Characterization of defective beta-lactamase genes in Yersinia enterocolitica.
OBJECTIVE
To study at the molecular level the heterogeneity of expression of the two chromosomal beta-lactamases, BlaA and BlaB, in Yersinia enterocolitica strains isolated from clinical samples.


METHODS
MIC determination by the agar dilution method and beta-lactamase assays was performed to determine the resistance level conferred by these enzymes. DNA cloning, PCR and direct sequencing were used to detect the presence of mutations.


RESULTS
The blaA allele from strain IP97 (blaA97) was found to carry a deletion of 51 bp which entirely abolished its beta-lactamase activity. Both the ampR gene and the promoter region of strain Y56 were shown to be functional by a gene swapping experiment. The blaB allele from strain Y56 was found to carry two point mutations, only one of them resulting in a change in the amino acid sequence of the protein. This single amino acid change created a practically inactive BlaB or AmpC cephalosporinase in Y. enterocolitica Y56.


CONCLUSIONS
The lack of activity observed in the beta-lactamases of some Y. enterocolitica isolates was due to the presence of point mutations or small deletions in the corresponding genes.
de la Prieta
María Carmen
MC
Departamento de Biología Molecular, Facultad de Medicina, Universidad de Cantabria, Santander, Spain.
Francia
María Victoria
MV
Seoane
Asunción
A
Lobo
Juan M García
JM
D000483:Alleles; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001483:Base Sequence; D002876:Chromosomes, Bacterial / Q000235:genetics; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000235:genetics; D017353:Gene Deletion; D005798:Genes, Bacterial; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D015008:Yersinia enterocolitica / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification; D018440:beta-Lactam Resistance; D001618:beta-Lactamases / Q000235:genetics* / Q000378:metabolism
D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D001618:beta-Lactamases