A pilot study for monitoring changes in the microbiological component of metalworking fluids as a function of time and use in the system.

This article describes the results of a pilot study to examine changes in the biological component of metalworking fluids (MWF) as a function of use. Fluid samples were taken from two newly charged systems, designated BT-7415 and BT-7707, at 1-week intervals for 8 weeks and characterized with respect to the kinds and numbers of bacteria present and presence of soluble protein in cell-free supernatants. In addition, lipid extracts of pelleted cells from fluids in BT-7415 were examined by gas chromatography/mass spectroscopy for the kinds and relative amounts of phospholipid fatty acids (PLFA) present. A total of 19 different bacterial species was cultured and identified, more than half (12/19) of which were gram-negative. Total colony-forming units (CFU) reached levels of 2.2 x 10(3)/mL in BT-7415 and 2.4 x 10(5)/mL in BT-7707. The most common genus isolated was Pseudomonas. Estimations of cell numbers based on total biomass from PLFA in samples from BT-7415 indicated 1.1 x 10(7)/mL after 8 weeks of use. Both the numbers of PLFA identified and the amounts of each detected in BT-7415 increased as the fluids were used. The chromatograms were dominated by two fatty acids, the amounts of which increased with time. These fatty acids, 18:2 omega 6 and 18:1 omega 9c, are not commonly associated with pseudomonads. This suggests that there is an important component of the biological consortium in MWF is not being detected by currently used culture techniques. There was no soluble protein detected in any of the samples from either system.