Synthesis and Activity of Biomimetic Bio fi lm Disruptors

Content Provider	Semantic Scholar
Author	Böttcher, Thomas Kolodkin-Gal, Ilana Kolter, Roberto Losick, Richard Clardy, Jon
Copyright Year	2013
Abstract	Biofilms are often associated with human bacterial infections, and the natural tolerance of biofilms to antibiotics challenges treatment. Compounds with antibiofilm activity could become useful adjuncts to antibiotic therapy. We used norspermidine, a natural trigger for biofilm disassembly in the developmental cycle of Bacillus subtilis, to develop guanidine and biguanide compounds with up to 20-fold increased potency in preventing biofilm formation and breaking down existing biofilms. These compounds also were active against pathogenic Staphylococcus aureus. An integrated approach involving structure−activity relationships, protonation constants, and crystal structure data on a focused synthetic library revealed that precise spacing of positively charged groups and the total charge at physiological pH distinguish potent biofilm inhibitors. M bacteria form biofilms, which are multicellular microbial communities embedded in a self-produced exopolymeric substance (EPS) largely composed of a protein anchor and different extracellular polymers. Bacteria within a mature biofilm community exist in an altered metabolic state and different physical environment than their free-floating, or planktonic, relatives. Biofilm bacteria generally tolerate antibiotic treatment, and antibiotics can induce biofilm formation. Consequently, biofilm inhibitors can be applied to decrease antibiotic tolerance of bacteria. Biofilms play a major role in many bacterial infections. In humans, the antibiotic tolerance of biofilm communities frustrates the treatment of persistent bacterial infections such as those associated with cystic fibrosis, endocarditis, joint prostheses, heart catheters, and replacement heart valves. In response to this challenge, high-throughput assays have been developed to identify small molecules with the ability to prevent biofilm formation or disrupt existing biofilms. We recently explored an alternative strategy that exploits the normal developmental cycle of bacteria. Biofilms form when planktonic bacteria in the aqueous phase aggregate on a solid surface or at an air−liquid interface. The biofilm colony grows both by recruitment and cell division to form a mature colony. Mature colonies eventually disintegrate, and the dispersed bacteria resume a planktonic lifestyle (Figure 1). Bacterially produced small molecules orchestrate the creation and disintegration of biofilms, and identifying these molecular signals could lead to therapeutically useful templates. We previously identified D-amino acids as potent biofilm disruptors because of their ability to release the protein component of EPS from the bacterial cell wall. Recently we identified norspermidine as a key disruptor of the polymeric component of EPS. Mixtures of norspermidine with D-amino acids were found to be highly synergistic (single-digit nanomolar) in disrupting biofilms (Figure 1). Here we report synthetic mimics of norspermidine with increased potency and a structure-based rationale for their activity. Norspermidine appears to disrupt biofilms by targeting the extracellular component of EPS in Bacillus subtilis, and it seemed likely that it does so by binding to negatively charged or possibly neutral groups using Coulombic attraction and hydrogen bonding as important features. We tested a set of commercially available polyamines. Norspermidine was most active in inhibiting biofilms for B. subtilis and Staphylococcus aureus, followed by norspermine, which has an additional aminopropyl unit in its structure [Figure S1 and Table S2 in the Supporting Information (SI)]. Perhaps surprisingly, spermidine, with one longer aminobutyl residue in place of an aminopropyl unit, and diethylenetriamine, with two shorter aminoethyl groups, were inactive in both species. This sharp length dependence indicated that matching the NH-to-NH distance of the (poly)propyleneamine motif of norspermidine and norspermine (4.9 Å) to the pitch of various helical EPS Received: December 11, 2012 Published: February 13, 2013 Figure 1. Stages in the developmental cycle of biofilm formation and disruption. Norspermidine both prevents the formation of new biofilms and collapses the structure of existing biofilms. Communication
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Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Article