Relative Formaldehyde Resistance Among Bacterial Survivors of Biocide-Treated Metalworking Fluid

Surviving Gram-negative bacterial populations of a metalworking fluid, soluble-oil emulsion, exposed to aformaldehyde (FAJ-based industrial biocide were isolated and identified. Resistance of isolates to FA and FA-based biocides was determined and significant differences were noted. The most resistant strain survived 25 mM FA when tested in tryptic soy broth. Attempts to induce greater resistance in less resistant isolates yielded mixed results. The FA -resistant isolates were shown to be cross-resistant to a number of FA -based biocides. Detoxification (removal) of FA by mixtures of FA-resistant and FA-sensitive organisms was a function of the level of resistant organism present. This may explain the varied resistance levels among isolates from a single system to FA. The results suggest that protection of susceptible strains by resistant organisms may occur under field conditions.