Chronic infections with Pseudomonas aeruginosa persist because the bacteria form biofilms that are tolerant to antibiotic treatment and the host immune response. Scanning electron microscopy and confocal laser scanning microscopy were used to visualize biofilm development in vivo following intraperitoneal inoculation of mice with bacteria growing on hollow silicone tubes, as well as to examine the interaction between these bacteria and the host innate immune response. Wild-type P. aeruginosa developed biofilms within one day that trapped, and caused visible cavities in the polymorphonuclear leukocytes (PMNs). By contrast, the numbers of a P. aeruginosa rhlA-mutant that cannot produce rhamnolipid was significantly reduced on the implants by day one and was actively phagocytosed by infiltrating PMNs. In addition, we identified extracellular wire-like structures around the bacteria and PMNs, which we found to consist to of DNA and other polymers. Here we present a novel method to study the pathogen-host interaction in detail. The data presented provide the first direct, high-resolution visualization of the failure of PMNs to protect against bacterial biofilms.

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van Gennip M., Christensen L. D., Alhede M., Qvortrup K., Jensen P. Ø., Høiby N., Givskov M. and Bjarnsholt T.