OBJECTIVE

To investigate the expression of AmpC beta-lactamases and ESBL among clinical isolates of E. cloacae and its impact on antibiotic susceptibility.

METHODS

Antibiotic susceptibility was determined by standard agar dilution procedures. beta-lactamases of the isolates with decreased susceptibilities to ceftazidime, cefotaxime, ceftriaxon or aztreonam were investigated by three-dimensional extract tests, isoelectric focusing overlay technique, conjugation experiments and PCR.

RESULTS

Among 106 E. cloacae isolates, 16.0% produced only high-level AmpC beta-lactamases, 10.4% produced only ESBL, 13.2% produced both high-level AmpC beta-lactamases and ESBL. 18 isolates (17.0%) carried CTX-M-type ESBL and 7 isolates (6.6%) carried SHV-type ESBL. All carbapenems showed high activity against E. cloacae strains (MIC90 <or= 2 micro g/ml). More than 70% of the isolates producing only high-level AmpC beta-lactamases were susceptible to cefepime, amikacin, gentamicin or ciprofloxacin. More than 60% of the isolates producing only ESBL were susceptible to piperacillin/tazobactam, cefoperazone/sulbactam, ciprofloxacin or amikacin. The susceptible rates of the isolates producing both high-level AmpC beta-lactamases and ESBL to tested antimicrobial agents other than carbapenems were all lower than 25%.

CONCLUSION

CTX-M-type ESBL was prevalent among clinical isolates of E. cloacae. Resistance to expanded-spectrum cephalosporins in E. cloacae was mediated not only by AmpC beta-lactamases but also by ESBL. Expression of ESBL in high-level AmpC beta-lactamases producing strains resulted in a significant rise in resistance level.