A rapid urease test for presumptive identification of Cryptococcus neoformans

Canteros, Cristina Elena; Rodero, L; Rivas, María Cristina; Davel, Graciela

doi:10.1007/bf00436656

Cited by 13 publications

(5 citation statements)

References 11 publications

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“…Plates for urease test were prepared with Christensen's urea agar, and 5 × 10 4 cells were spotted in the center of the plate. Cells were cultivated for 120 h and assessed by difference represented by the pink color of the colony and the size of the pink halo (81, 82).…”

Section: Methodsmentioning

confidence: 99%

Cryptococcus neoformansGlucuronoxylomannan and Sterylglucoside Are Required for Host Protection in an Animal Vaccination Model

Colombo

Rella

Normile

et al. 2019

mBio

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Cryptococcus neoformans is an encapsulated fungal pathogen that causes meningoencephalitis. There are no prophylactic tools for cryptococcosis. Previously, our group showed that a C. neoformans mutant lacking the gene encoding sterylglucosidase (Δsgl1) induced protection in both immunocompetent and immunocompromised murine models of cryptococcosis. Since sterylglucosidase catalyzes degradation of sterylglucosides (SGs), accumulation of this glycolipid could be responsible for protective immunity. In this study, we analyzed whether the activity of SGs is sufficient for the protective effect induced by the Δsgl1 strain. We observed that the accumulation of SGs impacted several properties of the main polysaccharide that composes the fungal capsule, glucuronoxylomannan (GXM). We therefore used genetic manipulation to delete the SGL1 gene in the acapsular mutant Δcap59 to generate a double mutant (strain Δcap59/Δsgl1) that was shown to be nonpathogenic and cleared from the lung of mice within 7 days post-intranasal infection. The inflammatory immune response triggered by the Δcap59/Δsgl1 mutant in the lung differed from the response seen with the other strains. The double mutant did not induce protection in a vaccination model, suggesting that SG-related protection requires the main capsular polysaccharide. Finally, GXM-containing extracellular vesicles (EVs) enriched in SGs delayed the acute lethality of Galleria mellonella against C. neoformans infection. These studies highlighted a key role for GXM and SGs in inducing protection against a secondary cryptococcal infection, and, since EVs notoriously contain GXM, these results suggest the potential use of Δsgl1 EVs as a vaccination strategy for cryptococcosis. IMPORTANCE The number of deaths from cryptococcal meningitis is around 180,000 per year. The disease is the second leading cause of mortality among individuals with AIDS. Antifungal treatment is costly and associated with adverse effects and resistance, evidencing the urgency of development of both therapeutic and prophylactic tools. Here we demonstrate the key roles of polysaccharide- and glycolipid-containing structures in a vaccination model to prevent cryptococcosis.

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Section: Methodsmentioning

confidence: 99%

Cryptococcus neoformansGlucuronoxylomannan and Sterylglucoside Are Required for Host Protection in an Animal Vaccination Model

Colombo

Rella

Normile

et al. 2019

mBio

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“…Although there have been some rare case reports of urease-negative C. neoformans strains causing human infection (2,29), the vast majority of clinical isolates produce large amounts of urease. In fact, the rapid detection of urease activity is one means of tentatively identifying C. neoformans from clinical specimens (3,36). It is likely that the primary role of this enzyme for C. neoformans is to convert urea to a usable nitrogen source in its ecological niche.…”

