[Persistence and variability of yeasts isolated from hospitalized patients: a comparison of results from Rostock and Dresden]

Changing face of Candida colonization pattern in pediatric patients with hematological malignancy during repeated hospitalizations, results of a prospective observational study (2016-2017) in shiraz, Iran

Background

Surveillance of current changes in the epidemiology of Invasive Fungal Diseases (IFDs) as an important component of the antifungal stewardship programs (ASP), requires careful regular monitoring, especially in high-risk settings such as oncology centers. This study aimed to examine Candida colonization status and corresponding current changes in children with malignancy during repeated admissions and also investigate the possible epidemiological shifts after the implementation of ASP.

Methods

In this prospective observational study, all eligible patients younger than 18 years were recruited during 2016–2017 at Amir Medical Oncology Center (AMOC) in Shiraz, Iran. Totally, 136 patients were enrolled and 482 samples were collected from different sites (oral/nasal discharges, urine and stool). Weekly regular sampling was carried out during hospitalization. Candida colonization status and epidemiological changes were monitored during repeated admissions. Samples were cultivated on Sabouraud Dextrose agar medium and identified by Polymerase Chain Reaction -Restriction Fragment Length Polymorphism (PCR-RFLP).

Results

Estimated Candida colonization incidence was 59.9% (82/136) in our patients. Candida colonization was found to be higher in oral cavity and rectum than that in nasal cavity. Among those long-term follow ups and repetitive hospitalizations, a significant number of patients exhibited changes in their colonization patterns (37.7%). Candida colonization did not reveal any significant relationship with age, sex, oncologic diseases and degree of neutropenia. C. albicans (72.0%) was found as the most common Candida species in colonized patients, followed by C. krusei, C. kefyr, C. glabrata and C. parapsilosis.

Conclusion

Given the high incidence of Candida infections in children with cancers, close monitoring of epidemiologic changes is essential for judicious management, based on local surveillance data and improvement of overall quality of care in high risk patients.

[Habitats for Candida in medical and hygienic respects]

The at present acknowledged 163 species of the genus Candida are living in different habitats. Agents of human candidosis have a comparatively restricted natural distribution, and have been discovered primarily in association with men and animals. Candida albicans holds an exceptional position opposite to the nearly 20 non-C. albicans-species with medical importance. Primary habitat is the digestive tract of men and warm-blooded animals. C. albicans is not ubiquitously distributed in the nature. Carriers of Candida may contaminate their immediate environment with yeasts, but that contamination does not usually spread far. C. albicans survives poorly on dry surfaces, a little bit longer in moist materials. Some non-C. albicans-species have their habitat also in the digestive tracts of men and animals, but different to C. albicans they are also ubiquitously distributed in the surroundings (soil, plants, foods, forages) and are much more resistant to environmental influences. The most important source of Candida species in human diseases is endogenous. The via exogen contamination arising mycoses are involved above all by non-C. albicans-species. The different habitats of the Candida species are decisive for the direct and indirect transmission of yeasts to humans and also for the preventive measures against endogenous and exogenous nosocomial Candida mycoses.

The ATP binding cassette transporter gene CgCDR1 from Candida glabrata is involved in the resistance of clinical isolates to azole antifungal agents

The resistance mechanisms to azole antifungal agents were investigated in this study with two pairs of Candida glabrata clinical isolates recovered from two separate AIDS patients. The two pairs each contained a fluconazole-susceptible isolate and a fluconazole-resistant isolate, the latter with cross-resistance to itraconazole and ketoconazole. Since the accumulation of fluconazole and of another unrelated substance, rhodamine 6G, was reduced in the azole-resistant isolates, enhanced drug efflux was considered as a possible resistance mechanism. The expression of multidrug efflux transporter genes was therefore examined in the azole-susceptible and azole-resistant yeast isolates. For this purpose, C. glabrata genes conferring resistance to azole antifungals were cloned in a Saccharomyces cerevisiae strain in which the ATP binding cassette (ABC) transporter gene PDR5 was deleted. Three different genes were recovered, and among them, only C. glabrata CDR1 (CgCDR1), a gene similar to the Candida albicans ABC transporter CDR genes, was upregulated by a factor of 5 to 8 in the azole-resistant isolates. A correlation between upregulation of this gene and azole resistance was thus established. The deletion of CgCDR1 in an azole-resistant C. glabrata clinical isolate rendered the resulting mutant (DSY1041) susceptible to azole derivatives as the azole-susceptible clinical parent, thus providing genetic evidence that a specific mechanism was involved in the azole resistance of a clinical isolate. When CgCDR1 obtained from an azole-susceptible isolate was reintroduced with the help of a centromeric vector in DSY1041, azole resistance was restored and thus suggested that a trans-acting mutation(s) could be made responsible for the increased expression of this ABC transporter gene in the azole-resistant strain. This study demonstrates for the first time the determinant role of an ABC transporter gene in the acquisition of resistance to azole antifungals by C. glabrata clinical isolates.