Presence of Acinetobacter species among the predominant bacteria found in a contaminated metal-working fluid

Abstract

The distribution of Acinetobacter species among the bacteria isolated from an unusually heavily contaminated petroleum-based water-soluble metal-working fluid used in a large North American automotive machining operation was investigated. It had been found previously1 that, in laboratory cultures with metal-working fluids as the sole carbon source, these species grew more rapidly and to much higher densities than any other types of bacteria isolated from this system. Thus, it was expected that they would dominate the population and would be difficult to control. It is shown here that, contrary to expectation, over a one-year period Acinetobacter species usually accounted for only a few percent of the total population. Factory fluids did not contain substances that selectively inhibited the growth of these species. In mixed-cultures grown in the laboratory with metal-working fluid as the carbon source, Acinetobacter species accounted for less than 1% in the initial inocolum, nearly 70% during the mid-exponential-phase, and only a few percent in the stationary-phase. These experiments suggest, as a working hypothesis, that the Acinetobacter species `govern' the contamination in the sense that they first colonize the fluid and their presence is necessary to maintain the other strains.