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New species of yeast found in patients with HIV (5/20/98)

A new species of yeast, never before identified in the United States, has been found in oral samples from patients in Texas who are infected with the human immunodeficiency virus (HIV).

William R. Kirkpatrick and his colleagues, from the department of medicine at The University of Texas Health Science Center at San Antonio, have announced that the yeast, Candida dubliniensis, was found in oral samples from 17 percent of HIV-infected patients participating in his study group. Although the new-found yeast, associated with oral fungal infection, has been found in various geographical regions throughout the world, this is the first time Candida dubliniensis has been isolated in American patients.

The findings were presented in Atlanta on May 20 at the 98th General Meeting of the American Society for Microbiology.

The researchers suggest that in former studies some yeast isolates may have been mis-identified as the most common oral yeast isolate, Candida albicans, rather than the new species. Given the similarities between C. albicans and C. dubliniensis, proper identification has been difficult.

Patients infected with HIV who have been receiving care at the Health Science Center and at the South Texas Veterans Health Care System were enrolled in a longitudinal study of oral thrush. Oral cultures obtained from these patients were periodically studied in the laboratory of Thomas F. Patterson, MD, from the department of medicine, division of infectious diseases at the Health Science Center. In this study, 23 C. dubliniensis isolates were identified from 48 atypical yeast isolates using an atypical color pattern on a chromogenic (capable of converting into a pigment or dye) medium called CHROMagar Candida, which was the key in the subsequent identification of these yeasts. Overall, C. dubliniensis was identified in 17 percent (or 11 out of 63) of the advanced AIDS patients serially evaluated.

The new yeast is associated with oropharyngeal candidiasis (oral thrush) in patients infected with the HIV virus, but has also been found in non-HIV-infected patients.

"The most useful test to distinguish the atypical isolates was a simple test of decreased growth of the Candida dubliniensis at increased temperatures (42 degrees C)," says Kirkpatrick. "Other biochemical and microscopic tests were not useful in distinguishing these strains, although identification was confirmed using a molecular probe of the yeast DNA. We have concluded that several mycological, biochemical and molecular techniques must be used to properly discriminate C. dubliniensis from C. albicans.

"Oral thrush is particularly prevalent in HIV-infected patients and also in patients with full blown AIDS," the researcher continues. "C. albicans is the most common causative agent. Other species, such as C. tropicalis and C. krusei, have become increasingly prominent pathogens, however."

Many of these unusual yeasts show resistance to commonly used antifungal therapies.

The new-found yeast, C. dubliniensis, was first identified in Ireland and was named after that country's capital city. It has previously been found in Australia, Europe and South America.

This work was supported by grants from the National Institute of Dental Research and the National Institutes of Health for the Frederic C. Bartter General Clinical Research Center, located at the South Texas Veterans Health Care System, and from Pfizer, Inc.

Contact: Jan Elkins (210) 567-2570