Factors influencing the microbial composition of metalworking fluids and potential implications for machine operator’s lung

Hypersensitivity pneumonitis, also known as “machine operator’s lung” (MOL), has been related to microorganisms growing in metalworking fluids (MWFs), especially Mycobacterium immunogenum. During the present study, the authors described the microbiological contamination of MWFs and looked for chemical, physical, and environmental parameters associated with variations in microbiological profiles. The authors microbiologically analysed 180 MWF samples from nonautomotive plants (e.g.,screw-machining or metal-cutting plants) in the Franche-Comte region in eastern France and 165 samples from three French automotive plants in which cases of MOL had been proven. The results revealed two types of microbial biomes: the first was from the nonautomotive industry, showed predominantly Gram-negative rods (GNR), and was associated with a low risk of MOL, and the second came from the automotive industry that was affected by cases of MOL and showed predominantly Gram-positive rods (GPR). Traces of M. immunogenum were sporadically detected in the first type, while it was highly prevalent in the automotive sector, with up to 38% of samples testing positive. The use of chromium, nickel, or iron was associated with growth of Gram-negative rods; conversely, growth of Gram-positive rods was associated with the absence of these metals. Synthetic MWFs were more frequently sterile than emulsions. Vegetable oil-based emulsions were associated with GNR, while mineral ones were associated with GPR. The authors concluded that the findings from this study suggest that metal types and the nature of MWF play a part in MWF contamination. This work shall be followed by further in vitro simulation experiments on the kinetics of microbial populations, focusing on the phenomena of inhibition and synergy.