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confidence: 99%

Urease as a Virulence Factor in Experimental Cryptococcosis

et al. 2000

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Urease catalyzes the hydrolysis of urea to ammonia and carbamate and has been found to be an important pathogenic factor for certain bacteria. Cryptococcus neoformans is a significant human pathogenic fungus that produces large amounts of urease; thus we wanted to investigate the importance of urease in the pathogenesis of cryptococcosis. We cloned and sequenced the genomic locus containing the single-copy C. neoformans urease gene (URE1) and used this to disrupt the native URE1 in the serotype A strain H99. The ure1 mutant strains were found to have in vitro growth characteristics, phenoloxidase activity, and capsule size similar to those of the wild type. Comparison of a ure1 mutant with H99 after intracisternal inoculation into corticosteroid-treated rabbits revealed no significant differences in colony counts recovered from the cerebrospinal fluid. However, when these two strains were compared in both the murine intravenous and inhalational infection models, there were significant differences in survival. Mice infected with a ure1 strain lived longer than mice infected with H99 in both models. The ure1 strain was restored to urease positivity by complementation with URE1, and two resulting transformants were significantly more pathogenic than the ure1 strain. Our results suggest that urease activity is involved in the pathogenesis of cryptococcosis but that the importance may be species and/or infection site specific.Urease is a metalloenzyme that catalyzes the hydrolysis of urea to ammonia and carbamate. Under physiological conditions, this reaction can result in an increase in pH. Urease activity has been found in several bacteria, fungi, and plants and has been shown to be an important pathogenic factor for the bacteria Helicobacter pylori and Proteus mirabilis (12,14,33). H. pylori is the major cause of peptic ulcer disease in humans, and urease is essential for pathogenesis in experimental models. Urease-negative strains of H. pylori constructed using a variety of molecular and genetic techniques were unable to infect gastric mucosa (12,33). It has been postulated that the hydrolysis of urea and the resulting increase in pH allow H. pylori to survive within the gastric mucosa. It has also been postulated that much of the tissue damage induced by this organism is a result of ammonium hydroxide produced through the actions of urease (22,23), and there are data that the actions of urease may alter the function of white blood cells (18)(19)(20). Because of the importance of this enzyme in the pathogenesis of peptic ulcer disease, urease inhibitors and urease vaccines are currently being developed for clinical use.Many fungi pathogenic to humans have urease activity, among which are Cryptococcus neoformans, Coccidioides immitis, Histoplasma capsulatum, Sporothrix schenckii, and species of Trichosporon and Aspergillus. The first urease gene cloned from a human pathogenic fungus was that of C. immitis (35). The coccidioidal urease gene has been shown to be expressed in vivo, and there are suggestions that it p...

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“…Urease‐negative C. neoformans strains that cause human infection have been rarely reported , although the vast majority of clinical isolates produce large amounts of urease. In fact, rapid detection of urease activity is one means of tentatively identifying C. neoformans in clinical specimens . In the C. neoformans infection model of Olszewski et al.…”

Section: Discussionmentioning

confidence: 99%

Transcriptomic and virulence factors analyses of Cryptococcus neoformans hypoxia response

Kong

Yang

Wang

et al. 2017

APMIS

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Cryptococcus neoformans is an environmental pathogen requiring atmospheric levels of oxygen for optimal growth. Upon inhalation, C. neoformans disseminates to the brain and causes meningoencephalitis. However, the mechanisms by which the pathogen adapts to the low-oxygen environment in the brain have not been investigated. We isolated a C. neoformans strain with a small capsule from a host tissue, although this strain produces large capsules in normoxic conditions. We hypothesize that this difference in capsule size is attributed to hypoxia caused by chronic inflammatory response. This study investigated the effect of hypoxia on virulence factors (including capsule, melanin, urease, and phospholipase) of C. neoformans and conducted transcriptomic analyses of the virulence-associated genes. We found that C. neoformans grew under hypoxic condition, albeit slowly, and that hypoxia may have inhibited the capsule size, melanin production, and phospholipase and urease activities in C. neoformans.

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A rapid urease test for presumptive identification of Cryptococcus neoformans

Cited by 13 publications

References 11 publications

Cryptococcus neoformansGlucuronoxylomannan and Sterylglucoside Are Required for Host Protection in an Animal Vaccination Model

Cryptococcus neoformansGlucuronoxylomannan and Sterylglucoside Are Required for Host Protection in an Animal Vaccination Model

Urease as a Virulence Factor in Experimental Cryptococcosis

Transcriptomic and virulence factors analyses of Cryptococcus neoformans hypoxia response

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