Biofilm, self-organized communities of bacteria that can have both positive and negative effects in a variety of industries, is the subject of a new ASTM International standard, E 2562, Test Method for Quantification of Pseudomonas aeruginosa Biofilm Grown with High Shear and Continuous Flow Using CDC Biofilm Reactor. The new standard is under the jurisdiction of Subcommittee E35.15 on Antimicrobial Agents, which is part of ASTM International Committee E35 on Pesticides and Alternative Control Agents.
Confocol image of the biofilm that is grown in the CDC biofilm reactor.
According to Darla Goeres, senior research engineer, Center for Biofilm Engineering, biofilm consists of bacteria attached to a surface that are embedded in a layer of slime. Bacteria in the biofilm secrete a plastic-like substance called extracellular polysaccharides, which forms the protective slime layer around the cells and binds them together. In addition to bacteria, the slime layer may contain anything from corrosion products and scale to blood and dead skin cells, depending on the environment in which the biofilm forms.
“Historically, scientists believed that the bacteria attached to the surface randomly,” says Goeres. “We now understand that biofilm is a dynamic, organized cooperative community of bacteria. The bacteria communicate through chemical signaling and this allows them to attach and detach in an organized pattern beneficial to the biofilm. Fundamental research has shown that biofilm bacteria are different from free-floating, individual bacteria that have been the focus of most antibacterial efficacy testing up to this point.”
Biofilm corrodes pipes in oil reservoirs and is a cause of infection associated with medical devices such as catheters. In addition, biofilm harbors pathogenic bacteria such as Legionella (the cause of Legionnaire’s disease) in cooling systems and hot tub filters.
However, as Goeres points out, there are positive uses for biofilm as well. “For example, biofilm may bioremediate gasoline leaking from an underground storage tank or the acid drainage associated with mine tailing ponds,” says Goeres. “Right now, industry, medical, professional and regulatory agencies are learning about biofilms and how to best control them and exploit them.”
Biofilm efficacy testing is a four-step process:
1. Grow a relevant and repeatable biofilm in a laboratory reactor;
2. Treat a mature biofilm with biocide or antibiotics;
3. Sample the biofilm, which includes removing it from the surface and disaggregating the clumps; and
4. Analyze the sample for quantitative and/or qualitative estimate of kill and/or removal as a result of the treatment.
Interested parties are invited to join the standards developing activities of Subcommittee E35.15, which will eventually include proposed low shear and no shear biofilm growth protocols and treatment protocols. “Biofilm research is truly an interdisciplinary field that draws upon fundamental principles in engineering, microbiology, biochemistry, statistics and mathematics,” says Goeres.
Darla Goeres, Center for Biofilm Engineering, Bozeman, Mont.
Oct. 29-Nov. 1
October Committee Week