Physicochemical regulation of biofilm formation

Abstract

This article reviews the physical and chemical constraints of environments on biofilm formation. We provide a perspective on how materials science and engineering can address fundamental questions and unmet technological challenges in this area of microbiology, such as biofilm prevention. Specifically, we discuss three factors that impact the development and organization of bacterial communities. (1) Physical properties of surfaces regulate cell attachment and physiology and affect early stages of biofilm formation. (2) Chemical properties influence the adhesion of cells to surfaces and their development into biofilms and communities. (3) Chemical communication between cells attenuates growth and influences the organization of communities. Mechanisms of spatial and temporal confinement control the dimensions of communities and the diffusion path length for chemical communication between biofilms, which, in turn, influences biofilm phenotypes. Armed with a detailed understanding of biofilm formation, researchers are applying the tools and techniques of materials science and engineering to revolutionize the study and control of bacterial communities growing at interfaces.

Figure 1

Parameters that influence the interactions between bacteria and surfaces. The cell wall of Gram-positive bacteria consists of an inner lipid membrane surrounded by a layer of cross-linked polysaccharide referred to as the peptidoglycan. The cell wall of Gram-negative bacteria consists of an inner lipid membrane surrounded by a layer of peptidoglycan, which is surrounded by an outer lipid membrane. Outer membrane proteins and lipopolysaccharide provide surface charge. Some bacteria have a capsule that extends beyond the cell wall and consists of a thick layer of alginate and other complex polysaccharides. Extracellular organelles for attachment and motility include pili, curli, fimbriae, and flagella. The surface of substrates has intrinsic charge from functional groups that are solvent exposed. The composition of the surrounding environment also influences the interactions during bacterial cell attachment.

Figure 2

The initial attachment of bacteria to substrate surfaces is characterized by electrostatic repulsion or attraction. Once this obstacle is overcome, hydrophobic interactions influence the attachment of bacteria to surfaces. This binding event initiates the genetic regulation and expression and secretion of chemical factors such as quorum sensing molecules to induce biofilm formation and expression of extracellular polymeric substance. The design of specific substrate topography can influence the initial attachment of bacterial cells and regulate biofilm formation.

Figure 3

Comparison of P. aeruginosa adhesion on topographically patterned and non-patterned surfaces. (a)The image shows the adhesion of cells to a flat region of an epoxy substrate (top left) and to a topographically patterned epoxy substrate (bottom left). (b–c) Cross-sectional scanning electron microscopy images of cells cultured on flat and topographically patterned epoxy surfaces, respectively, showing the difference in attachment morphology. Scale bars are 10 μm in (a) and 1 μm in (b) and (c). Reproduced with permission from Reference . ©2010, American Chemical Society.

Figure 4

Representative scanning electron microscopy images of Staphylococcus aureus on polydimethylsiloxane (PDMS) surfaces over the course of 21 days (areas of bacteria highlighted with color to enhance contrast). On the left are smooth PDMS surfaces, and the right column shows Sharklet AF PDMS surfaces. (a) and (b) Day 0, (c) and (d) Day 2, (e) and (f) Day 7, (g) and (h) Day 14, and (i) and (j) Day 21. The patterned surface decreases the number of attached cells significantly. Reproduced with permission from Reference . ©2007, AVS Science & Technology of Materials, Interfaces, and Processing.

Figure 5

(a–d) Scanning electron microscopy (SEM) images of S. aureus and E. coli K12 in contact with bare silicon wafers (a and b, respectively) and on silicon wafers coated with N,N′-dodecyl-methyl-PEI (c and d, respectively); PEI, poly(ethyleneimine). The scale bars are 1 μm. (e) A plot depicting the effect of the N,N′-dodecyl-methyl-PEI coating on the viability of E. coli K12 and on the concentration of intracellular proteins released into solution via cell lysis. The shaded bars represent bactericidal efficiencies; error bars were omitted for clarity. Total protein in solution after incubation with plain (empty square) and N,N′-dodecyl-methyl-PEI-coated (filled square) polypropylene tubes are shown with lines. Reproduced with permission from Reference . ©2011, Springer.