 4 of 9 patients, which is similar to 4 of 14 in other non-AIDS patients as reported here. In spite of the extensive pattern heterogeneity among 15 C. neoformans var. gattii isolates in Australia, the patterns observed in seven California isolates were quite different from those in Australia. Among isolates of C. neoformans var. gattii, one fingerprint pattern (designated b) was observed in several countries of the Far East. The fingerprint patterns of two of three environmental isolates from Eucalyptus camaldulensis trees in Australia were identical to those of 2 of the 12 clinical isolates from the country.     

High-resolution melting analysis for identification of the Cryptococcus neoformans-Cryptococcus gattii complex

We have developed a two-step method based on high-resolution melting (HRM) that reliably identifies species from the Cryptococcus species complex (Cryptococcus neoformans var. grubii, Cryptococcus neoformans var. neoformans, and Cryptococcus gattii). Our results indicate that HRM can provide a fast protocol to identify and distinguish among the main Cryptococcus species.     

Cryptococcus neoformans variety gattii.

Cryptococcus neoformans var. gattii is emerging as a primary human pathogen which is distinct genetically and biochemically from C. neoformans var. neoformans. There is increasing evidence that it should be reclassified as a separate species within the Tremellales. In nature, C. n. var. gattii has been consistently isolated from decaying wood in hollows of species of the red gum group of eucalyptus trees (Eucalyptus ser. Exsertae Blakely). The role that trees play in the life-cycle of C. n. var. gattii is not known, but its association with decaying wood is suggestive of an endophytic existence, in common with other wood-rot fungi. Despite the demonstration in the laboratory of sexual reproduction between mating types oc and a of F. neoformans var. gattii, this has not been demonstrated in nature. Human cryptococcosis develops following environmental exposure and inhalation of the infectious propagule. Whether this is the basidiospore or dessicated yeast form is uncertain. The major risk factor for development of disease appears to be exposure, though there is indirect evidence that unidentified host factors may contribute to the relatively high incidence of cryptococcosis in Australian Aboriginals. The rarity of cryptococcosis due to C. n. var. gattii in immunocompromised patients remains unexplained. Virulence determinants of C. neoformans are currently the subject of intensive investigation, especially in C. n. var. neoformans. The best-characterized, major, virulence determinants in this variety, the polysaccharide capsule, products of the laccase enzyme pathway and ability to grow at physiological temperatures, contribute to its survival in the host. They are also present in C. n. var. gattii. A potential determinant of tissue invasion, secreted phospholipase B, is produced in vitro and in vivo by C. n. var. gattii. This enzyme has now been confirmed to play a role in the virulence of C. neoformans serotype A. Disease caused by C. n. var. gattii is distinguished from that due to C. n. var. neoformans by an increased incidence of cryptococcomas in lung and brain, increased neurological morbidity and a slower response to antifungal therapy. The difference in clinical presentation is predominantly due to the effect of underlying immunocompromise in patients infected with C. n. var. neoformans.     

Isolation of Cryptococcus neoformans var. gattii from Eucalyptus camaldulensis in India.

Cryptococcus neoformans var. gattii has an ecological association with five Eucalyptus species: E. blakelyi, E. camaldulensis, E. gomphocephala, E. rudis, and E. tereticornis. After human infections due to C. neoformans var. gattii were diagnosed in the states of Punjab, Himachal Pradesh, and Karnataka, India, a study was undertaken to investigate the association of C. neoformans var. gattii with Indian eucalypts, especially in the state of Punjab. A total of 696 specimens collected from E. camaldulensis, E. citriodora and E. tereticornis (hybrid) trees were examined for the presence of C. neoformans var. gattii. Flowers from two trees of E. camaldulensis in the Chak Sarkar forest and one from the village of Periana near the Ferozepur area yielded five isolates of C. neoformans var. gattii. The origin of the trees could be traced to Australia, thus providing evidence that the distribution of E. camaldulensis correlated with the distribution of human cryptococcosis cases caused by C. neoformans var. gattii in northern India.     

Cryptococcus neoformans var. neoformans (serotype D) strains are more susceptible to heat than C. neoformans var. grubii (serotype A) strains

Cryptococcus neoformans var. neoformans (serotype D) and C. neoformans var. grubii (serotype A) differ in geographic prevalence and dermatotropism, with C. neoformans var. neoformans strains being more prevalent among isolates from temperate countries as well as from skin infections. Analysis of 19 strains from each serotype revealed wide variation in thermal susceptibility, with C. neoformans var. neoformans strains being more susceptible, on average, to heat killing. The results suggest a consistent explanation for the geographic differences between serotype A and D strains and for the dermatotropism of serotype D strains.     

Genetic characterization of environmental isolates of the Cryptococcus neoformans species complex from Brazil.

The genetic affiliation of a large number of isolates of the Cryptococcus neoformans species complex from environmental sources in Brazil has been investigated using amplified fragment length polymorphism (AFLP). The strains of C. neoformans isolated from a single tree, as well as from neighbouring trees, showed high similarity values (> 95%) of their AFLP patterns, thus suggesting considerable genetic homogeneity. The majority of isolates of C. neoformans belonged to AFLP genotype 1, and had serotype A and mating type alpha (= C. neoformans var. grubii). Three isolates belonged to AFLP genotype 2, with serotype D and mating type alpha (= C. neoformans var. neoformans). One isolate, obtained from a building in Rio de Janeiro inhabited by pigeons, belonged to the AD hybrid AFLP genotype 3. All isolates from trees of C. neoformans var. gattii (= C. gattii) belonged to AFLP genotype 6, and their banding patterns showed relatively low genetic homogeneity with a similarity value of about 76%. Isolates of this genotype occupy an environmental niche in the Americas, and they may cause disease in non-AIDS and AIDS patients as well.