g. [4, 13–16]). This study utilizes an engineering approach, known as robustness analysis, which is used to analyze complex systems. Robustness analysis determines the stability of a system response to perturbations. Robust systems return similar or identical responses when perturbed

while non-robust systems return very different responses [17, 18]. Biofilm antibiotic tolerance is a product of complex cellular systems. The presented study examines the robustness of colony biofilm antibiotic tolerance to industrially and medically relevant perturbations including 1) nutrient environment 2) temperature 3) quorum sensing ability and 4) growth phase. To our knowledge, this is the first time robustness analysis has been applied to biofilm antibiotic tolerance. Antibiotic tolerance is at the heart of many practical challenges related to unwanted biofilms. Being able to predict biofilm antibiotic tolerance learn more as a function of culturing perturbations is essential for rationally designing and evaluating antimicrobial strategies. The presented results shed insight on the varying success rates of common

anti-fouling strategies like antibiotic impregnated coatings and provide a template for improved antimicrobial testing schemes. Results 1. Antibiotic tolerance in planktonic and biofilm cultures Biofilms often exhibit very different antibiotic tolerances than planktonic cultures [1–4]. To interpret the presented biofilm data in an appropriate context, the antibiotic tolerances Selleckchem Ku 0059436 of biofilm

cultures were compared to planktonic cultures. Antibiotics representing the aminoglycoside and beta-lactam classes were used as proxies for the diverse array of utilized agents. Kanamycin and ampicillin tolerances were determined for planktonic and Casein kinase 1 biofilm cultures grown in Luria-Bertani (LB) medium at 37°C. These antibiotics were highly effective against planktonic cultures reducing colony forming units (cfu’s)/ml by 6 to 9 orders of magnitude (Fig. 1a). The biofilm antibiotic tolerance results were varied. Kanamycin produced a 9 log10 reduction in cfu’s per biofilm while ampicillin resulted in only a one log10 reduction in cfu’s per biofilm (Fig 1b). Subsequent biofilm responses to culturing perturbations were compared to these base tolerance results (Fig. 1b). Just prior to antibiotic challenge, the biofilm cultures contained 9.3 log10 ± 0.1 cfu’s/biofilm while the planktonic cultures had 7.8 ± 0.2 log10 cfu’s/ml. Additional data illustrating differences in colony biofilm antibiotic susceptibility as compared to planktonic cultures can be found in Additional file 1, Figs. S1 and S5. Figure 1 Comparison of planktonic and biofilm antibiotic tolerance. Wild-type E. coli K-12 cultures were grown on LB only medium at 37°C. Cultures were grown for 6 hours before being transferred to fresh antibiotic treatment medium for 24 hours.