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Antimicrobial Agents and Chemotherapy, October 2007, p. 3650-3658, Vol. 51, No. 10
0066-4804/07/$08.00+0     doi:10.1128/AAC.00601-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Role of the rapA Gene in Controlling Antibiotic Resistance of Escherichia coli Biofilms{triangledown} ,{dagger}

S. V. Lynch ,1,{ddagger},§ L. Dixon,1,{ddagger},¶ M. R. Benoit,1,{ddagger} E. L. Brodie,2 M. Keyhan,1 P. Hu,2 D. F. Ackerley,1,|| G. L. Andersen,2 and A. Matin1*

Department of Microbiology and Immunology, Sherman Fairchild Science Building, Stanford University School of Medicine, 299 Campus Drive, Stanford, California 94305,1 Ecology Department, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 947202

Received 8 May 2007/ Returned for modification 3 July 2007/ Accepted 25 July 2007

By using a high-throughput screening method, a mutant of a uropathogenic Escherichia coli strain affected in the rapA gene was isolated. The mutant 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 with mutations in this gene also formed biofilms with decreased resistance, although the effect was less pronounced than that of the rapA mutation. Thus, an additional mechanism(s) controlled by a rapA-regulated gene(s) was involved in wild-type biofilm resistance. The 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 quantities and coverage in the mutant biofilms. Furthermore, the (fluorescent) functional penicillin G homologue Bocillin FL penetrated the mutant biofilms more readily. The results strongly suggest a dual mechanism for the wild-type biofilm penicillin G resistance, retarded penetration, and effective efflux. The results of studies with an E. coli K-12 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 also more sensitive to norfloxacin, chloramphenicol, and gentamicin.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, Sherman Fairchild Science Building, Stanford University School of Medicine, 299 Campus Drive, Stanford, CA 94305-5124. Phone: (650) 725-4745. Fax: (650) 725-6757. E-mail: a.matin{at}stanford.edu

{triangledown} Published ahead of print on 30 July 2007.

{dagger} Supplemental material for this article may be found at http://aac.asm.org/.

{ddagger} S. V. Lynch, L. Dixon, and M. R. Benoit contributed equally to this work.

§ Present address: Department of Anesthesia and Perioperative Care, UCSF Medical School, 513 Parnassus Ave., S261, San Francisco, CA 94143.

Present address: Biosciences Division, Mailstop M888, Los Alamos National Laboratory, Los Alamos, NM 87545.

|| Present address: School of Biological Sciences, Victoria University of Wellington, Wellington, New Zealand.

Antimicrobial Agents and Chemotherapy, October 2007, p. 3650-3658, Vol. 51, No. 10
0066-4804/07/$08.00+0     doi:10.1128/AAC.00601-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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  • Zhang, L., Mah, T.-F. (2008). Involvement of a Novel Efflux System in Biofilm-Specific Resistance to Antibiotics. J. Bacteriol. 190: 4447-4452 [Abstract] [Full Text]  


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