ASTM E 3435 : 2024

1.1The Biofilm Surface Test Protocol (BSTP) is a high-throughput screening approach used to determine the antimicrobial activity of either liquid agents or agents impregnated, coated, or otherwise incorporated into a medical device or surface. This practice may also be used to evaluate surface-modified devices that contain no antimicrobial agent. A key feature of this practice is the growth and challenge of biofilms on a relevant surface of interest, as opposed to a predetermined material such as polystyrene (see, for instance, Test Method E2799).

1.2The BSTP incorporates key salient features to provide a simple, robust challenge of the device/surface while simulating the real-world environment to which the device will be exposed. This practice mimics the host environment (for example, by pre-conditioning the device/surface with a relevant medium, such as serum, artificial urine, or artificial mucous), the scope of organisms to which the device will be exposed (for example, clinical isolates), and the conformation of the device as it will be used and presented to the challenge organisms in a clinical or environmental setting (for example, if desired, testing can evaluate both the intraluminal and extraluminal surface of a catheter or be limited to the extraluminal surface). Variations of this assay have been correlated to in vivo models and human clinical trials (1-3).2 Corrosion, encrustation, or biofouling of devices or surfaces can also be evaluated using this practice.

1.3This practice is versatile and can be used for growing and evaluating biofilms of many different organisms, such as Pseudomonas aeruginosa, Klebsiella pneumoniae, Enterobacter aerogenes, Staphylococcus epidermidis, Staphylococcus aureus, Candida albicans, Enterococcus faecalis, Escherichia coli, Clavibacter michiganensis, Fusarium sp. Verticillium dahlia, and Botrytis cinerea (see Refs 4-8). Other examples from unpublished studies include Salmonella enterica, Proteus mirabilis, and Listeria monocytogenes. Appropriate modifications to the practice may be required when testing organisms not specified herein.

1.4Validation of disinfectant neutralization can be included as part of the assay.

1.5This practice describes how to sample a biofilm and quantify viable cells. Biofilm population density is recorded as log₁₀ colony forming units per device. To test for any antimicrobial activity due to leaching, suspended bacterial population density is reported as log₁₀ colony forming units per volume. Efficacy is reported as the log₁₀ reduction of viable cells. Alternatively, or additionally, qualitative or semi-quantitative assessments can be utilized, such as colorimetric staining, microscopy, or turbidimetric assessment of the minimal biofilm eradication concentration (MBEC; see Test Method E2799).

1.6This practice should be performed only by those trained in microbiological techniques.

1.7It is the responsibility of the investigator to determine whether Good Laboratory Practices (GLPs) are required and to follow them when appropriate.

1.8Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.9This 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.10This 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.