Candida dubliniensis…

A Troublesome

irst described in 1995 flora in a small percentage of and discovered healthy persons. amongst AIDS patients Fin Dublin, Ireland; The role of C. dubliniensis as dubliniensis has been a pathogen was once thought a troublesome organism for to be limited to oral microbiologists for several candidiasis; however more reasons. serious cases of septicemia have been reported. First of all, the phenotypic tests for C. dubliniensis can be, at times, unreliable Macroscopic Morphology Jay Hardy, CLS, SM (ASCP) leading to its erroneous identification as C. albicans. Colonies on Sabouraud’s dextrose agar at 25°C are

Jay Hardy is the founder and Secondly, this organism has white to cream, soft, and CEO of Hardy Diagnostics. been known to develop smooth to wrinkled; and are He began his career in resistance upon exposure to indistinguishable from C. microbiology as a Medical the common anti-fungal, albicans. Colonies grown on Technologist in Santa , leading to chromogenic Candida agar are Barbara, California. treatment failures. dark green as opposed to the In 1980, he began light blue-green exhibited by manufacturing culture media Although C. albicans. for the local hospitals. remains the most common Today, Hardy Diagnostics is opportunistic yeast pathogen the third largest media manufacturer in the U.S. in patients with AIDS and Microscopic Morphology other immunocompromised To ensure rapid and reliable persons, species less On cornmeal following 72 turn around time, Hardy susceptible to fluconazole, hours incubation at 25°C, Diagnostics maintains six such as C. dubliniensis, are abundant branched distribution centers, and produces over 2,700 becoming more common. pseudohyphae and true products used in clinical and hyphae with blastoconidia are industrial microbiology C. dubliniensis is most often present. Many strains produce laboratories throughout the found in oropharyngeal an abundance of world. lesions of AIDS patients. resulting in However the organism can be excess of 25-30 being considered indigenous oral observed in each microscopic field. Growth at 42 degrees C the oral cavity of AIDS patients. This organism grows very poorly or not at all at 42 degrees C. Unfortunately, a Antifungal Susceptibility small percentage of C. albicans isolates will also The most important problem have difficultly growing at with C. dubliniensis is its this higher temperature. apparent ability to become resistant to Fluconazole upon repeated exposure to this Prevalence and drug, as seen in patients on Epidemiology long term therapy. arrangement is usually seen in pairs, Candida dubliniensis is found Although most strains are chains, and clusters (as all around the world. It is sensitive, Fluconazole appears opposed to C. albicans thought to have been to be less active against C. chlamydospores, which previously identified as dubliniensis than against C. usually occur singly). Candida albicans and has albicans, since C. dubliniensis been recognized as a distinct is usually associated with species since 1995. recurrent episodes of Germ Tubes candidiasis and protracted exposure to azole antifungal C. dubliniensis is germ tube drugs in patients with AIDS. positive which accounts for its historic miss-identification as For this reason, the control of C. albicans. C. dubliniensis may require

higher doses of Fluconazole or the use of other anti-fungal The organism has been found agents. in the stool, urine, vagina, and oral cavity of healthy individuals; although it is most commonly seen in immunocompromised patients. Various studies report a prevalence of C. dubliniensis of 15 to 30% in

Laboratory Identification

Test C. albicans C. dubliniensis Germ tube Positive Positive Chlamydospores Positive (usually single) Positive (usually in pairs and clusters) Growth at 42 deg. C (note: one Mostly Positive Negative or slight growth study reports better results at 45 deg. C) d-Xylose assimilation Mostly Positive Mostly Negative Trehalose assimilation (not Positive Mostly Negative rapid) Methyl-D-Glucosidase (MDG) Mostly Positive Negative Chromogenic media Blue green colonies Dark green colonies (however this characteristic is usually lost upon subculture) Bird Seed Agar (Staib Agar, Smooth colonies Rough colonies, with fringe or Niger seed agar, Caffeic Acid “feet” Agar) Casein Agar (24 deg. C, at 48 No Chlamydospore Abundant Chlamydospore hours) production production

As you can see, this troublesome organism does not always play by the rules and requires some special consideration by microbiologists who are attempting to identify the agent of disease and predict the best treatment option.

Jay Hardy, CLS, SM (ASCP) Santa Maria, CA