Date Published: October 31, 2007
Publisher: Public Library of Science
Author(s): Daniela Schütte, Alphonse Um-Boock, Ernestina Mensah-Quainoo, Peter Itin, Peter Schmid, Gerd Pluschke, Pamela L. C. Small
Abstract: BackgroundBuruli ulcer caused by Mycobacterium ulcerans is an infection of the subcutaneous tissue leading to chronic necrotising skin ulcers. The pathogenesis is associated with the cytocidal and immunosuppressive activities of a macrolide toxin. Histopathological hallmark of progressing disease is a poor inflammatory response despite of clusters of extracellular bacilli. While traditionally wide excision of the infected tissue was the standard treatment, provisional WHO guidelines now recommend an eight week pre-treatment with streptomycin and rifampicin.Methodology/Principal FindingsWe conducted a detailed immunohistochemical analysis of tissue samples from Buruli patients who received antibiotic treatment. Cellular immune response along with bacterial load and distribution were monitored. We demonstrate that this treatment leads to the development of highly organized cellular infiltration surrounding areas of coagulative necrosis. Diffuse infiltrates, granulomas and dense lymphocyte aggregation close to vessels were observed. Mycobacterial material was primarily located inside mononuclear phagocytes and microcolonies consisting of extracellular rod-shaped mycobacteria were no longer found. In observational studies some patients showed no clinical response to antibiotic treatment. Corresponding to that, one of five lesions analysed presented with huge clusters of rod-shaped bacilli but no signs of infiltration.Conclusions/SignificanceResults signify that eight weeks of antibiotic treatment reverses local immunosuppression and leads to an active inflammatory process in different compartments of the skin. Structured leukocyte infiltrates with unique signatures indicative for healing processes developed at the margins of the lesions. It remains to be analysed whether antibiotic resistance of certain strains of M. ulcerans, lacking patient compliance or poor drug quality are responsible for the absent clinical responses in some patients. In future, analysis of local immune responses could serve as a suitable surrogate marker for the efficacy of alternative treatment strategies.
Partial Text: Buruli ulcer (BU) caused by Mycobacterium ulcerans is a chronic necrotizing skin disease mainly affecting subcutaneous and adipose tissue [1,2]. The unique pathology of BU is primarily attributed to a plasmid-encoded macrolide toxin, mycolactone [3,4]. Mycolactone has cytopathic and apoptotic activity and is thought to be responsible for local immunosuppression by destroying infiltrating cells [3,5,6]. In animal models, injection of purified mycolactone causes lesions similar to those produced by wild type M. ulcerans bacteria [3,7].
It has been demonstrated recently that treatment with a combination of rifampicin and streptomycin inhibits the growth of M. ulcerans in pre-ulcerative BU lesions . Furthermore, observational studies  indicate that at least in some of the BU patients antibiotic therapy may reduce the extent of or even circumvent the indication for surgery. Here we present results of a detailed immunohistological analysis of ulcerative BU lesions from patients treated with rifampicin/streptomycin prior to surgery. Findings were compared to those obtained from lesions of patients that have been treated merely with wide-ranging surgical excision (Figure 1) according to former WHO treatment guidelines [1,18]. To our knowledge this is the first detailed immunohistological description of the effect of antibiotic treatment on BU lesions.