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New Color Atlas aids in identifying fungal species

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October 2018—CAP Press released in October the Color Atlas of Mycology, by Gordon Love, MD, D(ABMM), and Julie Ribes, MD, PhD. Its 388 pages hold more than 800 tables and images, with identifications verified by DNA sequencing (for images post-2009). Here, in an exchange with CAP TODAY, Dr. Love explains how this atlas stands apart from others in the Color Atlas series and from others on the market.

Dr. Love is chair of the Department of Pathology, Louisiana State University School of Medicine, and director of laboratories, University Medical Center, New Orleans.

Can you explain the concept of a field guide based on proficiency testing and why this field guide is useful in evaluating PT?
The Color Atlas of Mycology is based on proficiency testing results over a 16-year period in which fungal identification was guided by participant performance. The user-friendly presentations of images and text in the atlas show how to correctly identify as well as how to avoid misidentifying fungal challenges, whether proficiency testing or patient isolates. As an example, the use of Fonsecaea pedrosoi in FA-2002 resulted in an erroneous identification of Sporothrix schenckii by 47 participants. Both are dematiaceous (pigmented) molds that may form conidia along hyphae and conidiophores, but in the case of F. pedrosoi, elongated conidia may form asterisk formations (see image). Comparison of photographs make distinctions easier. This approach produced a mycology field guide that is uniquely suited to discuss the variations in fungal morphology that mycologists encounter in practice.

The process of identifying PT specimens should be identical to that of identifying routine clinical specimens. This atlas provides insights into the CAP mycology PT process. An advantage involves knowledge of previous challenges. The CAP Microbiology Resource Committee maintains a stored set of fungi for PT use. This stored set contains a restricted number of fungi that have been vetted by sequencing, with additions occurring relatively infrequently. A PT participant can easily review the 16-year history of mycology PT in this atlas but should realize that a new fungus could have been added recently. When entertaining any particular fungal diagnosis, distractors, as identified by previous PT, should be eliminated, and this thought process should be equally applicable to PT and isolates from clinical specimens.

From Fig. 96-3. Pattern of conidiation of Fonsecaea pedrosoi. Arrows indicate asterisk conidiation.

From Fig. 96-3. Pattern of conidiation of Fonsecaea pedrosoi. Arrows indicate asterisk conidiation.

Your atlas is different in a few ways from previous atlases in the Color Atlas series. How so?
Most of the fungi, post-2008–2009, described in this Color Atlas of Mycology have been verified by DNA sequencing. This is in contrast to reliance on expert opinion and consensus as applied to morphology. Another way that the Color Atlas of Mycology differs from other Color Atlas titles is in the comprehensive use of PT data. All participant classifications for 16 years are reviewed. These identification decisions of PT participants defined the differential diagnoses. In the atlas, the adjacent comparisons of photographs of the correct and incorrect mold or yeast aid understanding. Other atlases in the Color Atlas series used photographs that had been distributed originally as PT challenges. The Color Atlas of Mycology is based on PT of organisms that live and then die and thus are unavailable for further study. Mycology PT examples after 2006 were documented by photographing the original challenges. For 2000–2006, the CAP did not keep microscopic photographs of challenges, but in some cases we were able to find photographs or glass slides in our personal collections.

Some important molds such as Coccidioides species have never been distributed for PT due to dangers in handling. We filled the gaps with yeast and molds collected in our mycology practices in order to make the Color Atlas of Mycology comprehensive. Some photographs were obtained from the pictorial library of the Centers for Disease Control and Prevention, and others were used by permission.

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