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JAC Advance Access originally published online on December 20, 2005
Journal of Antimicrobial Chemotherapy 2006 57(2):224-229; doi:10.1093/jac/dki442
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© The Author 2005. 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

Alterations of the penicillin-binding proteins and murM alleles of clinical Streptococcus pneumoniae isolates with high-level resistance to amoxicillin in Spain

Fabio Cafini1, Rosa del Campo2, Luis Alou1, David Sevillano1, María Isabel Morosini2, Fernando Baquero2, José Prieto1,* on behalf of the Spanish Pneumococcal Network (G03/103)

1 Departamento de Microbiología, Facultad de Medicina, Universidad Complutense de Madrid, Avda Complutense s/n, 28040 Madrid, Spain; 2 Servicio de Microbiología, Hospital Universitario Ramón y Cajal, Madrid, Spain

Received 30 September 2005; accepted 7 November 2005

* Corresponding author. Tel: +34-91-394-15-12; Fax: +34-91-394-15-11; E-mail: jprieto{at}med.ucm.es

Aims: The aim of this study was to analyse the nucleotide sequences of regions encoding the penicillin-binding domains of pbp1A, pbp2B and pbp2X genes and murM alleles from 14 selected amoxicillin-resistant Streptococcus pneumoniae isolates (MICs 8–16 mg/L) obtained in Spain.

Methods: PFGE and dideoxynucleotide chain termination sequencing were used.

Results: Analysis of PFGE profiles showed that the amoxicillin-resistant S. pneumoniae strains belonged to six different PFGE patterns including the Spain23F-1, Spain6B-2, Spain9V-3 and Spain14-5 international clones; however, 8 of the 14 strains belonged to the Spain9V-3 clone. These strains showed the typical changes in penicillin-binding proteins (PBPs) 1A and 2X and had 10 unique changes in the 590–641 region of PBP2B as described previously. Transformation experiments tried to incorporate the transpeptidase domain of PBP2B including the 590–641 region associated with amoxicillin-resistant pneumococci. Sequencing of the pbp2B genes revealed that part of the 3' region of the pbp2B sequence encoding a region of the domain (around amino acid 514–538 to the C terminus of PBP2B) did not recombine with the R6 pbp2B gene. The murM sequence analysis showed that 6, 6 and 2 amoxicillin-resistant S. pneumoniae strains had murMA, murMB5 and murMB6 alleles, respectively. However, strains with murMB5 or murMB6 alleles showed a single mutation (N537D) in the 537–581 region of PBP2B, while strains with the murMA allele had 12 unique changes.

Conclusions: Ten unique changes in the 590–641 region of PBP2B and no specific murM alleles were found in S. pneumoniae strains isolated in Spain with an amoxicillin MIC ≥8 mg/L (MICs from 6 to 12 mg/L by 1 mg/L step dilution). In addition, the presence of specific mutations in PBP2B seems to play a key role in the presence of different murM alleles in these amoxicillin-resistant pneumococcal strains.

Keywords: MurM , PBPs , S.pneumoniae , high-level amoxicillin resistance


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