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Antimicrobial Agents and Chemotherapy, November 2009, p. 4628-4639, Vol. 53, No. 11
0066-4804/09/$08.00+0     doi:10.1128/AAC.00454-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Induction of Multidrug Resistance Mechanism in Escherichia coli Biofilms by Interplay between Tetracycline and Ampicillin Resistance Genes{triangledown} ,{dagger}

Thithiwat May, Akinobu Ito, and Satoshi Okabe*

Graduate School of Engineering, Hokkaido University, Kita-13, Nishi-8, Kita-Ku, Sapporo 060-8628, Japan

Received 6 April 2009/ Returned for modification 10 June 2009/ Accepted 21 August 2009

Biofilms gain resistance to various antimicrobial agents, and the presence of antibiotic resistance genes is thought to contribute to a biofilm-mediated antibiotic resistance. Here we showed the interplay between the tetracycline resistance efflux pump TetA(C) and the ampicillin resistance gene (blaTEM-1) in biofilms of Escherichia coli harboring pBR322 in the presence of the mixture of ampicillin and tetracycline. E. coli in the biofilms could obtain the high-level resistance to ampicillin, tetracycline, penicillin, erythromycin, and chloramphenicol during biofilm development and maturation as a result of the interplay between the marker genes on the plasmids, the increase of plasmid copy number, and consequently the induction of the efflux systems on the bacterial chromosome, especially the EmrY/K and EvgA/S pumps. In addition, we characterized the overexpression of the TetA(C) pump that contributed to osmotic stress response and was involved in the induction of capsular colanic acid production, promoting formation of mature biofilms. However, this investigated phenomenon was highly dependent on the addition of the subinhibitory concentrations of antibiotic mixture, and the biofilm resistance behavior was limited to aminoglycoside antibiotics. Thus, marker genes on plasmids played an important role in both resistance of biofilm cells to antibiotics and in formation of mature biofilms, as they could trigger specific chromosomal resistance mechanisms to confer a high-level resistance during biofilm formation.

* Corresponding author. Mailing address: Graduate School of Engineering, Hokkaido University, Kita-13, Nishi-8, Kita-Ku, Sapporo 060-8628, Japan. Phone and fax: 81-11-706-6266. E-mail: sokabe{at}eng.hokudai.ac.jp

{triangledown} Published ahead of print on 31 August 2009.

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

Antimicrobial Agents and Chemotherapy, November 2009, p. 4628-4639, Vol. 53, No. 11
0066-4804/09/$08.00+0     doi:10.1128/AAC.00454-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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