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Abstract
Mycobacterium chelonae is an important, rapidly growing, acid-fast bacterium that causes opportunistic disease in humans and fatal disease in aquatic animals. Organisms in the M. chelonae-abscessus complex (MCAC), including M. chelonae and M. abscessus subsp. abscessus, are difficult to differentiate. Many proposed methods to identify isolates in the MCAC exist but have been proven inadequate in diagnostic settings. Furthermore, standard break-points for species identification have yet to be established. As a result, these bacteria are often misidentified. Of the numerous aquatic species held in captivity, fish in the Family Syngnathidae, the seadragons, seahorses, and pipefish, are highly susceptible to disease caused by M. chelonae. Syngnathids infected with M. chelonae present with disseminated disease that appears more acute, typically without granuloma formation, when compared to other vertebrates. The objectives of this study were to: (1) evaluate clinical isolates previously identified as M. chelonae cultured from biofilms, syngnathids, teleosts, reptiles, and mammals, including humans by comparing 11 targeted genetic loci, hsp65 PRA, and minimum inhibitory concentrations to antimicrobial drugs, (2) consider whole genome sequencing with core extraction to evaluate true phylogenetic placement of M. chelonae isolates and their relationship to each other, as well as type strains of nontuberculous mycobacteria, (3) characterize the histologic lesions of mycobacteriosis in syngnathids, and (4) describe the transcriptome of the lined seahorse, Hippocampus erectus, naturally infected with M. chelonae. Results identified whole genome sequencing as an ideal method for phylogenomic placement of closely related M. chelonae isolates, several of which had been previously misidentified. Findings indicate the current M. chelonae reference strain, ATCC 35752, is not representative of current clinical isolates, while M. chelonae ATCC 19237 is representative and represents a subspecies of M. chelonae. Breakpoints for species designation using targeted gene sequencing were proposed. A non-tuberculous species was identified in two syngnathids. There was no host specificity with relation to strain, but host lesions did vary by species affected. Syngnathids have a different presentation of mycobacteriosis than other teleosts. While components of the innate immune system were identified, components in the adaptive system important to controlling mycobacteriosis were not and may underlie their unique pathological presentation.