Hypertonic sabouraud dextrose agar as a substrate for differentiation of Candida dubliniensis

Analyzing the quality differences between healthy and moldy cigar tobacco leaves during the air-curing process through fungal communities and physicochemical components

Introduction

The air-curing process of cigar tobacco, as a key step in enhancing the quality of cigars, is often susceptible to contamination by mold spores, which severely constrains the quality of cigar tobacco.

Methods

This study employed high-throughput Illumina sequencing technology and a continuous flow analysis system to analyze the differences between the microbial communities and physicochemical components of moldy and healthy cigar tobacco leaves. Furthermore, correlation analysis was performed to reveal the impact of mold on the quality of cigar tobacco.

Results

The differences between the microbial flora and physicochemical compositions of moldy (MC) and healthy (HC) tobacco leaves were analyzed, revealing significant disparities between the two groups. Aspergillus spp. represented the dominant mold in MC, with nine out of twelve isolated molds showing higher quantities on MC than on HC. Mold contamination notably decreased the total nitrogen (TN), total phosphorus (TP), total alkaloids (TA), starch, protein, and flavor constituents while increasing the total fatty acid esters (TFAA), which was accompanied by a shift towards weakly acidic pH in the leaves. Fungal community analysis indicated a significant reduction in the fungal operational taxonomic unit (OUT) numbers and diversity indices in MC, contrasting with the bacterial trends. Aspergillus exhibited significantly higher relative abundance in MC, with LEfSe analysis pinpointing it as the primary driver of differentiation. Furthermore, significant negative correlations were observed between Aspergillus and TP, starch, TA, and protein, while a significant positive association was evident with TFAA. Network analysis underscored the pivotal role of Aspergillus as the species influencing disparities between HC and MC, with its abundance serving as a critical determinant during the air-curing process.

Discussion

This study elucidated substantial quality distinctions between MC and HC during air-curing, with Aspergillus emerging as the key species contributing to leaf mold.

Evaluation of various phenotypic methods for differentiation of Candida dubliniensis from Candida albicans

INTRODUCTION

Candida dubliniensis was first identified by Sullivan et al. (1995) in Dublin, Ireland. Its clinical significance is associated with development of fluconazole-resistance and invasive diseases in immunocompromised hosts. C. dubliniensis share many features with C. albicans so has been overlooked and misidentified for a long time.

AIMS

Evaluation of various phenotypic tests with polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) as a gold standard to find out the best method/methods for identifying C. dubliniensis.

MATERIALS AND METHODS

First PCR-RFLP was performed on 186C. albicans and 14C. dubliniensis strains and then five phenotypic tests were performed simultaneously on all the strains.

RESULTS

The results of salt tolerance test at 48 h, colony color on HiCrome candida differential agar (HCDA) at 72 h, heat tolerance test at 48 h, xylose assimilation using discs at 72 h and growth on xylose based agar medium (XAM) at 48 h are completely concordant with PCR-RFLP. Colony color on Tobacco agar could differentiate accurately 100% test strains while peripheral hyphal fringes and chlamydosporulation on this agar was seen in only 86% and 87% respectively. Our routine methods proved to be cost effective than PCR-RFLP but the turnaround time was same or more than PCR-RFLP.

CONCLUSION

For routine identification of C. dubliniensis we recommend use of colony color on HCDA and growth on XAM as simple, reliable and inexpensive method.

Oral yeast colonization in patients with eating disorders: commensal acquisition or due to purgative habits?

Oral problems are common in patients diagnosed with Eating Disorders (ED) and still require better elucidation. We aimed to analyze the prevalence of oral Candida spp in individuals with ED. The sample of the study was comprised of 30 women with purgative habits and 15 without purgative habits. Samples of the oral cavity were collected by sterile cotton swab rubbed on soft tissues and teeth. Yeasts were isolated on Sabouraud dextrose agar. Yeasts were isolated from the oral cavity of 53% of the patients yielding 75 yeast isolates; of these, 43 were identified by conventional mycological methods: C. parapsilosis (n=19), C. glabrata (n=16), Rhodotorula sp (n= 6), C. famata (n=2). The remaining 32 isolates were presumptively identified as C. albicans or C. dubliniensis and required mass spectrometry for the final differentiation: 28 isolates were confirmed as C. albicans and four as C. dubliniensis. Among the control group, only four subjects (26.7%) were found to harbor C. albicans. The four C. dubliniensis isolates were from two patients, one that was only colonized and the other, with severe ED, was diagnosed with an oral candidiasis as demonstrated by the presence of pseudohyphae on the direct mycological exam from different sites. The increased rate of isolation of non-albicans species, such as C. glabrata, C. parapsilosis, and C. dubliniensis in the oral cavity from ED patients with nutritional deficiency may suggest that purgative habits of these patients can lead to changes in normal flora and predispose to oral candidiasis.

