Initial isolation of Candida dubliniensis from the Middle East

Prevalence of Candida dubliniensis among cancer patients in Kuwait: a 5-year retrospective study

Despite close genetic and phenotypic relationship of Candida dubliniensis with Candida albicans, its role in human disease is mostly restricted to oral colonisation, particularly among HIV-infected patients. The prevalence of C. dubliniensis in association with other disease conditions has been infrequently reported. In this study, we present data on the prevalence of C. dubliniensis among yeast species isolated from cancer patients over a 5-year period. A total of 1445 yeast isolates recovered from respiratory specimens, blood, urine and oral swabs were analysed. Candida dubliniensis isolates were provisionally identified by phenotypic methods and their identity was further confirmed by species-specific amplification and/or sequencing of internally transcribed spacer region of rDNA. Antifungal susceptibility for fluconazole was determined by Etest. The number of isolates identified as C. dubliniensis, C. albicans and other yeast species were 71 (4.9%), 862 (59.6%) and 512 (35%) respectively. All the C. dubliniensis isolates originated from respiratory (5.9%) or oral (3.2%) specimens with an overall prevalence of 4.9%, and were found to be susceptible to fluconazole. The isolation of C. dubliniensis from respiratory or oral specimens and not from blood or urine specimens suggests that this species has preference to colonise these sites of human body.

[An update on Candida dubliniensis]

Eleven years ago, Irish authors, using molecular biology, demonstrated the existence of Candida dubliniensis, a new species of Candida close to Candida albicans. Initially isolated from AIDS patients with oral candidiasis, this species was detected, even in immunocompetent patients. Recently, with new, easy to implement identification tests (latex, immunochromatography), numerous epidemiological studies were undertaken. In most studies, C. dubliniensis was most often identified in the oral cavity. In the absence of HIV infection, the proportion C. dubliniensis/C. albicans ranged from 1 to 5% but it increased to 15-20% in case of HIV infection. It should be stressed that, from an experimental point of view, the acquisition of a secondary resistance to fluconazole is more quickly obtained with C. dubliniensis that with C. albicans, this resistance remains exceptionally observed in clinical observations.

Novel 5-flucytosine-resistant clade of Candida dubliniensis from Saudi Arabia and Egypt identified by Cd25 fingerprinting

DNA fingerprinting of Candida dubliniensis isolates using the species-specific probe Cd25 previously showed that this species consists of two distinct groups, termed Cd25 group I and Cd25 group II. The present study investigated the population structure of 30 C. dubliniensis oral isolates from Saudi Arabia and Egypt using Cd25 fingerprinting and rRNA gene internal transcribed spacer region-based genotyping. Cd25 fingerprinting analysis of these isolates revealed two distinct populations, the first of which consisted of 10 closely related genotype 1 isolates (average similarity coefficient [S(AB)] value, 0.86). The second population of 20 isolates was much more heterogeneous (average S(AB) value, 0.35) and consisted of two distinct subpopulations, one of which consisted of genotype 3 isolates (n = 13) and the other of genotype 4 isolates (n = 7). A mixed dendrogram generated from the fingerprint data from the 30 Saudi Arabian and Egyptian isolates, 5 Israeli isolates, and 51 previously characterized international isolates (32 of Cd25 group I and 19 of Cd25 group II) revealed the presence of three distinct main clades. The first corresponded to the previously described Cd25 group I and contained all the Saudi Arabian, Egyptian, and Israeli genotype 1 isolates mixed with international isolates. The second clade corresponded to the previously described Cd25 group II and contained three Israeli isolates, one genotype 2 isolate, one genotype 3 isolate, and a genotype 4 variant isolate, which were mixed with international isolates. The third clade has not been described before and consisted solely of the 20 Saudi Arabian and Egyptian genotype 3 and 4 isolates identified in this study and a previously described genotype 4 Israeli isolate. All 20 Cd25 group III isolates exhibited high-level resistance to 5-flucytosine (MIC > or = 128 microg/ml), whereas all Cd25 group I and Cd25 group II isolates tested (10 Saudi Arabian and Egyptian, 16 Israeli, and 24 international) were susceptible to 5-flucytosine (MIC < or = 0.125 microg/ml). The results of this study show for the first time the presence of a novel 5-flucytosine-resistant clade of C. dubliniensis (Cd25 group III) that is predominant among isolates from Saudi Arabia and Egypt and absent from a previously characterized international collection of 98 isolates from 15 countries.

