Response of regulatory, efflux pump transporter and Omp genes during prolonged antibiotic stress and development of MDR in Gram-negative bacteria

Abstract number: S388

Amaral L., Viveiros M., Rodrigues L., Martins M., Spengler G., Martins A., Pages J-M., Fanning S.

Multi-drug resistance of Gram-negative bacteria is now known to be the result of over-expressed efflux pumps that extrude a variety of unrelated antibiotics prior to their reaching their targets. Although a number of methods have been developed for the assessment of over-expressed efflux such as the use of the universal efflux pump substrate ethidium bromide (EB) or the use of radiolabeled antibiotics in the presence and absence of an inhibitor of efflux pumps, these methods are labour intensive, are relatively imprecise and do not lend themselves for inter-laboratory use. We have developed a number of methods that A) identify over-expressed efflux activity of mdr pathogenic bacteria without the use of specialised instrumentation (1); B) assess specific activity of genes that regulate or code for transporter component of RND efflux pumps (2); C) assess and evaluate over-all efflux pump activity via a semi-automated system that distinguishes accumulation of EB from its efflux, can also identify agents that inhibit efflux activity as well as define conditions that control accumulation and efflux (3). Method C will be fully described for the assessment and evaluation of intrinsic and over-expressed efflux activity of mdr E. coli, Enterobacter aerogenes and Salmonella.


1. Martins M, Santos B, Couto I, Viveiros M, Pages JM, Molnar M, Cruz A and Amaral L. Instrument free method for the demonstration and assessment of efflux pumps that cause bacterial resistance. In Vivo 2006; 20:657–664.

2. Viveiros M, Rodrigues l, Dupont M, Martins M, Couto I, Pagès JM, and Amaral L. Antibiotic Stress, Genetic Response and Altered Permeability of E. coli PLOS ONE 2007; 2:e365.doi:10.1371/journal.pone.0000365.

3. Viveiros M, Martins A, Paxão L, Rodrigues L, Kern W, Couto I and Amaral L. Demonstration of intrinsic efflux activity of Gram-negative bacteria by an automated ethidium bromide method. International Journal of Antimicrobial Agents 2008; In Press.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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