PCR detection of the Cryptococcus neoformans CAPS9 gene from a biopsy specimen from a case of feline cryptococcosis

Antifungal Susceptibility of Clinical Isolates and Artificially Produced Multi-azole-resistant Strains of Cryptococcus neoformans (formerly: Cryptococcus grubii) to Ravuconazole

Ravuconazole (RVCZ) is a newly available human azole drug in Japan since 2018 and is a broad-spectrum antifungal agent that exhibits excellent activity against Candida albicans and Cryptococcus neoformans (formerly: Cryptococcus grubii). The drug is also highly active against isolates that are resistant to fluconazole (FLCZ). In the present study, the in vitro susceptibility to ravuconazole (RVCZ) of Japanese clinical isolates and multi-azole-resistant strains of C. neoformans was investigated using the Clinical & Laboratory Standards Institute (CLSI) M27-A3 test. The minimum inhibitory concentrations for the 14 clinical isolates and the multi-azole-resistant strains were 0.003125-0.125 mg/L and 0.25-0.5 mg/L for RVCZ, respectively. RVCZ is as effective as ITCZ and VRCZ for treating clinical isolates from cats and humans. Moreover, RVCZ is highly effective against multi-azole-resistant strains that encode a protein with a G344S substitution in ERG11. Consequently, RVCZ has considerable potential for use as a therapeutic agent for multi-azole resistant cryptococcosis.

First Isolation of Azole-Resistant Cryptococcus neoformans from Feline Cryptococcosis

We report here, to the best of our knowledge, the first description of an in vitro fluconazole (FLZ)-resistant Cryptococcus neoformans var. grubii from a case of feline cryptococcosis. In vitro testing demonstrated that this isolate was resistant to FLZ (minimum inhibitory concentration, MIC, of 128 μg/ml) but remained susceptible to amphotericin B (0.064 µg/ml), itraconazole (0.38 µg/ml), voriconazole (0.023 µg/ml), and posaconazole (0.125 µg/ml). The predicted amino acid sequence of the lanosterol 14-α demethylase (ERG11) protein in the isolate was identical to that of the C. neoformans var. grubii reference strain, indicating that resistance was not mediated by mutation of the target gene's open reading frame. The RT-qPCR analysis for ERG11 and ATP-binding cassette (ABC) transporter-encoding gene (AFR1) indicated that the isolate increased transcription factor function of ERG11 and AFR1 than that of FLZ-susceptive strains. This observation, in combination with the lack of resistance to other azoles (that is, lack of crossresistance), suggests that resistance in our isolate was the result of overexpression of the endogenous ERG11 and ABC transporter.

Cutaneous, Subcutaneous and Systemic Mycology

The first description of dermatophytosis was recorded by Celsus, a Roman encyclopaedist who described a suppurative infection of scalp (‘porrigo’ or ‘kerion of Celsus’) in De Re Medicina (30 A.D.). Throughout the middle ages, several descriptions of dermatophytosis were produced where it is described as ‘tinea’. The keratin-destroying moths which made circular holes in the woollen garments are known as Tinea. Due to similarity in the structure of circular lesion of dermatophytosis on the smooth skin with the circular hole made by moth, Cassius Felix introduced the term ‘tinea’ to describe the lesions. In 1806, Alibert used the term ‘favus’ to describe the honey-like exudate in some scalp infections. However, the fungal aetiology of tinea was first detected by Robert Remak, a Polish physician who first observed the presence of hyphae in the crusts of favus. This detection is also a landmark in medical history because this is the first description of a microbe causing a human disease. He himself did not publish his work, but he permitted the reference of his observations in a dissertation by Xavier Hube in 1837. Remak gave all the credits of his discovery to his mentor Schoenlein who first published the fungal etiological report of favus in 1839. He observed the infectious nature of the favus by autoinoculation into his own hands and also successfully isolated the fungus later (1945) and named Achorion schoenleinii (Trichophyton schoenleinii) in honour of his mentor. In 1844, Gruby described the etiologic agent of tinea endothrix, later became known as Trichophyton tonsurans. The genus Trichophyton was created and described by Malmsten (1845) with its representative species T. tonsurans. Charles Robin identified T. mentagrophytes in 1847 and T. equinum was identified by Matruchot and Dassonville in 1898. Raymond Jacques Adrien Sabouraud (France) first compiled the description of Trichophyton in his book (Les Teignes) in 1910 which was based on his observation in artificial culture. The sexual state of dermatophyte was described by Nannizzi (1927). Emmons (1934) first reported the classification of dermatophytes based on vegetative structures and conidia. Gentles (1958) established the successful treatment of tinea capitis with griseofulvin.

Cryptococcosis in cats: ABCD guidelines on prevention and management

OVERVIEW

Cryptococcosis is worldwide the most common systemic fungal disease in cats; it is caused by the Cryptococcus neoformans- Cryptococcus gattii species complex, which includes eight genotypes and some subtypes (strains) with varying geographical distribution, pathogenicity and antimicrobial susceptibility. Cats acquire the infection from a contaminated environment. The prognosis is favourable in most cases, provided a diagnosis is obtained sufficiently early and prolonged treatment is maintained.

INFECTION

Basidiospores are the infectious propagules of Cryptococcus species as they penetrate the respiratory system and induce primary infection. Asymptomatic colonisation of the respiratory tract is more common than clinical disease. Avian guanos, particularly pigeon droppings, offer favourable conditions for the reproduction of C neoformans. Both Cryptococcus species are associated with decaying vegetation.

