Mycobacteria of Runyon groups I, II and IV do not play an aetiological role in Crohn??s disease

Abstract

In addition to Mycobacterium paratuberculosis, other slow-growing as well as rapid-growing mycobacteria were isolated from mucosa or full thickness samples of intestine from patients with Crohn's disease. The meaning of these data remained unclear. To investigate the possible aetiological role of these rapid- and slow-growing mycobacteria, serosa and mesenteric lymph nodes were also cultivated in the present study. Mucosa, lymph nodes and serosa of 23 patients with Crohn's disease and 23 patients with other intestinal afflictions were incubated at 37 degrees C on Löwenstein-Jensen medium and Herrold egg yolk medium. These methods allow the cultivation of most atypical mycobacteria, including Mycobacterium paratuberculosis. In addition, full thickness samples of some of these patients were analysed for mycobacterial DNA using polymerase chain reaction. Despite lack of decontamination of 60% of lymph nodes and serosa, no mycobacterial growth was observed over a long incubation period (an average of 718 days in Crohn's disease and 552 days in controls) on Löwenstein-Jensen medium. Polymerase chain reaction was based on the amplification of 16S ribosomal DNA sequences specific for mycobacteria of tissues derived from four patients with Crohn's disease and one control was negative. These findings suggest that mycobacteria, such as M. fortuitum and M. chelonei, which are widespread in the environment, are not involved in the aetiology of Crohn's disease but, rather, should be considered as environmental opportunists.