A novel comprehensive efficacy test for textiles intended for use in the healthcare setting
Introduction
Soft surfaces are found abundantly in the healthcare setting ranging from healthcare worker attire and wound dressings, to bed linens, privacy curtains, and upholstered furniture (Adlhart et al., 2018; Ahonen et al., 2017; Dunne et al., 2017; Koca et al., 2012; Mitchell et al., 2015). Similar to hard surfaces, soft surfaces risk becoming contaminated with pathogenic microorganisms (Burden et al., 2011; Burden et al., 2013; Du et al., 2017; Sanon and Watkins, 2012; Sattar et al., 2001; Treakle et al., 2009; Wiener-Well et al., 2011). Due to their large surface area and porous nature, soft surfaces are prone to microbial growth and biofilm development, particularly in the presence of appropriate nutrient, temperature, and moisture levels. Numerous studies have demonstrated the persistence of pathogens on hospital textiles, some of which can survive on soft surfaces for months) (Kramer et al., 2006; Lopez-Gigosos et al., 2014). Additionally, bacteria can be transferred from contaminated textiles to human skin, especially when the fabrics are moist (Sattar et al., 2001).
Because of the growing public health awareness of soft surface contamination, particularly in the healthcare setting, extensive research and development have been devoted to the generation of textiles hostile to microbial growth. Antimicrobial textiles are an effective strategy for reducing the bioburden on soft surfaces (Adlhart et al., 2018; Ahonen et al., 2017; Lopez-Gigosos et al., 2014; Morais et al., 2016; Santos et al., 2016; Sun et al., 2012; Treakle et al., 2009; Wiener-Well et al., 2011). Use of antimicrobial textiles as an engineering control in the healthcare setting has been proposed to mitigate the cross-contamination and spread of healthcare-associated infections (HAIs). Antimicrobial agents can either be incorporated into materials or grafted to fabric surface as a finishing agent after assembly of the basic fabric (Adlhart et al., 2018; Burden et al., 2013; Koca et al., 2012; Kramer et al., 2006; Mitchell et al., 2015; Sanon and Watkins, 2012; Sattar et al., 2001). To maximize benefit, the antimicrobial finishing should be effective against a broad range of microorganisms with low toxicity to the user and the environment. Additionally, the antimicrobial finishing should be durable throughout its service life, and be able to endure laundering, drying, and day-to-day use. Lastly, antimicrobial finishes should ideally not impair the textile appearance or texture (Morais et al., 2016). Numerous antimicrobial textiles are currently available, each of which differs in the mode of action of their microbial components (Table 1).
One of the most interesting antimicrobial approaches, and the textile used in this study, is the rechargeable N-halamine based fabric. The characteristics of this fabric have been previously published in detail (Luo and Sun, 2006). In brief, N-halamines are compounds containing one or more nitrogen-halogen bonds, which demonstrate a broad spectrum of biocidal activity. The antimicrobial properties of N-halamines are based on the exchange of halogen (commonly chlorine) atoms with microorganisms in the presence of water. The N-halamine-based fabric possesses several desirable characteristics suitable for application in the healthcare setting (Adlhart et al., 2018; Ahonen et al., 2017; Luo and Sun, 2006). N-halamine textiles: 1) are highly stable for a long period of time in ambient temperatures, 2) have a low dissociation constant, which makes the N-halamine much more stable and safer for human use than free chlorine or bleach, 3) are compatible with nylon, polyester, acrylics, and cotton-cellulose, 4) can be synthesized with specific concentrations (%) of N-halamine, 5) have the ability to be regenerated or recharged with a diluted bleach rinse after the halogen functional groups have been consumed, and 6) are monitorable for antimicrobial action (active chlorine components).
Effective testing is the key to understanding the performance of antimicrobial textiles. There are several published standards for assessing antimicrobial efficacy that include both qualitative (absorption or halo-methods) and quantitative methods (see Table 2). While the existing standards can be utilized to assess antimicrobial activity of individual textiles, they have different testing parameters and procedures. The lack of standardization and differences between each method analyzing antimicrobial activity makes meaningful comparison between the performance of different fabrics challenging (Pinho et al., 2011). The purported antimicrobial activity of one fabric determined by one method cannot readily be compared to antimicrobial activity determined by a different method. Furthermore, there exists limited data comparing the performance of distinct antimicrobial textiles in real-world scenarios.
