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 t he 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 respec t to the kinds and numbers of bacteria present and presence of soluble prot ein in cell-free supernatants. In addition, lipid extracts of pelleted cell s from fluids in BT-7415 were examined by gas chromatography/mass spectrosc opy for the kinds and relative amounts of phospholipid fatty acids (PLFA) p resent. A total of 19 different bacterial species was cultured and identifi ed, more than half (12/19) of which were gram-negative. Total colony-formin g units (CFU) reached levels of 2.2 x 10(3)/mL in BT-7415 and 2.4 x 10(5)/m L in BT-7707. The most common genus isolated was Pseudomonas. Estimations o f cell numbers based on total biomass from PLFA in samples from BT-7415 ind icated 1.1 x 10(7)/mL after 8 weeks of use. Both the numbers of PLFA identi fied and the amounts of each detected in BT-7415 increased as the fluids we re used. The chromatograms were dominated by two fatty acids, the amounts o f 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 ther e is an important component of the biological consortium in MWF that is not being detected by currently used culture techniques. There was no soluble protein detected in any of the samples from either system.