ORIGINAL ARTICLE A long-term study examining the antibacterial effectiveness of Agion silver zeolite technology on door handles within a college campus B.A. Potter 1 , M. Lob 1 , R. Mercaldo 1 , A. Hetzler 1 , V. Kaistha 1 , H. Khan 1 , N. Kingston 1 , M. Knoll 1 , B. Maloy-Franklin 1 , K. Melvin 1 , P. Ruiz-Pelet 1 , N. Ozsoy 1 , E. Schmitt 1 , L. Wheeler 1 , M. Potter 2 , M.A. Rutter 3 , G. Yahn 4 and D.H. Parente 5 1 Department of Biology, Penn State Erie, The Behrend College, Erie, PA, USA 2 RJ Lee Group, Monroeville, PA, USA 3 Department of Mathematics, Penn State Erie, The Behrend College, Erie, PA, USA 4 Advanced Finishing USA, Fairview, PA, USA 5 Sam and Irene Black School of Business, Penn State Erie, The Behrend College, Erie, PA, USA Significance and Impact of the Study: There has been a dramatic increase in the use of silver-containing antimicrobials within the medical and consumer markets despite many concerns on how increased usage will impact the environment. To begin addressing these concerns, it is important to first deter- mine whether the silver-containing antimicrobials are significantly affecting bacterial populations out- side of the controlled laboratory setting. A significant decrease was seen in this study examining the effectiveness of Agion silver zeolite technology applied to door handles across a college campus. Results showed the recovery of a bacterial population on silver-coated door handles suggesting a bias in the effectiveness of this technology. Keywords antibacterial effect, bacteria, culture dependent, silver ions, silver zeolite. Correspondence Beth A. Potter, Penn State Erie, The Behrend College, 4205 College Drive, Erie, PA 16563, USA. E-mail: bap16@psu.edu 2014/1332: received 30 June, 2014, revised 2 October, 2014 and accepted 24 October, 2014 doi:10.1111/lam.12356 Abstract Laboratory studies have shown that small concentrations of silver are effective at inhibiting the growth micro-organisms through the disruption of important cell structures and processes. The additional ability to incorporate silver into surfaces has increased the usage of silver in the medical field and expanded its use into the consumer market. To understand the impact of increased silver- containing antimicrobial use, it is important to determine whether silver-based consumer goods are effective at reducing bacterial populations. Our study examined the antibacterial effectiveness of Agion silver zeolite technology applied to 25 silver- and control-coated door handles across a college campus. Door handles were sampled for 6 week periods in both the fall and spring semester, and bacteria were cultured and enumerated on tryptic soy agar (TSA), MacConkey agar (MAC) and mannitol salt agar (MSA). A significant difference was observed between the bacterial populations isolated from silver- and control-coated door handles after 3 years. However, bacteria were consistently isolated from silver-coated door handles suggesting that the silver zeolite was only effective against a portion of the bacterial populations, and further studies are necessary to determine the identities of the isolated bacteria and the prevalence of silver resistance. Introduction Silver is one of the oldest antimicrobial agents, used by the ancient Egyptians and Romans to preserve liquids and foods (Franke 2007; Silvestry-Rodriguez et al. 2007). Solid silver nitrate formally entered the medical field in the Middle Ages as a treatment for chronic wounds and ulcers (Klasen 2000). By the end of the 19th century, Letters in Applied Microbiology 60, 120--127 © 2014 The Society for Applied Microbiology 120 Letters in Applied Microbiology ISSN 0266-8254