Biofilms in Granuloma Annulare

Herbert B Allen*, Rina M Allawh , Mary Larijani , Carrie A Cusack

Department of Dermatology, Drexel University College of Medicine, Philadelphia, Pennsylvania, United States

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Alle HB, Allawh RM, Larijani M, Cusack CA. Biofilms in granuloma annulare. Clin Dermatol Dermatitis. 2019 Mar;2(1):111


In this preliminary study, we evaluate 10 skin specimens with a previous clinical and pathological diagnosis of granuloma annulare (GA) for biofilms with staining methods we have employed in skin and other diseases. Biofilms consist of two key ingredients: polysaccharides and amyloid. The stains used for polysaccharides were periodic acid Schiff (PAS) and colloidal iron and, for amyloid, Congo red. All ten specimens showed staining for both components revealing the presence of biofilms in GA. Because microbes create biofilms, GA, by definition, is a microbial disease, and it joins many other cutaneous diseases, such as psoriasis and eczema, with biofilms created by microbes. The identification of the specific microbe in GA awaits further investigation.


Biofilms; Granuloma annulare; Skin diseases


We have considered staining pathologically for biofilms in granuloma annulare (GA) because one half of the required process has been long been completed and accepted. That one half is staining for mucin which has been noted to be positive for more than 50 years [1]. The mucin in biofilms is composed of extracellular polysaccharides that surround the microbes [2]. The other one half is staining for amyloid with Congo red (CR); the amyloid acts as infrastructure for the biofilms [2]. With this approach, substantiated by microbiological assays, we have shown that biofilms are present in the skin in many other cutaneous diseases including atopic dermatitis, seborrheic dermatitis, tinea pedis, Doucas Kapetanakis, Meyerson’s nevus, axillary granular parakeratosis, molluscum contagiosum (MC), all forms of eczema nummular, dyshidrotic, etc.), tinea versicolor, and healing wounds [3-6]. We have also identified skin diseases in which the pathological biofilms are found in other organs and not the skin. Specifically, these are psoriasis which has biofilms in the tonsils; leprosy, where the biofilms are in the liver, spleen, and kidney (and only in the skin as “globi” in late lepromatous leprosy); tertiary Lyme disease, where biofilms have been noted in the joints and brain (Lyme arthritis and Alzheimer’s disease) [7-9].

The biofilms are created by different microbes: normal flora staphylococci in eczema, streptococci in psoriasis, molluscum virus in molluscum contagiosum, yeasts in tinea versicolor, mycobacteria in leprosy, and spirochetes in Lyme disease [3-5,7-9].

Inasmuch as we have been pursuing a “proof of concept” in this preliminary effort, we used biopsies that had been taken from the ringed, non-scaling plaques of GA that form the majority of the presentations of that disease. Not included were deep GA, disseminated GA or interstitial granulomatous dermatitis [1].


Ten specimens from 6F and 4M aged 6-22 were initially examined and diagnosed as GA both clinically and with routine pathology. Periodic acid Schiff (PAS), colloidal iron (which stains for acidic mucin), and CR stains were also performed on theses specimens. The findings were confirmed by 4 dermatopathologists. As controls, 10 specimens from healing wounds were examined with the same staining.


On reexamination, all ten specimens showed the expected pathological findings of dermal necrobiotic granulomas surrounded by a lymphohistiocytic infiltrate. With PAS and colloidal iron, positive staining for mucin was shown in the necrobiotic zones of the lesions (Figures 1 & 2). Also, all ten showed positive staining with CR (Figure 3). Ten specimens from healing wounds showed changes only in the eccrine ductal occlusions as previously identified and not in the dermis as seen in GA (Figure 4).

Figure 1: Granuloma annulare pathology-H+E stained section of skin showing necrobiotic granulomas in the dermis. Mucin in the granulomas shows gray-blue staining (5X)