Extended tracking of the microbial community structure and dynamics in an industrial synthetic metalworking fluid system.

Understanding of the occupational exposure risk scenario and disease etiology associated with industrial metalworking fluids (MWFs) requires knowledge of the development and composition of their microbial diversity in relation to the underlying fluid management factors. In this study, a managed synthetic MWF operation freshly recharged following the dumping, cleaning, and recharge (DCR) process was tracked in real time for microbial community changes over a period of 1.25 years (65 weeks). The recharged fluid developed very high bacterial counts (viable and nonviable) fairly quickly after the DCR process, indicating its inadequacy. Genus-/group-specific real-time qPCR confirmed the prevalence of six potentially pathogenic/immunogenic microbial genera/groups, viz. pseudomonads, enterics, mycobacteria, legionellae, actinomycetes, and fungi. Selective culturing revealed Acinetobacter and Bacillus as the most frequently isolated Gram-negative and Gram-positive genera, respectively, in addition to the presence of fungi and actinomycetes. Endotoxin perturbations (< 1000 to > 100000 EU mL⁻¹) coincided with temporal increases in Gram-negative bacteria and/or periodic biocide additions. PCR-DGGE-sequencing revealed an expanded estimated bacterial richness (up to 23 bands per sample). Of the 16 dominant bacterial phylotypes identified, the majority were detected for the first time in MWF. Interestingly, the study revealed a crucial role for MWF brand, among other fluid factors, in modulating the community structure and dynamics.