Search

Bacterial species are associated with Candida albicans in at least 25% of patients with bloodstream infection (Candidemia). These polymicrobial infections are usually caused by coagulase-negative staphylococci, most commonly Staphylococcus epidermidis and are associated with significantly worse clinical outcomes as compared to monomicrobial infections. Here we show that bacteria are present in C. albicans cultures started from isolated single colonies. These bacteria can only be detected by the use of specific media, and prolonged incubation periods of at least 8 days. The detection of these bacteria is sensitive to the polymerase enzyme used for 16S rDNA gene amplification and is often missed in clinical laboratory analysis because of short incubation periods, media and temperatures, used in mycology clinical routine, that are unfavorable for bacterial growth. We identified bacteria in cultures of different C. albicans isolates in long-term, continuous growth by molecular analysis and microscopy. Also, we confirmed the presence of these bacteria by identification of S. epidermidis genome segments in sequencing reads of the C. albicans reference strain SC5314 genome sequencing project raw data deposited in GenBank. Our results show that the presence of associated bacteria correlates with antifungal resistance alterations observed in growth under hypoxia. Our findings reveal the intense interaction between C. albicans yeasts and bacteria and have direct implications in yeast clinical procedures, especially concerning patient treatment., (Copyright © 2018. Published by Elsevier B.V.)

The opportunistic fungal pathogen Candida albicans causes serious hematogenic hospital acquired candidiasis with worldwide impact on public health. Because of its importance as a nosocomial etiologic agent, C. albicans genome has been largely studied to identify intraspecific variation and several typing methods have been developed to distinguish closely related strains. Mitochondrial DNA can be useful for this purpose because, as compared to nuclear DNA, its higher mutational load and evolutionary rate readily reveals microvariants. Accordingly, we sequenced and assembled, with 8-fold coverage, the mitochondrial genomes of two C. albicans clinical isolates (L296 and L757) and compared these sequences with the genome sequence of reference strain SC5314. The genome alignment of 33,928 positions revealed 372 polymorphic sites being 230 in coding and 142 in non-coding regions. Three intergenic regions located between genes tRNAGly/COX1, NAD3/COB and ssurRNA/NAD4L, named IG1, IG2 and IG3, respectively, which showed high number of neutral substitutions, were amplified and sequenced from 18 clinical isolates from different locations in Latin America and 2 ATCC standard C. albicans strains. High variability of sequence and size were observed, ranging up to 56bp size difference and phylogenies based on IG1, IG2 and IG3 revealed three groups. Insertions of up to 49bp were observed exclusively in Argentinean strains relative to the other sequences which could suggest clustering by geographical polymorphism. Because of neutral evolution, high variability, easy isolation by PCR and full length sequencing these mitochondrial intergenic regions can contribute with a novel perspective in molecular studies of C. albicans isolates, complementing well established multilocus sequence typing methods., (Copyright © 2012 Elsevier B.V. All rights reserved.)

The diversity of Trypanosoma cruzi is categorized into six discrete typing units (DTUs) T. cruzi I to VI. Several studies indicate that T. cruzi I and II are ancestors of T. cruzi III-VI which are considered products of independent hybridization events. The individual haplotypes or alleles of these hybrids cluster in three groups, either closer to T. cruzi I or T. cruzi II or forming a midpoint clade between T. cruzi I and II in network phylogenies. To understand the origins of these different sets of haplotypes and test the hypothesis of a direct correlation between high entropy and positive selection, we analyzed four nuclear protein coding genes. We show that hybrid strains contain haplotypes that are mosaics probably originated by intragenic recombination. Accordingly, in phylogenies, the hybrid haplotypes are closer to one or both parentals (T. cruzi I and II) depending on the proportion of parental sequences composing the mosaics. In addition, Shannon entropy, used to measure sequence diversity, is highly correlated with positive selection in the four genes here analyzed. Our data on recombination patterns also support the hypothesis of two hybridization events in the hybrid structures of T. cruzi III-VI. Data presented and discussed here are consistent with a scenario where TcI and TcII are phylogenetically divergent forming a hybrid zone in between (T. cruzi III-VI). We predict that because of the quasi-random nature of T. cruzi I and II hybridization more DTUs, with different haplotype combinations, will be discovered in the hybrid zone., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Trypanosoma cruzi is highly diverse genetically and has been partitioned into six discrete typing units (DTUs), recently re-named T. cruzi I-VI. Although T. cruzi reproduces predominantly by binary division, accumulating evidence indicates that particular DTUs are the result of hybridization events. Two major scenarios for the origin of the hybrid lineages have been proposed. It is accepted widely that the most heterozygous TcV and TcVI DTUs are the result of genetic exchange between TcII and TcIII strains. On the other hand, the participation of a TcI parental in the current genome structure of these hybrid strains is a matter of debate. Here, sequences of the T. cruzi-specific 195-bp satellite DNA of TcI, TcII, TcIII, TcV, and TcVI strains have been used for inferring network genealogies. The resulting genealogy showed a high degree of reticulation, which is consistent with more than one event of hybridization between the Tc DTUs. The data also strongly suggest that TcIII is a hybrid with two distinct sets of satellite sequences, and that genetic exchange between TcI and TcII parentals occurred within the pedigree of the TcV and TcVI DTUs. Although satellite DNAs belong to the fast-evolving portion of eukaryotic genomes, in >100 satellite units of nine T. cruzi strains we found regions that display 100% identity. No DTU-specific consensus motifs were identified, inferring species-wide conservation., (Copyright 2010 Elsevier B.V. All rights reserved.)