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Antimicrobial Agents and Chemotherapy, March 2008, p. 822-830, Vol. 52, No. 3
0066-4804/08/$08.00+0     doi:10.1128/AAC.00731-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Fitness of Streptococcus pneumoniae Fluoroquinolone-Resistant Strains with Topoisomerase IV Recombinant Genes{triangledown}

Luz Balsalobre and Adela G. de la Campa*

Unidad de Genética Bacteriana, Centro Nacional de Microbiología and Ciber Enfermedades Respiratorias, Instituto de Salud Carlos III, 28220 Majadahonda, Madrid, Spain

Received 6 June 2007/ Returned for modification 20 August 2007/ Accepted 19 December 2007

The low prevalence of ciprofloxacin-resistant (Cpr) Streptococcus pneumoniae isolates carrying recombinant topoisomerase IV genes could be attributed to a fitness cost imposed by the horizontal transfer, which often implies the acquisition of larger-than-normal parE-parC intergenic regions. A study of the transcription of these genes and of the fitness cost for 24 isogenic Cpr strains was performed. Six first-level transformants were obtained either with PCR products containing the parC quinolone resistance-determining regions (QRDRs) of S. pneumoniae Cpr mutants with point mutations or with a PCR product that includes parE-QRDR-ant-parC-QRDR from a Cpr Streptococcus mitis isolate. The latter yielded two strains, T6 and T11, carrying parC-QRDR and parE-QRDR-ant-parC-QRDR, respectively. These first-level transformants were used as recipients in further transformations with the gyrA-QRDR PCR products to obtain 18 second-level transformants. In addition, strain Tr7 (which contains the GyrA E85K change) was used. Reverse transcription-PCR experiments showed that parE and parC were cotranscribed in R6, T6, and T11; and a single promoter located upstream of parE was identified in R6 by primer extension. The fitness of the transformants was estimated by pairwise competition with R6 in both one-cycle and two-cycle experiments. In the one-cycle experiments, most strains carrying the GyrA E85K change showed a fitness cost; the exception was recombinant T14. In the two-cycle experiments, a fitness cost was observed in most first-level transformants carrying the ParC changes S79F, S79Y, and D83Y and the GyrA E85K change; the exceptions were recombinants T6 and T11. The results suggest that there is no impediment due to a fitness cost for the spread of recombinant Cpr S. pneumoniae isolates, since some recombinants (T6, T11, and T14) exhibited an ability to compensate for the cost.

* Corresponding author. Mailing address: Unidad de Genética Bacteriana, Centro Nacional de Microbiología and Ciber Enfermedades Respiratorias, Instituto de Salud Carlos III, 28220 Majadahonda, Madrid, Spain. Phone: (34) 91 509 7057. Fax: (34) 91 509 7919. E-mail: agcampa{at}isciii.es

{triangledown} Published ahead of print on 26 December 2007.

Antimicrobial Agents and Chemotherapy, March 2008, p. 822-830, Vol. 52, No. 3
0066-4804/08/$08.00+0     doi:10.1128/AAC.00731-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Martinez, J. L. (2009). The role of natural environments in the evolution of resistance traits in pathogenic bacteria. Proc R Soc B 276: 2521-2530 [Abstract] [Full Text]  


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