# The Effect of Human Blood Plasma Conditioning Films on Platelet Tungsten Bag Surface Properties
## 1 Introduction  
Bacterial contamination of blood products poses one of the biggest risks of transfusion medicine [1]. This contamination is most commonly associated with the transfusion of platelet concentrates (PC) due to their storage conditions within the blood bank, providing ideal conditions for bacterial growth and proliferation. It is reported that approximately 1 in 2000-5000 PCs are contaminated with bacterial species [2, 3, 4]. Although bacteria can, and do, exist in a planktonic state (single cells suspended in medium) the majority of species implicated in PC contamination possess the ability to form biofilms within the transfusion bag [5]. This occurs since bacteria preferentially adhere to a surface. Once large numbers of bacteria become attached and retained to a surface, a biofilm is formed. It has been suggested that once in a biofilm, bacterial metabolism is slowed [6]. This hampers the ability of bacterial detection systems that rely on threshold levels of CO\({}_{2}\) being produced to detect bacterial contamination pre-transfusion. It is widely accepted that the physical and chemical properties of a surface will have a significant influence on the ability of bacterial species to form biofilms [7]. It has been well established that once a surface becomes exposed to an environment, it immediately starts to adsorb a conditioning film (CF) and thus becomes fouiled [8]. Whilst surface properties massively influence bacterial adhesion, bacterial cells often do not attach to the surface directly but instead attach to an interface of the surface which has been exposed to its surrounding environment and 'conditioned' [9]. This CF acts as a layer between thesurface itself and the environment, altering how the surface interface interacts with external materials [10]. Indeed, a CF on a surface can mask the underlying features of the surface and alter the ability of bacteria to be retained, with the adsorbed molecules potentially stimulating or decreasing bacterial attachment [11]. However, the nature of the CF can vary significantly depending upon the conditions of the surrounding environment [12]. For example, environmental CFs can be formed on surfaces exposed to seawater as described by [PERSON] and [PERSON] (2009) [8], but can also be formed by bodily fluids (such as blood, tears, saliva and urine) on biomaterials [12]. When considering the attachment of bacteria and the formation of biofilms onto platelet bag surfaces, it is important to understand the type of CF and how this adsorption to the surface affects the surface properties in terms of the topography, chemistry and physicochemistry [13]. The adsorption of a CF has been demonstrated to affect the degree of bacterial attachment [14]. The addition of human plasma to media has been shown to increase _Staphylococcus aureus_ biofilm formation and affect the biofilm phenotype and cell morphology [15]. However, in another study, it was demonstrated that human serum components had anti-biofilm effects on _S. epidermidis_ biofilms, but did not affect established biofilms [16]. Further, a study has demonstrated that conditioning surfaces with adsorbed fibronectin, a protein abundant in blood plasma, reduced the adhesion of _S. epidermidis_ to a surface, but this was dependent upon the amount of adsorbed fibronectin [17]. These studies demonstrate the complexity of conditioned surfaces and how they can significantly alter the interactions between the bacteria and a substrate. _S. epidermidis_ and _Serratia marcescens_ are regularly identified as bacterial contaminants isolated from contaminated PCs. _S. epidermidis_ is highly implicated in platelet contamination, probably due to being abundant as part of normal human skin flora [18; 19]. _Ser. marcescens_ has only been considered as an opportunistic pathogen over the last 30 years [20]. It is likely that the abundance of _Ser. marcescens_ in the environment has resulted in it being identified as a major PC contaminant [21].