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JAC Advance Access published online on December 20, 2005
Journal of Antimicrobial Chemotherapy, 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
Received September 30, 2005
Accepted November 7, 2005

Original article

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

Fabio Cafini 1, Rosa del Campo 2, Luis Alou 1, David Sevillano 1, María Isabel Morosini 2, Fernando Baquero 2, José Prieto 1 *, and 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

* To whom correspondence should be addressed.
José Prieto, E-mail: jprieto{at}med.ucm.es


  Abstract

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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