Cytokine gene polymorphism in denture stomatitis patients: A clinical study

OBJECTIVE

This clinical study investigated the association between cytokine gene polymorphism and Candida growth in denture stomatitis (DS) patients.

SUBJECTS AND METHODS

Saliva and blood samples of 160 complete denture wearers (80 healthy controls and 80 with DS) were collected for mycological and gene polymorphism testing, respectively. Salivary Candida growth and TNF-α, TGF-β, IL-6, and IL-10 genotypes were investigated. Data were analyzed using Student's t test, Mann-Whitney U test, chi-square analysis, and continuity (yates) correction tests (p < .05).

RESULTS

Candida albicans colony counts in saliva were significantly higher in the DS group and in the TNF-α GG genotype (p < .05). TGF-β TC GG and TGF-β CC GG haplotypes were significantly higher in DS and control groups, respectively (p < .05). C. albicans colony counts were significantly higher in control group in the TGF-β TC GG haplotype (p < .05). Candida glabrata colony counts were significantly higher in the DS group than the control group in IL-6 GG genotype (p < .05). The difference between DS types in IL-6 genotypes was significant with lower expression level in DS type 3 than DS type 1 and also type 2 (p ≤ .01).

CONCLUSION

The significant differences in some genotypes of the TNF-α, TGF-β, and IL-6 in DS patients are promising in understanding the host defense in DS.

Hypertonic xylose agar medium: A novel medium for differentiation of Candida dubliniensis from Candida albicans

BACKGROUND

Candida dubliniensis is a pathogenic Candida species which shares many phenotypic features with Candida albicans. These similarities have caused significant problems in the identification of C. dubliniensis in an average clinical mycology laboratory. Several phenotypic-based tests have been developed to distinguish C. albicans from C. dubliniensis but none has been demonstrated being sufficient alone for accurate differentiation of the two species.

AIM

To facilitate the differentiation of these species, we evaluated the utility of a novel medium 'Hypertonic Xylose Agar Medium' (HXAM).

MATERIALS AND METHODS

A total of 200 Candida spp. were tested in this study which included 186 stock strains of C. albicans and 14 strains of C. dubliniensis. Identification of all these strains was confirmed by polymerase chain reaction-restriction fragment length polymorphism using Bln I (Avr II) enzyme. All isolates were inoculated on HXAM, incubated at 28°C and examined for visible growth every day up to 7 days.

RESULTS

On this medium at 28°C, all 186 C. albicans isolates showed visible growth at 48 h of incubation whereas none of the 14 C. dubliniensis isolates did so even on extending the incubation period up to 7 days.

CONCLUSION

Hence, we propose HXAM as a sole phenotypic method for identifying C. dubliniensis from germ-tube-positive isolates or from stock collections of known C. albicans.

Paediatric oropharyngeal and cutaneous candidiasis with special reference to Candida dubliniensis

Mucocutaneous and cutaneous candidiasis, though common in children, is often under-reported. The prevalence of Candida dubliniensis in causing these infections in this age group is also largely unknown. A prospective epidemiological cross-sectional study for candidiasis was performed in paediatric patients clinically suspected of candidiasis with oropharyngeal lesions (75 patients), cutaneous lesions (18 patients) and lesions at both sites (2 patients). Candida species were identified by conventional tests. For C. dubliniensis, chlamydospore production, growth on tobacco agar and growth at 45 °C were performed. Nine isolates were confirmed at a reference centre. The rates of candidiasis were 77.3 % (58 out of 75 patients clinically suspected of candidiasis) and 83.3 % (15/18) in oropharyngeal and cutaneous lesions respectively, and 1 of the 2 children with lesions at both sites was diagnosed as having chronic mucocutaneous candidiasis due to C. dubliniensis. The commonest species isolated was Candida albicans, in 41 (70.7 %) patients with oropharyngeal candidiasis and 11 (73.3 %) with cutaneous lesions; C. dubliniensis was isolated from 11 and 3 children respectively. In the paediatric population, C. albicans predominates in mucocutaneous and cutaneous candidiasis, with C. dubliniensis also contributing substantially.

