Mycobactin analysis as an aid for the identification of Mycobacterium fortuitum and Mycobacterium chelonae subspecies

Abstract

Mycobactin patterns from 65 Mycobacterium fortuitum and Mycobacterium chelonae strains have been determined by thin-layer chromatography. By use of a rich liquid medium containing an iron chelator (ethylenediamine-di-o-hydroxyphenylacetic acid [EDDA]) to ensure iron starvation, all strains were able to form mycobactins. The method developed here allows sensitive detection of mycobactin by thin-layer chromatography from as little as 5 ml of culture after a 2-week incubation. Within M. fortuitum two mycobactin patterns were identified, whereas within M. chelonae four were recognized. Comparisons with the subspecific identification performed by using biochemical tests showed that 73% of the M. fortuitum subsp. fortuitum strains shared the same mycobactin pattern (designated F), whereas 75% of the M. fortuitum subsp. peregrinum strains shared the other mycobactin pattern (designated P). Within the M. fortuitum strains that cannot be assigned to a subspecies on the basis of their biochemical features, only F and P patterns were determined. Similarly, 93% of the M. chelonae subsp. chelonae strains produced the so-called C1 and C2 patterns and 86% of the M. chelonae subsp. abscessus strains produced A1 and A2 patterns. C2 and A2 were the patterns most frequently encountered; they were represented by 65 and 50% of the M. chelonae subsp. chelonae and M. chelonae subsp. abscessus strains, respectively. Within the biochemically M. chelonae strains that did not fit any subspecies on the basis of biochemical test results, C1, C2, and A1 patterns were found. Whereas about 30% of both M. fortuitum and M. chelonae strains cannot be characterized to the subspecies level on the basis of biochemical tests, 100% of the strains of both species can be characterized on the basis of mycobactin patterns.