Abstract
The antimicrobial effect of cationic silver has been well established; however evidence of bacteria interactions with antimicrobials has seen limited investigation. This study aimed to investigate the growth and attachment behaviour of resident human skin bacterial strains on an antimicrobial silver fabric. A silver treated textile was supplied by a New Zealand apparel company.
The antimicrobial effect of the silver treated textile was investigated in two parts. Firstly the efficacy of the antimicrobial was tested against a selection of known residential human skin bacterial strains. Secondly the bacterial growth behaviour of the bacterial strains on fabric was examined against the silver treated textile (nonwashed and washed), alongside a woven and knit control of similar structural fabric properties. A novel humidity chamber was designed that enabled the fabrics to be suspended in a controlled environment where the temperature and humidity simulated that of the microclimate at the skin surface. Fabrics were inoculated with bacteria and suspended in the chamber for varying lengths of time that coincide with normal wear of clothing. Bacterial cells were removed from the fabrics and grown over 24 hours in order to quantify bacterial growth on the fabrics. Growth was represented as a percentage of the colonies originally inoculated on the fabric in attempts to quantify bacterial adherence.
The silver treated fabric sold and marketed for antimicrobial purposes was shown not to exhibit any bactericidal effect using the methods set out in this study, regardless of the selected bacterial strain or concentration of bacterial populations. The bacterial activity of the strains on the fabrics did not produce results that were expected. Due to the absence of an antimicrobial effect, the activity of the natural skin bacterial strains on the fabric did not reduce with the addition of the “antimicrobial” treatment. In some cases bacterial activity was increased with the addition of the antimicrobial treatment. Although washing the antimicrobial fabric resulted in a tighter sett, there was no change in bacterial activity. Gram positive and gram negative cell membrane structure differences did not influence bacterial interaction with the fabrics. Anaerobic bacteria did not display fabric interaction until after 6 hours as opposed to one hour for the aerobic bacterial strains. In general the longer the fabric was exposed to the simulated wear environment, the more bacteria grew and the greater the interaction with the fabric. Overall, fabric structure had no affect on bacterial interaction. Majority of the differences recorded in this study were in the order of one log or less which is minimal in terms of bacterial growth.
There is an issue in the textile sector of antimicrobials being marketed as such, with limited proof of bactericidal effect. Although the issue regarding bacterial interactions on antimicrobials still stands, this study brings to light the challenges faced by apparel companies reliant on fabric suppliers. There is the need for transparency in supply chains and standardised international requirements for demonstrating antimicrobial efficacy of antimicrobials. Antimicrobial resistance is an international concern. Manufacturers and consumers need to take care in the use of antimicrobials.