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JAC Advance Access originally published online on October 16, 2009
Journal of Antimicrobial Chemotherapy 2009 64(6):1165-1169; doi:10.1093/jac/dkp364
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© The Author 2009. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Original research

High clonal diversity in erythromycin-resistant Streptococcus pneumoniae invasive isolates in Madrid, Spain (2000–07)

Elia Gómez G. de la Pedrosa1,2, Fernando Baquero1,2, Elena Loza1, José-María Nadal-Serrano1, Asunción Fenoll3, Rosa del Campo1,2 and Rafael Cantón1,2,*

1 Servicio de Microbiología, Hospital Ramón y Cajal y CIBER en Epidemiología y Salud Pública (CIBERESP), Madrid, Spain 2 Unidad de Resistencia a Antibióticos y Virulencia Bacteriana asociada al Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain 3 Spanish Reference Laboratory for Pneumococci, Instituto de Salud Carlos III, Madrid, Spain

Received 23 May 2009; returned 24 June 2009; revised 12 September 2009; accepted 18 September 2009

* Corresponding author. Servicio de Microbiología, Hospital Ramón y Cajal, Madrid, Spain. Tel: +34-913368832; Fax: +34-913368809; E-mail: rcanton.hrc{at}salud.madrid.org

Objectives: Erythromycin resistance in Streptococcus pneumoniae is still increasing worldwide. All 78 erythromycin-resistant S. pneumoniae isolates collected from blood cultures in our hospital (2000–07) were studied and the population structure was analysed by using different mathematical diversity indexes.

Methods: Erythromycin resistance determinants were screened by PCR. The population structure, including multilocus sequence typing, was analysed by using quantitative clonal diversity (diversity ratio, Simpson, Selander–Levin and Shannon mathematical indexes).

Results: The leading resistance gene was erm(B) (74.3% of the isolates), followed by the erm(B) plus mef(A) combination (17.9%) and mef(A) alone (7.7%). The most frequent serotypes were 14 (18%), 19A (15.4%) and 6B (11.5%). A polyclonal structure was detected in resistant strains, including the Spain9V-3, Spain6B-2 and Denmark14-32 international clones. Both genetic diversity and genetic distribution were high, particularly among clones containing erm(B) and erm(B) plus mef(A) determinants.

Conclusions: The resistance determinants erm(B) and the combination of erm(B) plus mef(A) were observed within multiple S. pneumoniae bacteraemic clones. The preservation of a polyclonal structure might provide a suitable background for further evolution of antibiotic resistance.

Keywords: pneumococcal blood isolates , macrolide resistance , clonal diversity indexes


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