A new method using laser trapping was established to understand how the spatial arrangements of microbes in a biofilm affects the course of chronic biofilm infections. This method was published in Biomedical Optics & Medical Imaging by Chris Rodesney from Dr. Vernita D. Gordon’s group from the Department of Physics at The University of Texas at Austin.
Biofilms are microbial communities of unicellular organisms that interact with each other and adhere to a surface. Normally, in natural environments, bacteria are organized in a biofilm. The biofilms have a negative impact in industry causing biofouling and biocorrosion, and in clinics by contaminating devices and infecting patients. The biofilm protects the bacteria against its removal and enable them to continue affecting the host. A better understanding of the properties of biofilms will enable the identification of targets for diagnostics and treatment of bacterial infections. The way bacterial spatial organization affects the course of biofilm infections is poorly understood mainly due to the limited available experimental strategies to produce typical biofilms that mimic the natural infections.
In this study, the research team established a method to organize and structure these bacterial systems with a resolution at single-cell level without changing the surface adhesion and motility of the bacteria. For this the researchers used a laser trap to put the bacteria on a surface, one at a time, thereby building up randomly, user-defined, and reproducible bacterial structures. A laser trap uses light focused through a high-magnification microscope objective to hold micron-sized objects with an index of refraction higher than that of the surrounding medium. They used Pseudomonas aeruginosa, an opportunistic bacteria that infects humans, which forms biofilms in the lungs of patients with cystic fibrosis.
They observed that small group of Pseudomonas with a size less than 10 cells developed around 15% more rapidly than when isolated in the same medium. In addition, they used Staphylococcus aureus (S. aureus), which usually appears as a co-pathogen with Pseudomonas and causes interspecies antagonism that augments the virulence of Pseudomonas infections. Importantly, the authors found that small clusters of approximately 10 Pseudomonas cells reduce the growth of S. aureus by approximately 10%. This observation contributes to a better understanding of the required conditions for the activation of Pseudomonas–S. aureus antagonism that will help to counteract harmful outcomes due to these co-infections.
The authors stated that laser trapping and the equipment used for this procedure is standard, not expensive, and should be broadly used by microbiological and physical researchers. In addition, the research team aims to apply this method to evaluate the conditions required for the P. aeruginosa virulence activation by S. aureus in terms of spatial density and distribution of both species, and the transport conditions in the environment.