The usefulness of DNA sequencing after extraction by Whatman FTA filter matrix technology and phenotypic tests for differentiation of Candida albicans and Candida dubliniensis

Since C. dubliniensis is similar to C. albicans phenotypically, it can be misidentified as C. albicans. We aimed to investigate the prevalence of C. dubliniensis among isolates previously identified as C. albicans in our stocks and to compare the phenotypic methods and DNA sequencing of D1/D2 region on the ribosomal large subunit (rLSU) gene. A total of 850 isolates included in this study. Phenotypic identification was performed based on germ tube formation, chlamydospore production, colony colors on chromogenic agar, inability of growth at 45 °C and growth on hypertonic Sabouraud dextrose agar. Eighty isolates compatible with C. dubliniensis by at least one phenotypic test were included in the sequence analysis. Nested PCR amplification of D1/D2 region of the rLSU gene was performed after the fungal DNA extraction by Whatman FTA filter paper technology. The sequencing analysis of PCR products carried out by an automated capillary gel electrophoresis device. The rate of C. dubliniensis was 2.35 % (n = 20) among isolates previously described as C. albicans. Consequently, none of the phenotypic tests provided satisfactory performance alone in our study, and molecular methods required special equipment and high cost. Thus, at least two phenotypic methods can be used for identification of C. dubliniensis, and molecular methods can be used for confirmation.

Frequency of fungi in respiratory samples from Turkish cystic fibrosis patients

An increased isolation of fungi from the respiratory tract of patients with cystic fibrosis (CF) has been reported. The prevalence of different fungi in CF patients from Turkey is not known. Our aim was to determine the frequency of fungi in the respiratory tract of Turkish CF patients. We investigated a total of 184 samples from 48 patients. Samples were inoculated on Medium B+ and CHROMagar Candida. Candida albicans was the predominant yeast isolated [30 patients (62.5%)], followed by C. parapsilosis [6 (12.5%)] and C. dubliniensis 5 (10.4%). Aspergillus fumigatus was the most common filamentous fungus [5 (10.4%)] and non-fumigatus Aspergillus species were isolated from four (8.3%) patients. Staphylococcus aureus was the most frequently detected bacterium in C. albicans positive samples (53.57%). A. fumigatus and Pseudomonas aeruginosa or S. aureus were detected together in 75% of A. fumigatus positive samples each. No statistically significant relationship was detected between growth of yeast and moulds and age, gender, the use of inhaled corticosteroids or tobramycin. No significant correlation was found between the isolation of C. albicans, A. fumigatus and P. aeruginosa, Stenotrophomonas maltophilia or S. aureus, and the isolation of C. albicans and Haemophilus influenzae. Other factors which may be responsible for the increased isolation of fungi in CF need to be investigated.

A simple and reliable PCR-restriction fragment length polymorphism assay to identify Candida albicans and its closely related Candida dubliniensis

Candida dubliniensis is an emerging pathogen capable of causing superficial as well as systemic infections. Due to its close similarity to C. albcians, conventional methods based on phenotypic traits are not always reliable in identification of C. dubliniensis. In this study, we developed a PCR-restriction fragment length polymorphism (RFLP) assay to identify and discriminate between the two closely related species. The D1/D2 region of 28S rDNA was amplified by PCR and enzymatically digested by ApaI and BsiEI respectively. PCR products of both species were digested into two fragments by ApaI, but those of other yeast species were undigested. BsiEI cut the PCR products of C. albicans into two fragments but not those of C. dubliniensis. Thus two species were differentiated. We evaluated 10 reference strains representing 10 yeast species, among which C. albicans and C. dubliniensis were successfully identified. A total of 56 phenotypically characterized clinical isolates (42 C. albicans isolates and 14 C. dubliniensis isolates) were also investigated for intra-species variability. All tested isolates produced identical RFLP patterns to their respective reference strains except one initially misidentified isolate. Our method offers a simple, rapid and reliable molecular method for the identification of C. albicans and C. dubliniensis.

