Microbial contamination and biofilms on machines of metal industry using metalworking fluids with or without biocides

Microbial contamination is commonly found in metalworking fluids (MWFs) used in metal manufacturing industry. The aim of this study was to determine whether the use of MWF containing a biocide reduces the growth and influences the biofilm-forming capacity of microorganisms from field coolants, thereby efficiently protecting MWFs from biodeterioration. Overall, 164 bacterial strains classified into 40 species were collected from 69 machines in ten plants visited. Among them, Comamonas testosteroni was the most numerous species, and Pseudomonas was the most abundant genus. The isolation of Mycobacterium immunogenum was done from MWF for the first time in Poland. The number of bacteria in MWFs and size of microbial populations in biofilms were not affected by the presence of biocides in the industrial samples. In MWFs contaminated with microorganisms with the highest biofilm-forming capacity, several species of Enterobacteriaceae were identified. The proper management of MWF delivery systems is required to control biofilm development even when MWFs containing biocides are used. Moreover, good hygiene practices are needed to prevent the metal working machines from biofilms. This case study can help in appropriate monitoring the MWF distribution systems vulnerable to microbial colonization in metal industry.