Prevalence of Candida dubliniensis among germ tube-positive Candida isolates in a maternity hospital in Kuwait

In this study, 1644 germ tube-positive Candida isolates from a maternity hospital was prospectively examined for the prevalence of Candida dubliniensis. Candida species were isolated from different clinical specimens, but majority (>90%) of them came from high vaginal swabs and urine specimens. The phenotypic and molecular identification methods for C. dubliniensis included production of rough colonies and chlamydospores on simplified sunflower seed agar, determination of assimilation profile by Vitek 2 yeast identification system, specific amplification of rDNA of internally transcribed spacer (ITS)-2 region by semi-nested PCR and direct DNA sequencing of the ITS-1 and ITS-2 regions. Three germ tube-positive Candida isolates were identified as C. dubliniensis with an overall prevalence of 0.2%. Of these, two came from urine specimens and one from a vaginal swab. None of the C. dubliniensis isolates showed resistance against fluconazole, voriconazole and amphotericin B. The study reinforces the usefulness of sunflower seed agar in presumptive identification of C. dubliniensis and confirms the prevailing view that this species forms only a minor constituent of Candida species occurring in vagina or other anatomic sites of non-HIV/AIDS-infected individuals.

Phenotypic and molecular characterization of Candida dubliniensis isolates from clinical specimens in Kuwait

OBJECTIVE

This study was carried out to characterize Candida dubliniensis using phenotypic and molecular methods and to determine the occurrence of C. dubliniensis in clinical specimens in Kuwait.

MATERIALS AND METHODS

A total of 880 clinical specimens for isolation of fungi were processed according to standard procedures. Of these, 390 germ-tube-positive clinical isolates of Candida species were examined for rough colonies with hyphal fringes and chlamydospore production on simplified sunflower seed agar for their presumptive phenotypicidentification as C. dubliniensis. The identification of C. dubliniensis isolates was further confirmed by the Vitek 2 yeast identification system, semi-nested (sn) PCR amplification of high-copy rDNA and direct DNA sequencing of the internally transcribed spacer 2 (ITS2) region.

RESULTS

Of the 390 isolates of Candida species investigated, 12 were identified as C. dubliniensis, giving an overall occurrence of 3%. All the C. dubliniensis isolates formed rough colonies with hyphal fringes and abundant chlamydospores on sunflower seed agar, did not assimilate trehalose, lactate and alpha-methyl-D-glucoside, and were isolated from human immunodeficiency virus (HIV)-negative patients. Four C. dubliniensis isolates utilized D-xylose. The species-specific primer derived from the ITS2 sequence of C. dubliniensis and used together with the panfungal reverse primer in the reamplification step of the snPCR specifically amplified rDNA from reference and clinical C. dubliniensis isolates and not from C. albicans or other Candida species. The identity of two representative isolates was confirmed by DNA sequencing of the ITS2 region.

CONCLUSIONS

The identity of 12 C. dubliniensis isolates was first established by phenotypic characteristics and then by snPCR using species-specific primers derived from ITS2 sequences. The recovery of C. dubliniensis from HIV-negative patients from Kuwait reinforces the existing view that this novel yeast species has a worldwide distribution and its occurrence is not restricted to any particular immunocompromised population.

Genotypic subgrouping of clinical isolates of Candida albicans and Candida dubliniensis by 25S intron analysis

AIMS

To determine the frequency, distribution and association of genotypes of Candida albicans and C. dubliniensis in invasive and noninvasive clinical isolates.

METHODS

Twenty-one invasive and 18 noninvasive isolates were examined by PCR amplification of a transposable intron region in the 25S rRNA gene. Isolates were genotyped following analysis of the size of resulting DNA amplicons. The isolates could be subdivided into four genotypes (A-D).

RESULTS

There was no significant difference between the frequency and genotype distribution of the invasive and noninvasive Candida isolates.

IMPACT OF THE STUDY

Therapeutic prophylaxis against candidal infections remains an area of controversy. Any diagnostic markers that reflect the potential of isolates to become invasive should be fully explored, so that more focused antifungal intervention should be targeted at these patients with these potential invasive markers. This study demonstrated that analysis of the transposable intron region in the 25S rRNA gene may be useful in helping to differentiate C. albicans from C. dubliniensis isolates, without the need for sequence analysis, which may not be readily available at primary diagnostic laboratories. However, employment of this genotypic assay is not a suitable locus to determine invasiveness and other more reliable markers of invasiveness should be sought.