Bacterial Biofilms and Infection
It has been widely reported in the literature that the formation of bacterial biofilms is a major contributory factor in the development of severe hospital acquired infections, particularly those affecting the urinary tract. Of increasing concern is the knowledge that biofilm formation during infection can reduce the efficacy of current treatment options by providing antibiotic protection to the immediate bacterial community. Recently, Floyd and colleagues have investigated the spatial proteome of surface-associated biofilms produced by uropathogenic Escherichia coli (UPEC). UPEC are the most common infectious agent implicated in community-acquired urinary tract infections causing 70- to 90% of the annual 7 million and 250,000 cases of acute cystitis and pyelonephritis, respectively, in the United States.
Using matrix-assisted laser desorption/ionization time of flight imaging mass spectrometry (MALDI TOF IMS), Floyd and colleagues were able to demonstrate the differential localization of two virulence-associated adhesive fibers (type I pili and curli amyloid fibers) within the UPEC biofilm structure. More specifically, type I pili were found exclusively at the air exposed region of the biofilm whilst the curli amyloid fibers localized to the air-liquid interface of the structure. The authors were also able to demonstrate that the type I pilus promoter was switched off under conditions of oxygen depletion, with concurrent up-regulation of S pilus expression. Interestingly, for anaerobically grown cells, genetic tethering of the type I pilus promoter in the on position only restored pilus production in the presence of an alternative terminal electron acceptor.
Taken together these findings indicate the presence of at least two regulatory mechanisms controlling type I pilusgene expression in response to oxygen availability. Furthermore, these mechanisms may contribute to the stratification of extracellular matrix components within the biofilm. This study shows that MALDI TOF IMS can be used specifically to interrogate biofilm structure and composition at different surfaces. Strikingly, identifying the spatial proteome of biofilms may uncover markers for distinct bacterial sub-populations within the structure that could enhance antibiotic treatment in the future.
Original Research Article:
PLoS Pathog. 2015 Mar 4;11(3):e1004697. doi: 10.1371/journal.ppat.1004697. eCollection 2015.
Adhesive Fiber Stratification in Uropathogenic Escherichia coli Biofilms Unveils Oxygen-Mediated Control of Type 1 Pili.
Image: “EscherichiaColi NIAID” by Credit: Rocky Mountain Laboratories, NIAID, NIH – NIAID: http://commons.wikimedia.org/wiki/File:EscherichiaColi_NIAID.jpg
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