Genetic Differences between Avian and Human Isolates of Candida dubliniensis Brenda A. McManus, Derek J. Sullivan, Gary P. Moran, Christophe d’Enfert, Marie-Elisabeth Bougnoux, Miles A. Nunn, and David C. Coleman When Candida dubliniensis isolates obtained from seabird excrement and from humans in Ireland were com- pared by using multilocus sequence typing, 13 of 14 avian isolates were genetically distinct from human isolates. The remaining avian isolate was indistinguishable from a human isolate, suggesting that transmission may occur between humans and birds. C andida dubliniensis is an opportunistic yeast species phenotypically and genetically closely related to C. albicans, the most common cause of Candida infection. However, C. dubliniensis is less pathogenic and is most commonly associated with supericial infection in immuno- compromised persons. Although C. albicans has frequently been isolated from avian and animal sources (1–4), the re- cent study by Nunn et al. identiied C. dubliniensis from a nonhuman source (5). These isolates were obtained from the surface of Ixodes uriae ticks that lived in cracks illed with seabird excrement at 2 locations at a seabird breeding colony on Great Saltee Island off the southeastern coast of Ireland. Multilocus sequence typing (MLST) is an informative tool for investigating the population structure and epidemi- ology of many bacterial and fungal species (6). We have used MLST to show that C. dubliniensis has less genetic diversity than C. albicans and that C. dubliniensis isolates comprise 3 distinct clades (C1, C2, and C3), which cor- respond to described internally transcribed spacer (ITS) re- gion genotypes 1–4 (7). Two other research groups recently used MLST to show genetic differences between C. albi- cans isolates from humans and animals (3,4). The purpose of our study was to use MLST, the presence or absence of a previously identiied polymorphism in the CDR1 gene (8), and mating type analysis to determine genetic relatedness between avian-associated and human C. dubliniensis iso- lates and whether avian-associated isolates are a source of human opportunistic infections. The Study To obtain avian-associated C. dubliniensis isolates from a novel geographic site, fresh seabird excrement was sampled from the campus of Trinity College Dublin, ≈150 km north of Great Saltee Island by using nitrogen- gassed VI-PAK sterile swabs (Sarstedt-Drinagh, Wexford, Ireland). Samples were plated within 2 h of collection on CHROMagar Candida medium (CHROMagar, Paris, France), incubated at 30°C for 48 h, and identiied as de- scribed (7,9–12). Three new C. dubliniensis isolates were obtained from 134 fecal samples. Like isolates from Great Saltee Island (5), these 3 isolates obtained directly from freshly deposited herring gull (Larus argentatus) excre- ment were ITS genotype 1 (13). Because the isolates origi- nally described by Nunn et al. (5) were obtained from the surface of ticks living in avian excrement, avian-associated isolates refers to avian excrement–associated isolates. The avian-associated isolates were compared with 31 human C. dubliniensis strains belonging to MLST clade C1 as previ- ously reported (7), and 5 additional C. dubliniensis clade C1 human isolates from Ireland (Table). Isolates were assigned a diploid sequence type (DST) on the basis of genotype numbers for the 8 loci in the recommended C. dubliniensis MLST typing scheme (7) (Table). Six new DSTs were identiied in 13 of 14 avian- associated isolates because of the identiication of 2 new exZWF1b alleles that were found exclusively in avian- as- sociated isolates. DST2 was the only previously identiied DST (isolate AV7, Table). DST 31 was the most frequently (5/14 isolates) found DST in avian-associated C. dublinien- sis isolates, all 5 of which were from Great Saltee Island (5). Four isolates belonged to DST 27, three from Great Saltee Island and 1 from Dublin (Table). Polymorphic sites (n = 36) from the 8 MLST loci (7) of all 50 clade C1 human and avian-associated C. dubliniensis isolates were concatenated and used to construct a neigh- bor-joining tree (MEGA software program version 3.1 [14]), which included all known clade C1 DSTs identiied. Thirteen of 14 avian-associated C. dubliniensis isolates, 11 from Great Saltee Island (5) and 2 from Dublin, formed a distinct subgroup within clade C1 (Figure, panel A). This same subgroup was also identiied in trees generated by using the unweighted pair group method with arithmetic mean, maximum parsimony, and maximum likelihood, and based on related sequence types (BURST) analysis. To test Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 15, No. 9, September 2009 1467 Author afiliations: Dublin Dental School and Hospital, Dublin, Ire- land (B.A. McManus, D.J. Sullivan, G.P. Moran, D.C. Coleman); Trinity College Dublin, Dublin (B.A. McManus, D.J. Sullivan, G.P. Moran, D.C. Coleman); Institut Pasteur, Paris, France (C. d’Enfert, M.-E. Bougnoux); and National Environmental Research Council Centre for Ecology and Hydrology, Oxford, UK (M.A. Nunn) DOI: 10.3201/eid1509.081660