Mycobacterial contamination of metalworking fluids: Involvement of a possible new taxon of rapidly growing mycobacteria

Contamination of air and metalworking fluid (MWF) systems with a rapidly gr owing mycobacterium (RGM) was detected in 1995 in a single manufacturing pl ant with recent cases of hypersensitivity pneumonitis (HP). Extensive envir onmental sampling was performed to determine the extent of the contaminatio n and its variability over time. RGM were present in multiple indoor air sa mples, 100% of the central MWF storage tanks, and 75% of the freestanding c utting, drilling, and grinding machines. With one exception, contamination was limited to a recently introduced formulation (brand) of semisynthetic M WF used in 95% of the facility's machining operations. In general, the myco bacterial counts were stable over time, with the degree of contamination ra nging from 10(2)-10(7) colony forming units (CFU)/mL. A few systems were cu lture positive for the mycobacterium (>10(1) CFU/mL), changed to culture ne gative (<10(1) CFU/mL), then changed back to culture positive without expla nation. Samples obtained from diluted (5%) but unused MWF, a replenishment line with 2% unused MWF, an MWF pasteurizer, city water, and deionized wate r were culture negative for this species of mycobacterium. Inoculation and growth studies demonstrated that this mycobacterium does not grow in liquid samples of 5% unused MWF. By molecular techniques, the mycobacterial isola tes consisted of a single strain and represented a previously undescribed t axon closely related to Mycobacterium chelonae/abscessus. The relationship of this mycobacterium to the cases of HP is unknown.