Significance and Use
5.1 Vegetative biofilm bacteria are phenotypically different from suspended planktonic cells of the same genotype (9). Biofilm is the etiological agent of many implant and device-related infections and, once established, microorganisms in biofilm can be up to 1000 times more tolerant to antibiotic therapy.
5.2 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 a particular study (10). Common systems used to grow biofilms in laboratories include flow cells, drip flow reactors, spinning-disk reactors, and tube biofilm reactors. These specialized models have several advantages, including growth of biofilms to high population densities and controlled fluid dynamics. The purpose of this practice is to direct a user in how to grow, treat, sample, and analyze a biofilm on the surface of virtually any medical device or material of interest, using the more simplistic BSTP.
5.3 The BSTP was originally designed as a rapid and reproducible assay for evaluating biofilm growth on surfaces (9 and 11). The design allows for the simultaneous evaluation of multiple parameters—such as testing multiple disinfectants or multiple concentrations of the same disinfectant, testing multiple surfaces (for example, coated versus uncoated), multiple challenge organisms, various growth media, growth/challenge times, and so on—making it an efficient screening tool. In addition to the throughput afforded by the use of a multi-well plate, the BSTP allows for extremely facile rinses, media changes, challenges, and recovery steps by virtue of immobilizing the test devices/surfaces to the lid of the multi-well plate. Moreover, the BSTP requires no specialized reactors or equipment and, as it does not depend upon continuous flow, uses relatively small volumes of media and other reagents.
Scope
1.1 The 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).
1.2 The 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.
1.3 This 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.
1.4 Validation of disinfectant neutralization can be included as part of the assay.
1.5 This 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).
1.6 This practice should be performed only by those trained in microbiological techniques.
1.7 It is the responsibility of the investigator to determine whether Good Laboratory Practices (GLPs) are required and to follow them when appropriate.
1.8 Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.9 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.10 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.