Currently the most commonly applied standards in the U.S are the qualitative American Association of Textile Chemists and Colorists AATCC 147:2019 “Assessment of Textile Materials: Parallel Streak Method” and the quantitative AATCC 100:2011(2016e) “Antibacterial Finishes on Textile Materials: Assessment of” (AATCC, 2016; AATCC, 2019). Both standards specify testing against pure cultures of Staphylococcus aureus and Klebsiella pneumoniae as representative Gram-positive and Gram-negative pathogens. Additional microorganisms may be included at the discretion of the testing party, but are not mandated. Additionally, the standards do not define pass-fail criteria, ultimately allowing the manufacturer or testing party to determine its own antimicrobial success. The AATCC 147 method is easily reproducible and relatively easy to perform, and provides qualitative data on the fabric's bacteriostatic capabilities. The AATCC 100 is a quantitative method, but it does not specify the final concentration of bacteria to be tested (the protocol states adjust to ‘appropriate dilution’). In addition, the test swatches utilized must be able to absorb 1 mL of liquid, therefore more than one fabric swatch (comparable to plies of fabric) are commonly utilized since a single swatch usually cannot absorb the full volume, even if the proposed use of the textile would be single ply.
Standardized in-lab qualitative and quantitative tests are an essential first step in evaluating the antimicrobial activity of a fabric. However, for textiles intended for use in healthcare, there are several aspects of real-world application that are not reflected in these protocols. Antimicrobial textiles can be marketed and utilized in the healthcare setting without accompanying data validating the performance of the textile under actual use conditions. We hypothesized that a novel, more comprehensive, efficacy test for antimicrobial healthcare textiles could be used to evaluate a textile's performance in the presence of: 1) pure cultures of important HAI-causing microbes and normal skin microorganisms, 2) reproducible mixtures of skin microorganisms with pathogens, and 3) artificial soils, including artificial sweat and 5% serum. We also hypothesized that the N-halamine fabric would effectively reduce microorganism contamination under the conditions tested. Our protocol builds on the existing methods to provide a broader and more realistic characterization of the antimicrobial efficacy of fabrics intended for use in healthcare.
Section snippets
Bacterial strains and materials
All bacterial strains were purchased from the American Type Culture Collection (ATCC, Manassas VA). Lyophilized samples were rehydrated and cultured onto appropriate media and subcultured at least 3 times before use. Pathogens included: Acinetobacter baumannii (ATCC 19606), Candida albicans (ATCC 24433), Escherichia coli (ATCC 29214), vancomycin-resistant Enterococcus faecalis (ATCC 51575), methicillin-resistant Staphylococcus aureus (ATCC 43300), methicillin-susceptible Staphylococcus aureus
Microorganism growth and reproducibility in the test procedure
The testing protocol was successful in producing both adequate colony growth of all single and mixtures of microorganisms and the soils had no impact on the growth of the microorganisms. For single microorganism trials, the procedure consistently generated growth of every microorganism attempted. Each trial was performed in duplicate and quantity of growth was consistent between associated pairs of plates. For trials that involved mixtures of microorganisms, the procedure consistently generated
Discussion
Despite improved hygiene practices and dynamic infection prevention programs, the transmission of microorganisms in the healthcare setting remains of great concern. It is well documented that soft surfaces in the healthcare setting, particularly fabric, are contaminated with pathogens, and therefore play a role in the chain of infection, including the transfer of microbes from fabric to human skin (Boutin et al., 2014; Koca et al., 2012; Lopez-Gigosos et al., 2014; Nordstrom et al., 2012; Scott
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
This work was supported by Grant number 1 R21OH011406-01A1, funded by the National Institute of Occupational Safety and Health, Centers for Disease Control and Prevention. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the Centers for Disease Control and Prevention or the Department of Health and Human Services.
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Present Address: Samantha Queiroz, Instrumentation Laboratory, A Werfen Company, Bedford MA, 01730, USA.