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A genetic basis for Pseudomonas aeruginosa biofilm antibiotic resistance


Biofilms are surface-attached microbial communities with characteristic architecture and phenotypic and biochemical properties distinct from their free-swimming, planktonic counterparts1. One of the best-known of these biofilm-specific properties is the development of antibiotic resistance that can be up to 1,000-fold greater than planktonic cells2. We report a genetic determinant of this high-level resistance in the Gram-negative opportunistic pathogen, Pseudomonas aeruginosa. We have identified a mutant of P. aeruginosa that, while still capable of forming biofilms with the characteristic P. aeruginosa architecture, does not develop high-level biofilm-specific resistance to three different classes of antibiotics. The locus identified in our screen, ndvB, is required for the synthesis of periplasmic glucans. Our discovery that these periplasmic glucans interact physically with tobramycin suggests that these glucose polymers may prevent antibiotics from reaching their sites of action by sequestering these antimicrobial agents in the periplasm. Our results indicate that biofilms themselves are not simply a diffusion barrier to these antibiotics, but rather that bacteria within these microbial communities employ distinct mechanisms to resist the action of antimicrobial agents.

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We thank L.-X. Wang for discussions. This work was supported by grants from the NSF to P.S.S., from the NIH to G.C.W, from the Canadian Cystic Fibrosis Foundation to T.-F.M. and from the NIH, Microbia, Inc. and The Pew Charitable Trusts to G.A.O'T., who is a Pew Scholar in the Biomedical Sciences.

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Correspondence to George A. O'Toole.

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G.A.O'T. has stock options for and consults with Microbia, Inc., which provided some funding for this study.

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Figure 1: Flow cell assay for antibiotic sensitivity.
Figure 2: Colony biofilm assay for antibiotic sensitivity.
Figure 3: Periplasmic glucans interact with Tb.
Figure 4: ndvB is preferentially expressed in biofilms.


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