Abstract
Mycobacterium canettii is a smooth bacillus related to the Mycobacterium tuberculosis complex. It causes lymph nodes and pulmonary tuberculosis in patients living in countries of the Horn of Africa, including Djibouti. The environmental reservoirs of M. canettii are still unknown. We aimed to further decrypt these potential reservoirs by using an original approach of High-Throughput Carbon and Azote Substrate Profiling. The Biolog Phenotype profiling was performed on six clinical strains of M. canettii and one M. tuberculosis strain was used as a positive control. The experiments were duplicated and authenticated by negative controls. While M. tuberculosis metabolized 22/190 (11%) carbon substrates and 3/95 (3%) nitrogen substrates, 17/190 (8.9%) carbon substrates and three nitrogen substrates were metabolized by the six M. canettii strains forming the so-called corebiologome. A total at 16 carbon substrates and three nitrogen substrates were metabolized in common by M. tuberculosis and the six M. canettii strains. Moreover, at least one M. canettii strain metabolized 36/190 (19%) carbon substrates and 3/95 (3%) nitrogen substrates for a total of 39/285 (13%) substrates. Classifying these carbon and nitrogen substrates into ten potential environmental sources (plants, fruits and vegetables, bacteria, algae, fungi, nematodes, mollusks, mammals, insects and inanimate environment) significantly associated carbon and nitrogen substrates metabolized by at least one M. canettii strain with plants (p = 0.006). These results suggest that some plants endemic in the Horn of Africa may serve as ecological niches for M. canettii. Further ethnobotanical studies will indicate plant usages by local populations, then guiding field microbiological investigations in order to prove the definite environmental reservoirs of this opportunistic tuberculous pathogen.
Highlights
Mycobacterium canettii is a smooth tubercle bacillus isolated by G
M. canettii CIP 140010059T, M. canettii DJ480, M. canettii DJ734, M. canettii DJ514, M. canettii DJ517 and M. canettii DJ613 were isolated from clinical sources in Djibouti in 2016 [4] and M. tuberculosis Beijing family was used as a positive control [10]
For M. canettii, 17 carbon substrates and three nitrogen substrates were metabolized by the six M. canettii strains under investigation, forming the so-called corebiologome (Table 3)
Summary
Mycobacterium canettii is a smooth tubercle bacillus isolated by G. Canetti in 1969 and belonging to the Mycobacterium tuberculosis complex [1]. Environmental reservoirs of M. canettii reported in the literature, and most of these patients have been infected in the Horn of Africa and in Djibouti [2, 3]. We confirmed that M. canettii was still circulating in the Horn of Africa by isolating M. canettii strains from patients presenting with pulmonary tuberculosis in Djibouti [4]. Initial molecular analysis of a large collection of M. canettii isolates revealed a high genetic diversity with traces of intraspecies horizontal gene transfer [5]. Whole genome sequencing analysis of five representative isolates showed that M. canettii was the M. tuberculosis complex species most closely related to the last common progenitor of this complex [6]
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