Research Article: First Cultivation and Characterization of Mycobacterium ulcerans from the Environment

Date Published: March 26, 2008

Publisher: Public Library of Science

Author(s): Françoise Portaels, Wayne M. Meyers, Anthony Ablordey, António G. Castro, Karim Chemlal, Pim de Rijk, Pierre Elsen, Krista Fissette, Alexandra G. Fraga, Richard Lee, Engy Mahrous, Pamela L. C. Small, Pieter Stragier, Egídio Torrado, Anita Van Aerde, Manuel T. Silva, Jorge Pedrosa, Mathieu Picardeau

Abstract: BackgroundMycobacterium ulcerans disease, or Buruli ulcer (BU), is an indolent, necrotizing infection of skin, subcutaneous tissue and, occasionally, bones. It is the third most common human mycobacteriosis worldwide, after tuberculosis and leprosy. There is evidence that M. ulcerans is an environmental pathogen transmitted to humans from aquatic niches; however, well-characterized pure cultures of M. ulcerans from the environment have never been reported. Here we present details of the isolation and characterization of an M. ulcerans strain (00-1441) obtained from an aquatic Hemiptera (common name Water Strider, Gerris sp.) from Benin.Methodology/Principal FindingsOne culture from a homogenate of a Gerris sp. in BACTEC became positive for IS2404, an insertion sequence with more than 200 copies in M. ulcerans. A pure culture of M. ulcerans 00-1441 was obtained on Löwenstein-Jensen medium after inoculation of BACTEC culture in mouse footpads followed by two other mouse footpad passages. The phenotypic characteristics of 00-1441 were identical to those of African M. ulcerans, including production of mycolactone A/B. The nucleotide sequence of the 5′ end of 16S rRNA gene of 00-1441 was 100% identical to M. ulcerans and M. marinum, and the sequence of the 3′ end was identical to that of the African type except for a single nucleotide substitution at position 1317. This mutation in M. ulcerans was recently discovered in BU patients living in the same geographic area. Various genotyping methods confirmed that strain 00-1441 has a profile identical to that of the predominant African type. Strain 00-1441 produced severe progressive infection and disease in mouse footpads with involvement of bone.ConclusionStrain 00-1441 represents the first genetically and phenotypically identified strain of M. ulcerans isolated in pure culture from the environment. This isolation supports the concept that the agent of BU is a human pathogen with an environmental niche.

Partial Text: Buruli ulcer (BU), the third most common mycobacteriosis in humans after tuberculosis and leprosy is an indolent, necrotizing disease of skin, subcutaneous tissue and, occasionally, bones [1]. BU has emerged in recent times as an increasingly important cause of morbidity around the world, and has been reported in 30 countries, mostly in tropical areas [2]. This disease is caused by Mycobacterium ulcerans which is peculiar among pathogenic mycobacteria because it produces a potent necrotizing exotoxin, mycolactone, which is a major virulence factor [3].

The prevailing concept that BU is associated with wetlands, especially slow-flowing or stagnant water, implies that M. ulcerans is an environmental pathogen transmitted to humans from particular aquatic niches. Historically, the presence of M. ulcerans in aquatic samples, including water, mud, aquatic plants, aquatic insects, aquatic mollusks, crustacea and small fish, has been inferred from the detection by PCR of the insertion sequence IS2404, highly represented in the genome of M. ulcerans[14]. All previous attempts to isolate fully characterized M. ulcerans from environmental samples, however, have failed, and recent evidence [22] indicates that IS2404 positivity alone is inadequate to establish the presence of M. ulcerans in environmental samples.



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