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Oral Fungi Offer Clue
to Candidiasis Therapy

This report is part of a 12-month Clinical Context series.

By Michael Smith, North American Correspondent, MedPage Today Published: October 23, 2011 Reviewed by Dori F. Zaleznik, MD; Associate Clinical Professor of Medicine, Harvard Medical School, Boston and Dorothy Caputo, MA, RN, BC-ADM, CDE, Nurse Planner

BOSTON - A study of the oral microbes in healthy and HIV-positive people has led to a new possibility for management of candidiasis, a researcher reported here.

Members of one yeast genus, Pichia, were never found in the same mouth as those of the genus Candida and vice versa, according to Mahmoud Ghannoum, PhD, of Case Western Reserve University in Cleveland.

The finding suggested that Pichia could inhibit Candida species, Ghannoum said during a featured oral presentation at the annual meeting of the Infectious Diseases Society of America.

And indeed, in lab tests, Pichia almost completely blocked the ability of Candida to form biofilms, which have an increased resistance to antifungal therapy, Ghannoum said.

The findings came from a project to characterize the so-called mycobiome of the mouth, or all of the fungal residents, in 20 healthy volunteers and again as a comparison between HIV-positive and HIV-negative volunteers.

In the 20 healthy volunteers, the researchers, using an advanced method of genetic sequencing, found 85 different genera and 101 species.

Among those found in more than 20% of samples, Candida species were the most frequent, being isolated from 75% of participants, Ghannoum reported. As well, Cladosporium species were found in 65% of the samples, followed by Aureobasidium, Saccharomycetales, Aspergillus, Fusarium, and Cryptococcus.

When the researchers compared the oral mycobiomes of the 12 HIV-negative volunteers with those of the 12 HIV-positive participants, they found some notable differences, he reported. Specifically:

  • The most common genus in both groups was Candida, but it was highly elevated in those with HIV.
  • Pichia, on the other hand, was not found among those with HIV and neither was Cladosporium.
  • Penicillium was seen at about the same level in both groups at 25%.
  • Ghannoum said the results indicated a shift in what he called the "core mycobiome" of the two groups, probably related to HIV infection. But intriguingly, the findings suggested that perhaps Pichia species inhibit Candida.

    To find out, the researchers compared the ability of Candida to form biofilms alone or in the presence of either Pichia or Penicillium .

    Biofilms formed in the presence of Pichia were significantly reduced ( P =0.019) compared to those formed by Candida alone, Ghannoum reported, and biofilms that were able to form were significantly thinner. In contrast, Penicillium had no significant effect (at P =0.509).

    The findings "support the notion that changes in the oral microbiota may have significant impact on human health and disease," Ghannoum said, adding that they "may lead to the development of novel approaches for the management of candidiasis in HIV-infected patients and other immune-compromised individuals."

    One important message of the study is that "the communities that live on us, and within us, are not just random collections of organisms," commented David Relman, MD, of Stanford University School of Medicine in Stanford, Calif., who was not part of the research but who moderated an IDSA press conference.

    The microbes have "a very important set of communication events and interactions that can be exploited, potentially, for maintaining or restoring health," he said.

    But he cautioned that the research is at an early stage and so far only shows associations, rather than causal links.

    The study was supported by the NIH and the Oral HIV/AIDS Research Alliance. Ghannoum said he had no disclosures.


    Primary source: Infectious Diseases Society of America
    Source reference:
    Ghannoum M, et al "Oral mycobiome and bacteriome analysis of HIV-infected patients and healthy individuals: Identification of Pichia as a Candida antagonist" IDSA 2011; Abstract 786.

    Source: MedPage Today
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