eJournals International Colloquium Tribology 23/1

International Colloquium Tribology
ict
expert verlag Tübingen
125
2022
231

Do Biofilms in Metalworking Fluid Systems Matter?

125
2022
Frederick J. Passman
ict2310091
23rd International Colloquium Tribology - January 2022 91 Do Biofilms in Metalworking Fluid Systems Matter? Frederick J. Passman Biodeterioration Control Associates, Inc., Princeton, New Jersey, United States Corresponding author: fredp@biodeterioration-control.com 1. Introduction Historically, condition monitoring for microbial contamination has focused on measuring bioburdens in bulk fluid samples. However, biofilm communities create several significant metalworking fluid (MWF) management challenges. First, they are non-uniform. Samples must be collected from diagnostic, rather than representative locations. Second, biofilms are resistant to microbicide treatments. Third, biofilms readily reinfect recirculating MWF once the microbicide concentration has decreased to less than its critical concentration. Although the use of bioresistant MWF has decreased the need for microbicide tankside additions to control planktonic populations, it has not necessarily reduced the risk of bioaerosol generation. This paper will address the importance of biofilm bioburden monitoring and control, and the implications of effective control on bioaerosol exposures. 2. Biofilm Composition In ASTM Practice E2169 [1] a biofilm is defined as a film or layer composed of microorganisms, biopolymers, water, and entrained organic and inorganic debris that forms as a result of microbial growth, proliferation, and excretion of polymeric substances at phase interfaces (liquid-liquid, liquid-solid, liquid-gas, and so forth). Diverse species of bacteria and fungi can be detected in biofilm communities or consortia. Importantly, depending on its location within a biofilm matrix, a given type of microbe (genetic type - operational taxonomic unit, OTU) can have substantially different morphologies (just as human cell morphologies vary) and physiological properties. Moreover, microbes within biofilms use molecular signal molecules to communicate [2] and are quite promiscuous - regularly exchanging genetic material among measures [3]. The material that forms biofilm matrixes is called extracellular polymeric substance - EPS. EPS is a complex mixture of polymeric molecules including, carbohydrates, deoxyribonucleic acid (DNA), lipids, lipopolysaccharides, and proteins. Once though to be a uniform mass, like a gelatinous coating, the EPS matrix is now known to be structurally complex. As illustrated in figure 1, the EPS matrix has channels trough which fluid can pass, zones that are nearly cell-free (thought to be used for nutrient storage), and zones in which microbial cells are densely packed. Biofilms release cells into the environment passively when outer layers are eroded away by fluid flow and actively when EPS bursts open to eject microbes (figure 2). Thus, biofilm communities are reservoirs for MWF recontamination, and - by extension - bioaerosols. Figure 1: Biofilm structure schematic. Figure 2: Biofilm consortium - active and passive planktonic cell release. 3. Biofilm Distribution in MWF Systems Although biofilms can grow on any wetted surfaces, they tend to be thickest at the MWF-sump wall-air interface and on surfaces on which MWF mist accumulates (i.e., splash zones) as shown in figures 3a and b. 92 23rd International Colloquium Tribology - January 2022 Do Biofilms in Metalworking Fluid Systems Matter? 4. Antimicrobial Pesticide Resistance Because the heaviest accumulations are not on surfaces that are in continuous contact with recirculating MWF, they are difficult to treat. Moreover, even when microbicides can be reliably brought into contact with biofilms, effective treatment typically requires 10x to 1000x the dose that is effective against planktonic (free-floating) cells [4]. Successful biofilm disinfection routinely requires repeated treatment as illustrated in figure 4. Figure 3: Biofilms on MWF system surfaces - a) sump wall at MWF-wall-air interface; b) on underside of a deck plate (sluice cover). Figure 4: Effect of repeated microbicide treatment on biofilm growth - a) Intact biofilm on MWF system surface; b) Initial dose kills exposed cells near EPS surface; c) 2nd dose further degrades EPS and kills additional cells; d) 3rd dose kills remaining cells and disinfects surface. 5. Conclusion Biofilms are complex EPS structures that provide a micro-environment in which microbial consortia can carry out activities that no single consortium member could. As units, they function like primordial, multi-cellular organisms. Because of their unique structural and functional properties, biofilms serve as reservoirs for both bioaerosols and recontamination of recirculating fluids. References [1] ASTM E2169-17, Standard Practice for Selecting Antimicrobial Pesticides for Use in Water-Miscible Metalworking Fluids, ASTM International, West Conshohocken, PA, 2017, www.astm.org, https: / / doi.org/ 10.1520/ E2169-17 [2] Lim, J., Lee, K-M, Park, C.Y., Kim, H.V., Kim, Y., and Park, S., “Quorum Sensing is Crucial to Escherichia coli O157: H7 Biofilm Formation under Static or Very Slow Laminar Flow Conditions”, BioChip J., 2016, 241-249, https: / / doi.org/ 10.1007/ s13206-016-0310-9 [3] Maunders, E., and Welch, M., “Matrix exopolysaccharides; the sticky side of biofilm formation”, FEMS Microbiol Let., 364, 13, 2017, 34 pp, https: / / doi.org/ 10.1093/ femsle/ fnx120 [4] Passman, F.J., and Küenzi, P., “Microbiology in Water-Miscible Metalworking Fluids”, Tribol. Trans., 63, 6, 2020, 1147-1171, https: / / doi.org/ 10. 1080/ 10402004.2020.1764684