[A new member of CMY type cephalosporinase prevailing in Escherichia coli].

OBJECTIVE

To study the resistant phenotype and molecular biology character of plasmid mediated high AmpC-producing clinical isolates of Escherichia coli and to find new AmpC genotype.

METHODS

The cefoxitin highly resistant clinical isolates of Escherichia coli were studied by K-B method, three-dimensional method, Isoelectric Focusing (IEF) and the MIC of these strains were examined by micro-dilution method. The conjugation experiment, multiplex PCR and DNA sequencing methods were used in further study.

RESULTS

Above 719 strains studied, there are 6 isolates were showed as high AmpC-producing by three-dimensional method and IEF found they could produce a beta-Lactamase which PI was 8.9 and could be inhibited by cloxacillin but not by clavulnate. The strains were resistant to most of third generation cephalosporins, but were susceptible to cefepime, meropenem and imipenem. The experiment also showed that the gene which express this AmpC like beta-Lactamase could be transferable. Multiplex PCR indicated they belong to Citrobacter freundii family. Sequencing of corresponding DNA revealed 99% identities of the deduced amino acid sequence with CMY-2 and CMY-7 respectively. It is a new CMY type cephalosporinase.

CONCLUSION

A new CMY type cephalosporinase has been found in clinical strains of Escherichia coli in our hospital. It was resistant to many antibiotics and its resistance could be transferred horizontally.