First isolation of Candida dubliniensis from oral cavities of dermatological patients in Nanjing, China

Candida dubliniensis is an emerging pathogen capable of causing both superficial and systemic infections. Although C. dubliniensis and C. albicans are phenotypically similar, the two species differ in terms of epidemiology and the ability to rapidly develop resistance to fluconazole. C. dubliniensis is primarily associated with oral candidiasis of human immunodeficiency virus (HIV)-infected individuals. In this study, we describe the first recovery of C. dubliniensis from oral cavities of non-HIV-infected patients with dermatological diseases in Nanjing, China. The isolates were phenotypically characterized as C. dubliniensis by their production of brown rough colonies and chlamydospores on tobacco agar and their inability to grow on hypertonic Sabouraud dextrose agar or to assimilate xylose or α-methyl-D-glycoside. The species identification was subsequently confirmed by amplification and sequencing of the internal transcribed spacer region (ITS). Three C. dubliniensis isolates out of 128 (2.3%) presumptive C. albicans/C. dubliniensis ones were finally identified. Further sequence analysis separated the three isolates into two of the four reported ITS genotypes. Antifungal susceptibility testing showed that they were susceptible to fluconazole, itraconazole, voriconazole, micafungin, and amphotericin B. This study adds to the accumulating evidence that C. dubliniensis is widely distributed in non-HIV-infected populations worldwide.

Differentiation between Candida albicans and Candida dubliniensis using hypertonic Sabouraud broth and tobacco agar

INTRODUCTION

Opportunistic fungal infections in immunocompromised hosts are caused by Candida species, and the majority of such infections are due to Candida albicans. However, the emerging pathogen Candida dubliniensis demonstrates several phenotypic characteristics in common with C. albicans, such as production of germ tubes and chlamydospores, calling attention to the development of stable resistance to fluconazole in vitro. The aim of this study was to evaluate the performance of biochemistry identification in the differentiating between C. albicans and C. dubliniensis, by phenotyping of yeast identified as C. albicans.

METHODS

Seventy-nine isolates identified as C. albicans by the API system ID 32C were grown on Sabouraud dextrose agar at 30°C for 24-48h and then inoculated on hypertonic Sabouraud broth and tobacco agar.

RESULTS

Our results showed that 17 (21.5%) isolates were growth-inhibited on hypertonic Sabouraud broth, a phenotypic trait inconsistent with C. albicans in this medium. However, the results observed on tobacco agar showed that only 9 (11.4%) of the growth-inhibited isolates produced characteristic colonies of C. dubliniensis (rough colonies, yellowish-brown with abundant fragments of hyphae and chlamydospores).

CONCLUSIONS

The results suggest that this method is a simple tool for screening C. albicans and non-albicans yeast and for verification of automated identification.

Application of hypertonic Sabouraud glucose agar for differentiation of Candida dubliniensis from Candida albicans

An evaluation of hypertonic Sabouraud glucose agar (SGA) with 6.5% NaCl for phenotypic differentiation of Candida dubliniensis from Candida albicans is reported. Identity of the test fungi (C. albicans, 84; C. dubliniensis, 18) was based on their typical phenotypic characteristics and confirmed by a diagnostic polymerase chain reaction that targets the novel C. dubliniensis group I intron in the large ribosomal subunit. At 96 h of incubation at 28 °C, all of the 84 C. albicans isolates showed growth on hypertonic SGA contrary to the consistently negative results with the 20 C. dubliniensis isolates. In strong contrast, chlamydospore formation on Staib agar yielded 10 (11.9%) false-positive results and 74 (88%) of the test C. albicans isolates showed false-negative results at 45 °C. We conclude that hypertonic SGA with 6.5% NaCl can be recommended for wider application as a reliable and inexpensive medium for routine differentiation of C. dubliniensis from C. albicans.

Differences in exoenzyme production and adherence ability of Candida spp. isolates from catheter, blood and oral cavity

Phospholipase and proteinase production and the ability of adhesion to buccal epithelial cells (BEC) of 112 Candida isolates originated from oral cavity of HIV infected patients and from blood and catheter of intensive care unit patients were investigated. The proteinase production was detected by inoculation into bovine serum albumin (BSA) agar and the phospholipase activity was performed using egg yolk emulsion. A yeast suspension of each test strain was incubated with buccal epithelial cells and the number of adherence yeast to epithelial cells was counted. A percentage of 88.1% and 55.9% of Candida albicans and 69.8% and 37.7% of non-albicans Candida isolates produced proteinase and phospholipase, respectively. Non-albicans Candida isolated from catheter were more proteolytic than C. albicans isolates. Blood isolates were more proteolytic than catheter and oral cavity isolates while oral cavity isolates produced more phospholipase than those from blood and catheter. C. albicans isolates from oral cavity and from catheter were more adherent to BEC than non-albicans Candida isolates, but the adhesion was not different among the three sources analyzed. The results indicated differences in the production of phospholipase and proteinase and in the ability of adhesion to BEC among Candida spp. isolates from different sources. This study suggests that the pathogenicity of Candida can be correlated with the infected site.