Yeast, molds, and cell types in 2 benchtop guides

Anne Ford

April 2013—During his six years overseeing fungal proficiency testing and assembling a library of fungal images on behalf of the CAP’s Microbiology Resource Committee, Gordon L. Love, MD, D(ABMM), noticed some-thing: Molds are surprisingly lovely.

“Fungi are the most beautiful of microorganisms, and molds are truly the flowers of the laboratory,” says Dr. Love, who is medical director of Quest Diagnostics’ Los Angeles laboratory in West Hills, Calif., medical director for the western region of Quest Diagnostics, and clinical professor of pathology at University of California, Davis, School of Medicine. He points to Chaetomium, a dematiaceous mold whose spined fruiting bodies float in the air and could be said to suggest dandelions.

And then there’s Aspergillus terreus. A mold with narrow, hyaline hyphae, it produces a cinnamon-tinted colony that looks sort of . . . delicious. “It almost looks like a cookie,” he says.

Not convinced? Thanks to the Mycology Benchtop Reference Guide: An Illustrated Guide for Commonly Encountered Fungi, a guide Dr. Love created on behalf of the CAP Microbiology Resource Committee as a user-friendly reference for laboratorians, you can judge for yourself (starting with the cover, which features Chaetomium in all its spined and fruiting glory).

Available since January, the guide describes essential characteristics—such as growth rates, colonial and microscopic morphology, and ecology—of 74 yeast and molds. The accompanying color photographs include colony and microscopic morphology for molds, as well as microscopic morphology for yeast. Also available since January is the Body Fluids Benchtop Reference Guide: An Illustrated Guide for Cell Morphology. Produced by six members of the CAP’s Hematology/Clinical Microscopy Resource Committee, it comprises photographs and discussions of 36 types of cells found in body fluid.

Like the CAP’s Hematology Benchtop Reference Guide, published in January 2012, the mycology and body fluids books are small, durable, spiral-bound volumes with water-resistant pages. They are designed to stand up to the wear and tear of benchtop use while providing users with a concise guide to the information most likely to be needed on a daily basis.

“We tried to make them resistant to fluids, et cetera, so they hold up at the bench, as opposed to reference books that don’t always do that,” says Joan E. Etzell, MD, who helped create the body fluids book. Dr. Etzell, chair of the Hematology/Clinical Microscopy Resource Committee, is a member of Contra Costa Pathology Associates and a medical director at John Muir Health’s MuirLab, Concord, Calif., and clinical professor of laboratory medicine at the University of California in San Francisco.

Every organism in the mycology guide, Dr. Love points out, has been not only morphologically identified but also sequenced and identified by molecular means. “I think that sets this book apart from other texts,” he says, “in that everything in here has been identified precisely.” Then, too, the guide alerts users to the terminology changes that many fungi have recently undergone. For example, the zygomycete formerly known as Absidia now bears the name Lichtheimia corymbifera complex. And while the Cladosporium genus once comprised pathogenic as well as nonpathogenic molds, the pathogenic molds have been moved primarily into the Cladophialophora genus.

In addition, “I tried to indicate those particular molds or yeast that have been recognized as potential problems to handle in the microbiology laboratory,” Dr. Love says. Among those is Cladophialophora bantiana, a dematiaceous—pigmented—mold and emerging fungal pathogen that’s been found to cause brain lesions in individuals with otherwise normal immune systems. If you find that alarming, you’re not the only one. “In the book, I caution that all molds should be processed only under laminar-flow, biological safety cabinets, but handling of this and certain other molds should be limited. In particular, slide cultures should not be made,” he stresses. “You just don’t want to disseminate it. If it’s inhaled, the medical technologist handling the culture could be at risk.”

He points, too, to Coccidioides immitis, a dimorphic fungus that’s “considered one of the very difficult molds to work with, the reason being that as the mold form grows, arthroconidia are produced in which hyphae break up into small segments,” he says. “These arthroconidia break off and can be inhaled into the lungs and cause disease. It’s been suggested that as few as 12 Coccidioides immitis arthrospores can cause disease in an immunocompetent individual. So this is a dangerous mold to work with.

“Now, in the microbiology laboratory,” he continues, “laminar-flow, biological safety cabinets are used, and the recommendation is that all molds are worked up in them. But these cabinets aren’t perfect; they can’t protect 100 percent of the time. When only a few arthroconidia can cause infection, Coccidioides immitis really has to be handled carefully. The handling of Coccidioides immitis should be limited to the minimum amount required to make the diagnosis.”

Coccidioides immitis is especially potentially dangerous because it’s easy to confuse with Malbranchea, a mold with narrow, hyaline hyphae that’s not associated with human disease. Dr. Love calls it “basically a contaminant.” But, like Coccidioides immitis, it produces alternating arthroconidia. While Coccidioides immitis arthroconidia are more swollen and produce thicker walls than those of Malbranchea, “in practice, that distinction may be difficult to establish with certainty,” he says. That’s why, as he writes in the guide, “Processing a potential Malbranchea culture carefully under a biological safety cabinet would be prudent.”