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Antimicrob. Agents Chemother. doi:10.1128/AAC.00601-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Role of the rapA Gene in Controlling Antibiotic Resistance of Escherichia coli Biofilms

Department of Microbiology and Immunology, Sherman Fairchild Science Building, Stanford University School of Medicine, 299 Campus Drive, Stanford, CA 94305, USA; Ecology Department, Lawrence Berkeley National Lab, 1 Cyclotron Road, Berkeley, CA 94720, USA

^* To whom correspondence should be addressed. Email: a.matin{at}stanford.edu.

	Abstract

Using a high throughput screening method, a mutant in the uropathogenic E. coli strain affected in the rapA gene was isolated, which formed normal architecture biofilms, but showed decreased penicillin G resistance, although the mutation did not affect planktonic cell resistance. Transcriptome analysis showed that 22 genes were down-regulated in the mutant biofilm. One of these genes was yhcQ, which encodes a putative multidrug resistance pump. Mutants in this gene also formed biofilms with decreased resistance, although the effect was less pronounced than that of rapA mutation. Thus, an additional mechanism(s) controlled by a rapA-regulated gene(s) was involved in the wild type biofilm resistance. Search for this mechanism was guided by the fact that another down-regulated gene in rapA biofilms, yeeZ, is suspected to be involved in extra cell wall related functions. A comparison of the biofilm matrix of the wild type and rapA strains revealed decreased polysaccharide quantity and coverage in the mutant biofilms. Furthermore, the (fluorescent) functional penicillin G homologue, Bocillin^TM FL penetrated more readily in the mutant biofilms. The results strongly suggest a dual mechanism for the wild type biofilm penicillin G resistance, retarded penetration and effective efflux. Studies with an E. coli K12 strain pointed to the same conclusion. Since efflux and penetration can be general resistance mechanisms, tests were conducted with other antibiotics. The rapA biofilm was more sensitive also to norfloxacin, chloramphenicol, and gentamycin.

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