Expanding the mycobacterial diversity of metalworking fluids (MWFs): evidence showing MWF colonization by Mycobacterium abscessus

Abstract

Nontuberculous mycobacteria (NTM) have been associated with hypersensitivity pneumonitis in machinists. Only two species of NTM, namely Mycobacterium immunogenum and Mycobacterium chelonae, have been reported thus far to have the ability to colonize contaminated metalworking fluids (MWFs). Here, we report, for the first time, the presence and characterization (phenotypic and genotypic) of a third species, Mycobacterium abscessus, colonizing these harsh alkaline machining fluids. Two Mycobacterium morphotypes, smooth (S) and rough (R), were isolated (two isolates each) from an in-use industrial MWFs. Biocide susceptibility analysis using triclosan as a model yielded the same minimal inhibitory concentration for the two morphotypes. PCR-restriction analysis-based speciation of the morphotypes confirmed their identity as M. abscessus. Genotyping based on partial DNA sequences corresponding to the variable regions of the hsp65 gene and 16S-23S rRNA operon internal transcribed spacer region and randomly amplified polymorphic DNA-PCR analysis showed that both morphotypes belong to a single genotype. In addition, we isolated and confirmed two novel mycobacterial genotypes, one each of M. immunogenum and M. chelonae from additional in-use MWF screening. Taken together, this study expands the known mycobacterial species- and strain-diversity colonizing MWF. Furthermore, the study emphasizes the need for including M. abscessus species in the existing mycobacterial screening of contaminated MWF.