5.1 Vegetative biofilm bacteria are phenotypically different from suspended planktonic cells of the same genotype. Biofilm growth reactors are engineered to produce biofilms with specific characteristics. Altering either the engineered system or operating conditions will modify those characteristics. The goal in biofilm research and efficacy testing is to choose the growth reactor that generates the most relevant biofilm for the particular study.

5.2 The purpose of this test method is to direct a user in how to grow, treat, sample and analyze a Pseudomonas aeruginosa biofilm using the MBEC Assay. Microscopically, the biofilm is sheet-like with few architectural details as seen in Harrison et al (6). The MBEC Assay was originally designed as a rapid and reproducible assay for evaluating biofilm susceptibility to antibiotics (2). The engineering design allows for the simultaneous evaluation of multiple test conditions, making it an efficient method for screening multiple disinfectants or multiple concentrations of the same disinfectant. Additional efficiency is added by including the neutralizer controls within the assay device. The small well volume is advantageous for testing expensive disinfectants, or when only small volumes of the disinfectant are available.

1.1 This test method specifies the operational parameters required to grow and treat a Pseudomonas aeruginosa biofilm in a high throughput screening assay known as the MBEC (trademarked)2 (Minimum Biofilm Eradication Concentration) Physiology and Genetics Assay. The assay device consists of a plastic lid with ninety-six (96) pegs and a corresponding receiver plate with ninety-six (96) individual wells that have a maximum 200 μL working volume. Biofilm is established on the pegs under batch conditions (that is, no flow of nutrients into or out of an individual well) with gentle mixing. The established biofilm is transferred to a new receiver plate for disinfectant efficacy testing.3, 4 The reactor design allows for the simultaneous testing of multiple disinfectants or one disinfectant with multiple concentrations, and replicate samples, making the assay an efficient screening tool.

1.2 This test method defines the specific operational parameters necessary for growing a Pseudomonas aeruginosa biofilm, although the device is versatile and has been used for growing, evaluating and/or studying biofilms of different species as seen in Refs (1-4).5

1.3 Validation of disinfectant neutralization is included as part of the assay.

1.4 This test method describes how to sample the biofilm and quantify viable cells. Biofilm population density is recorded as log₁₀ colony forming units per surface area. Efficacy is reported as the log₁₀ reduction of viable cells.

1.5 Basic microbiology training is required to perform this assay.

1.6 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.7 ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentioned in this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the risk of infringement of such rights, are entirely their own responsibility.

1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.