Prevalence and molecular characterization of AmpC-producing clinical isolates of Escherichia coli from southeastern Iran.

BACKGROUND AND OBJECTIVE

AmpC in Escherichia coli is noninducible but is regulated by promoter and attenuator mechanisms and can be expressed at high levels as a result of a mutation. This study was undertaken to characterize the AmpC hyperproducing clinical isolates of E. coli.

METHODS

E. coli isolates recovered from three major hospitals in Zahedan, South Eastern Iran, were selected on the basis of resistance phenotype to the third-generation cephalosporins and cefoxitin. Phenyl boronic acid as an inhibitor and cefoxitin were used to confirm the overexpression of AmpC. The presence of genes encoding ACC, FOX, MOX, DHA, CIT, and EBC was detected using multiplex PCR. The existence of mutations in the regulatory region of the chromosomal ampC gene was assessed using PCR and sequencing.

RESULTS

Thirteen of 392 E. coli isolates were selected as high-level AmpC producers. Eleven of the 13 isolates contained the blaCMY-2 gene; 12 of the 13 AmpC hyperproducing strains harbored changes in the promoter/attenuator region, which could explain the increased expression of the chromosome-encoded AmpC enzyme. In 10 of the 13 strains, we found both chromosomal- and plasmid-mediated mechanisms responsible for AmpC production.

INTERPRETATION AND CONCLUSIONS

AmpC hyperproducing E. coli isolates exhibit significant resistance to cephalosporins. This work showed that strains hyperproducing chromosomal AmpC could be as frequent as strains with plasmid-mediated AmpC hyperproduction.