Metal surface characteristics dictate bacterial adhesion capacity Klemen Bohinc a,n , Goran Dražić b,d,f , Anže Abram b,f , Mojca Jevšnik a , Barbara Jeršek c , Damijan Nipič a , Marija Kurinčič c , Peter Raspor c,e a Faculty of Health Sciences, Zdravstvena pot 5, 1000 Ljubljana, Slovenia b Jožef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia c Biotechnical Faculty, Jamnikarjeva 101,1000 Ljubljana, Slovenia d National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia e University of Primorska, Faculty of Health Sciences, Head of the Institute for Food, Nutrition and Health, Polje 42, 6310 Izola, Slovenia f Jožef Stefan International Postgraduate School, Jamova cesta 39, 1000 Ljubljana, Slovenia article info Article history: Received 5 August 2014 Accepted 26 January 2016 Available online 1 February 2016 Keywords: Bacterial adhesion Metal surfaces Roughness abstract Bacterial adhesion can be dictated by different surface characteristics. In this study we concentrate on the surface roughness of a stainless steel material. We prepared the stainless steel surfaces by 3D polishing, brushing, grinding and electropolishing. Untreated stainless steel surfaces were also considered. The corresponding surface roughness was assessed by profilometry and atomic force microscopy. In experiments we have used different types of bacteria. The rate of adhered bacteria on metal surfaces was determined spectrophotometrically. The results showed that the rate of adhered bacteria increases with increasing surface roughness. Scanning electron microscopy was used to image surfaces in order to determine locations of adhered bacteria. The increased adhesion of bacteria on more rough surfaces results from an increased interplay between the increasing effective surface area and increasing numbers of cracks, voids and gaps. & 2016 Elsevier Ltd. All rights reserved. 1. Introduction Microbial contamination of different contact surfaces which has implications for human health and the environment creates major problems in different technologies like food, pharmacy and various service industries. By understanding the relationship between surface conditions and microbial adhesion, strategies can be developed to inhibit the attachment of bacteria and spores [1– 5]. Bacterial adhesion to a material surface is a complicated pro- cess that is affected by various physico-chemical properties of the bacteria cell and substratum surface [6]. The physicochemical properties of surfaces are governed by factors such as environment (temperature and pH), surface characteristics such as hydro- phobicity and charge and, in the case of a micro-organism hydrophobicity, flagellation and motility [1]. The basic stages of bacterial adhesion are generally described by a two-stage kinetic binding model. In a first stage there is an initial, rapid and easily reversible interaction between the bacteria cell surface and the material surface. The adhesion of bacteria within an interface is mainly governed by electrostatic, van der Waals, and hydrophobic effects and contact interactions [7,8]. Generally, the interaction free energy of the adhesion process shows two minima. The first minimum appears at a separation of 10 nm and is few kT (thermal energy, T is the absolute temperature and k is the Boltzmann constant). In this minimum the microorganism is weakly and reversibly bound. The second stage includes specific and non- specific interactions between so-called adhesion proteins expres- sed on bacterial surface structures (fimbriae or pili) and binding molecules on the material surfaces. The second minimum in the interaction free energy appears at a contact distances of 1 nm. Here the microorganism is strongly and irreversibly adhered. The microorganism has to surpass a large energy barrier of a few kT to overcome from the first into the second minimum at the contact point. The characterization of the surface topography of the material on a submicrometer scale can be obtained with atomic force microscopy [9]. In general, bacterial adhesion is a complicated process influ- enced by many factors. Boulané-Petermann [10] represents two physico-chemical theories that can be applied to predict simple cases of bacterial adhesion. However, these models are limited in their applicability owing to the complexity of bacterial surfaces and the surrounding medium. Various factors that can affect the bacterial adhesion process have been listed, all directly linked to the solid substratum, the suspension liquid or the microorganism (e.g. for stainless steel surfaces, it is important to take into account Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ijadhadh International Journal of Adhesion & Adhesives http://dx.doi.org/10.1016/j.ijadhadh.2016.01.008 0143-7496/& 2016 Elsevier Ltd. All rights reserved. n Corresponding author. E-mail addresses: klemen.bohinc@zf.uni-lj.si (K. Bohinc), peter.raspor@fvz.upr.si (P. Raspor). International Journal of Adhesion & Adhesives 68 (2016) 39–46