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Antimicrobial Agents and Chemotherapy, July 2007, p. 2574-2581, Vol. 51, No. 7
0066-4804/07/$08.00+0     doi:10.1128/AAC.00174-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Influence of High Mutation Rates on the Mechanisms and Dynamics of In Vitro and In Vivo Resistance Development to Single or Combined Antipseudomonal Agents{triangledown}

V. Plasencia, N. Borrell, M. D. Maciá, B. Moya, J. L. Pérez, and A. Oliver*

Servicio de Microbiología and Unidad de Investigación, Hospital Son Dureta, Instituto Universitario de Investigación en Ciencias de la Salud (IUNICS), Palma de Mallorca, Spain

Received 6 February 2007/ Returned for modification 17 April 2007/ Accepted 24 April 2007

We studied the mechanisms and dynamics of the development of resistance to ceftazidime (CAZ) alone or combined with tobramycin (TOB) or ciprofloxacin (CIP) in vitro and in vivo (using a mouse model of lung infection with human antibiotic regimens). Pseudomonas aeruginosa strain PAO1 and its hypermutable derivative PAO{Delta}mutS were used, and the results were compared with those previously obtained with CIP, TOB, and CIP plus TOB (CIP-TOB) under the same conditions. An important (200-fold) amplification of the number of resistant mutant cells was documented for PAO{Delta}mutS-infected mice that were under CAZ treatment compared to the number for mice that received placebo, whereas the median number of resistant mutant cells was below the detection limits for mice infected by PAO1. These results were intermediate between the high amplification with CIP (50,000-fold) and the low amplification with TOB (10-fold). All CAZ-resistant single mutant cells selected in vitro or in vivo hyperproduced AmpC. On the other hand, the three combinations studied were found to be highly effective in the prevention of in vivo resistance development in mice infected with PAO{Delta}mutS, although the highest therapeutic efficacy (in terms of mortality and total bacterial load reduction) compared to those of the individual regimens was obtained with CIP-TOB and the lowest was with CAZ-CIP. Nevertheless, mutant cells that were resistant to the three combinations tested were readily selected in vitro for PAO{Delta}mutS (mutation rates from 1.2 x 10–9 to 5.8 x 10–11) but not for PAO1, highlighting the potential risk for antimicrobial resistance development associated with the presence of hypermutable strains, even when combined therapy was used. All five independent CAZ-TOB-resistant PAO{Delta}mutS double mutants studied presented the same resistance mechanism (AmpC hyperproduction plus an aminoglycoside resistance mechanism not related to MexXY), whereas four different combinations of resistance mechanisms were documented for the five CAZ-CIP-resistant double mutants.

* Corresponding author. Mailing address: Servicio de Microbiología, Hospital Son Dureta, C. Andrea Doria no. 55, 07014 Palma de Mallorca, Spain. Phone: 34 971 175 185. Fax: 34 971 175 185. E-mail: aoliver{at}hsd.es

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

Antimicrobial Agents and Chemotherapy, July 2007, p. 2574-2581, Vol. 51, No. 7
0066-4804/07/$08.00+0     doi:10.1128/AAC.00174-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Mandsberg, L. F., Ciofu, O., Kirkby, N., Christiansen, L. E., Poulsen, H. E., Hoiby, N. (2009). Antibiotic Resistance in Pseudomonas aeruginosa Strains with Increased Mutation Frequency Due to Inactivation of the DNA Oxidative Repair System. Antimicrob. Agents Chemother. 53: 2483-2491 [Abstract] [Full Text]  
  • Mulet, X., Macia, M. D., Mena, A., Juan, C., Perez, J. L., Oliver, A. (2009). Azithromycin in Pseudomonas aeruginosa Biofilms: Bactericidal Activity and Selection of nfxB Mutants. Antimicrob. Agents Chemother. 53: 1552-1560 [Abstract] [Full Text]  
  • Macia, M. D., Mena, A., Borrell, N., Perez, J. L., Oliver, A. (2007). Increased Susceptibility to Colistin in Hypermutable Pseudomonas aeruginosa Strains from Chronic Respiratory Infections. Antimicrob. Agents Chemother. 51: 4531-4532 [Full Text]  


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