Persistent Candida albicans colonization and molecular mechanisms of azole resistance in autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) patients.
OBJECTIVE
Patients with autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED, APS-I) suffer from chronic candidosis caused mainly by Candida albicans, and repeated courses of azole antifungals have led to the development of resistance in the APECED patient population in Finland. The aim of our study was to address whether the patients are persistently colonized with the same or genetically closely related strains, whether epidemic strains are present and which molecular mechanisms account for azole resistance.


METHODS
Sets of C. albicans (n = 19) isolates from nine APECED patients reported with decreased susceptibility to fluconazole isolated up to 9 years apart were included. The strains were typed by multilocus sequence typing. CDR1/2, MDR1 and ERG11 mRNA expression was analysed by northern blotting and Cdr1, Cdr2 and Mdr1 protein expression by western blotting, and TAC1 and ERG11 genes were sequenced.


RESULTS
All seven patients with multiple C. albicans isolates analysed were persistently colonized with the same or a genetically closely related strain for a mean of 5 years. All patients were colonized with different strains and no epidemic strains were found. The major molecular mechanisms behind the azole resistance were mutations in TAC1 contributing to overexpression of CDR1 and CDR2. Six new TAC1 mutations were found, one of which (N740S) is likely to be a gain-of-function mutation. Most isolates were found to have gained multiple TAC1 and ERG11 point mutations.


CONCLUSIONS
Despite clinically successful treatment leading to relief of symptoms, colonization by C. albicans strains is persistent within APECED patients. Microevolution and point mutations occur within strains, leading to the development of azole-resistant isolates.
Siikala
Emilia
E
Department of Bacteriology and Immunology, Haartman Institute, University of Helsinki, Helsinki, Finland. emilia.siikala@helsinki.fi
Rautemaa
Riina
R
Richardson
Malcolm
M
Saxen
Harri
H
Bowyer
Paul
P
Sanglard
Dominique
D
D000935:Antifungal Agents / Q000494:pharmacology* / Q000627:therapeutic use; D001393:Azoles / Q000494:pharmacology* / Q000627:therapeutic use; D002176:Candida albicans / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D002180:Candidiasis, Oral / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology*; D002908:Chronic Disease; D025141:Drug Resistance, Fungal / Q000235:genetics*; D005387:Finland / Q000453:epidemiology; D015725:Fluconazole / Q000494:pharmacology / Q000627:therapeutic use; D005656:Fungal Proteins / Q000235:genetics; D006801:Humans; D026901:Membrane Transport Proteins / Q000235:genetics; D008826:Microbial Sensitivity Tests; D009154:Mutation; D016884:Polyendocrinopathies, Autoimmune / Q000150:complications* / Q000453:epidemiology / Q000382:microbiology
D000935:Antifungal Agents; D001393:Azoles; C094693:CDR1 protein, Candida albicans; D005656:Fungal Proteins; D026901:Membrane Transport Proteins; D015725:Fluconazole