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Journal of Clinical Microbiology, March 2006, p. 909-915, Vol. 44, No. 3
0095-1137/06/$08.00+0 doi:10.1128/JCM.44.3.909-915.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Ingo Sobottka,1
Matthias A. Horstkotte,1
Stefanie Scherpe,1
Martin Aepfelbacher,1 and
Susanne Müller2
Institut für Infektionsmedizin, Universitätsklinikum Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany,1 SEQUENOM GmbH, Mendelssohnstrasse 15D, 22761 Hamburg, Germany2
Received 11 August 2005/ Returned for modification 3 October 2005/ Accepted 6 January 2006
Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) after base-specific cleavage of PCR-amplified and in vitro-transcribed blaSHV genes was used for the identification and genotyping of SHV ß-lactamases. For evaluation, blaSHV stretches of 21 clinical Enterobacteriaceae isolates were PCR amplified using T7 promoter-tagged forward and reverse primers, respectively. In vitro transcripts were generated with T7 RNA and DNA polymerase in the presence of modified analogues replacing either CTP or UTP. Using RNase A, the in vitro transcripts were base-specifically cleaved at every "T" or "C" position. Resulting cleavage products were analyzed by MALDI-TOF MS, generating a characteristic signal pattern based on the fragment masses. All 21 individual SHV genes were identified unambiguously using reference sequences, and the results were in perfect concordance with those obtained by fluorescent dideoxy sequencing, which represents the current standard method. As multiple point mutations can be detected in a single assay and newly emerged mutations which are not yet described in public databases can be identified too, MALDI-TOF MS appears to be an ideal tool for analysis of sequence polymorphisms in resistance-associated gene loci.
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