J Pathol Transl Med.  2017 Sep;51(5):482-487. 10.4132/jptm.2017.07.11.

Acid-Fastness of Histoplasma in Surgical Pathology Practice

• Rajeshwari M
• Xess I
• Sharma MC
• Jain D

• KMID: 2392567
• DOI: http://doi.org/10.4132/jptm.2017.07.11

Abstract

BACKGROUND
Histoplasmosis (HP) is diagnosed by visualizing intracellular microorganisms in biopsy and/or culture. Periodic-acid Schiff (PAS) and Gomori methenamine silver (GMS) staining methods are routinely used for identification. The acid-fast property of Histoplasma was identified decades ago, but acid-fast staining has not been practiced in current surgical pathology. Awareness of the acid-fast property of Histoplasma, which is due to mycolic acid in the cell wall, is important in distinguishing Histoplasma from other infective microorganisms. Here, we examined acid-fastness in previously diagnosed cases of Histoplasma using the Ziehl-Neelsen (ZN) stain and correlated those findings with other known fungal stains.
METHODS
All cases diagnosed as HP were retrieved and reviewed along with ZN staining and other fungal stains. We also stained cases diagnosed with Cryptococcus and Leishmania as controls for comparison.
RESULTS
A total of 54 patients ranging in age from 11 to 69 years were examined. The most common sites of infection were the skin, adrenal tissue, and respiratory tract. Of the total 43 tissue samples, 20 (46.5%) stained positive with the ZN stain. In viable cases, a significant proportion of microorganisms were positive while necrotic cases showed only rare ZN-positive yeasts. In comparison to PAS and GMS stains, there was a low burden of ZN-positive yeasts. Cryptococcus showed characteristic ZN staining and all cases of Leishmania were negative.
CONCLUSIONS
Although the morphology of fungal organisms is the foundation of identification, surgical pathologists should be aware of the acid-fast property of fungi, particularly when there is the potential for confusion with other infective organisms.

Keyword

Histoplasma; Acid fast; Ziehl-Neelsen; Fungal organisms

MeSH Terms

Biopsy
Cell Wall
Coloring Agents
Cryptococcus
Fungi
Histoplasma*
Histoplasmosis
Humans
Leishmania
Methenamine
Mycolic Acids
Pathology, Surgical*
Respiratory System
Skin
Yeasts
Coloring Agents
Methenamine
Mycolic Acids

Figure

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  Fig. 1. (A) Photomicrograph of a histoplasmosis case showing Ziehl-Neelsen (ZN)-negative yeasts. (B) Skin biopsy showing ZN-positive Histoplasma yeast cells (arrows); ZN-positive hair shaft in a hair follicle is shown for color comparison. (C, D) Two different cases show numerous to few ZN-positive yeast cells.

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  Fig. 2. (A) Photomicrograph shows numerous extracellular and intracellular Histoplasma yeast cells present within a giant cell. Histoplasma are round to oval in shape with an eccentric purple dot or crescent. (B, C) Periodic-acid Schiff and Gomori methenamine silver stains highlight fungal profiles.

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  Fig. 3. Oil immersion magnification of periodic-acid Schiff (A) and Gomori methenamine silver (B) Histoplasma stains.

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  Fig. 4. (A) A case of cryptococcal infection involving bone marrow shows numerous fungal organisms that are round in shape and surrounded by a clear space. (B) Ziehl-Neelsen staining highlights all cryptococci and surrounding capsular halos with magenta color.

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