DISEASE SIGNS

Cryptococcosis caused by C neoformans or C gattii is indistinguishable clinically. The disease can present in nasal, central nervous system (which can derive from the nasal form or occur independently), cutaneous and systemic forms.

DIAGNOSIS

An easy and reliable test for cryptococcosis diagnosis is antigen detection in body fluids. Only isolation and polymerase chain reaction allow identification of the species genotype.

DISEASE MANAGEMENT

Amphotericin B, ketoconazole, fluconazole and itraconazole have all been used to treat cats. Surgical excision of any nodules in the skin, nasal or oral mucosa assists recovery. Continued treatment is recommended until the antigen test is negative.

PREVENTION

Efficient preventive measures have not been demonstrated. Vaccines are not available.

Molecular methods for the diagnosis and characterization of Cryptococcus: a review

Cryptococcosis is a fungal infection caused by yeasts of the genus Cryptococcus, with Cryptococcus neoformans and Cryptococcus gattii as the primary pathogenic species. This disease is a threat to immunocompromised patients, especially those who have AIDS. However, the disease has also been described in healthy individuals. The tests used to identify these microorganisms have limitations that make final diagnosis difficult. However, currently there are specific gene sequences that can be used to detect C. neoformans and C. gattii from clinical specimens and cultures. These sequences can be used for identification, typing, and the study of population genetics. Among the main identification techniques are hybridization, which was the pioneer in molecular identification and development of specific probes for pathogen detection; PCR and other PCR-based methods, particularly nested PCR and multiplex PCR; and sequencing of specific genomic regions that are amplified through PCR, which is especially useful for diagnosis of cryptococcosis caused by unconventional Cryptococcus sp. Concerning microorganism typing, the following techniques have shown the best ability to differentiate between fungal serotypes and molecular types: PCR fingerprinting, PCR-RFLP, AFLP, and MLST. Thus, the accumulation of data generated by molecular methods can have a positive impact on monitoring resistant strains and treating diseases.

Real-time polymerase chain reaction detection of Cryptococcus neoformans and Cryptococcus gattii in human samples

We report a TaqMan real-time polymerase chain reaction (PCR) protocol for diagnosing cryptococcosis. Specificity was tested with 33 fungal strains. The 7 clinical samples found positive by culture also tested positive by real-time PCR. No false negatives were found among the 94 clinical samples that were negative by culture for Cryptococcus spp. The sensitivity threshold was about 10 plasmid copies per assay.

Microreview: capsule-associated genes of Cryptococcus neoformans

Cryptococcosis, caused by Cryptococcus neoformans is a common systemic mycosis in man and animals, particularly immunocompromised patients. This pathogenic fungus produces a thick extracellular polysaccharide capsule. Four capsule-associated genes (CAP10, CAP59, CAP60, CAP64) were cloned and sequenced, and proved to be essential for capsule synthesis. However biochemical functions of CAP gene products have not been clarified yet. Recently, the relatedness of the polysaccharide capsule and four capsule-associated genes has partly been elucidated. Nucleotide sequence of four CAP gene fragments was analyzed for phylogenetic relationships, and they were in agreement with the conventional classification of varieties and serotypes within C. neoformans. Expression of four CAP genes and capsule size were examined using two media containing different amount of glucose, and the results indicated that CAP genes might play important roles in elaboration of extracellular polysaccharide capsule. Furthermore, analyses of CAP genes in various clinical samples would give the useful information to diagnose cryptococcosis in human and animals.

Fungal Diagnostics: Current Techniques and Future Trends

The diagnosis of fungal disease is a challenge that requires diligent attention to history and clinical signs as well as an astute ability to interpret laboratory data. Because fungal disease can mimic other infectious and neoplastic diseases in clinical presentation, the clinician has to be aware of fungal diseases common locally as well as in other regions of the country. A global approach to the diagnosis of fungal disease that correlates clinical signs as well as physical examination, clinical pathology, and histopathology findings with serology, culture, and the newer immunohistochemical and molecular techniques, where available, is the best approach to optimize the identification of the underlying agent.

Detection of CAP59 gene in 2 feline cases of systemic cryptococcosis

Two feline cases were diagnosed as systemic cryptococcosis due to Cryptococcus neoformans (teleomorph: Filobasidiella neoformans) by PCR assay with CAP59 gene primers using urine, serum and biopsy samples. The results of molecular analysis were consistent with the mycological findings.

Update on molecular techniques for diagnostic testing of infectious disease

The era of diagnostic molecular biology has arrived for small animal clinicians, and it is a near certainty that assays such as the PCR and RT-PCR will become more widely available for a wider array of infectious agents. Already there is an extensive list of infectious diseases of dogs and cats that have been investigated with molecular tools. A partial list is included in box 1. An understanding of the advantages and disadvantages of the molecular techniques and some of the questions these techniques can answer for clinicians can serve practitioners well in their approach to the diagnosis of infectious diseases in dogs and cats. It is likely that additional applications of these tools to small animal medicine will become apparent as investigators use and refine them for their research purposes, or as new uses emerge from human medical applications. Clinicians also are likely to reap the benefits of this knowledge. Because samples often are acquired easily from clinical patients in most practice settings, access to these tools puts all clinicians in the group of discoverers of new, or variations of, infectious diseases and their clinical manifestations.