PARTIAL DNA-SEQUENCE OF A BETA-LACTAMASE PRODUCED BY A SHIGELLA-FLEXNERI STRAIN

A probe was constructed by radioactive labelling, and enzymatically a DNA fragment of plasmid pMAM-1, which codes for a beta-lactamase in Sh igella flexneri UCSM 129, was obtained by amplification of a small par t of the gene using the polymerase chain reaction technique (PCR). Sin ce previous published work indicated that this beta-lactamase was of t he TEM type, the primers used to amplify the gene were two highly cons erved DNA regions in all TEM beta-lactamases. A 500 bp DNA probe was o btained which, by hybridization assays, facilitated the identification of restriction fragments of the plasmid containing the beta-lactamase gene. Two DNA fragments were sequenced by the Sanger method adapted t o the PCR technique, and the sequence obtained showed a 100% homology with beta-lactamases TEM-1, TEM-2, TEM-13 and TEM-19. An intragenic re striction site, detected for Pst I, suggested that there is only one c opy of the beta-lactamase gene per plasmid copy.