Detection of serinocarbapenemases Class A and other mechanisms of enzymatic resistance to β-lactams in enterobacteria strains with diminished susceptibility to carbapenems isolated of patients in a university hospital

Abstract

The emergence of carbapenemase mediated resistance in Enterobacteriaceae has a strong clinical impact. This study aimed to do a genotypic and phenotypic characterization of the enzymatic resistance to β-lactams in clinical Enterobacteriaceae isolates with decreased susceptibility to carbapenems in a university medical center in Santiago. During April-September 2010 at Hospital Clinico Universidad de Chile, 23 isolates of carbapenem non susceptible Enterobacteriaceae were collected. We used PCR for the detection of class A carbapenemases (SME, IMI, NMC, GES and KPC) and the modified Hodge with the boronic acid test to phenotypically assess the presence of serine-carbapenemases. To assess extended spectrum β-lactamases (ESBLs) the CLSI phenotypic tests were performed. Metallo-β-lactamases (MBL) and AmpC were assessed with commercial tablets. 18/23 were Klebsiellapneumoniae and 5/23 strains were Enterobacter cloacae. All PCR to class A carbapenemases were negative. 3/23 strains (all E. cloacae), were positive to the Hodge modified test and 1/23, a K.pneumoniae, was positive to the boronic acid test. ESBLs were detected in 14/23 os the strains and AmpC in 5/23. No MBL was detected. No class A serine-carbapenemasa was detected. The decreased susceptibility to carbapenems is probably explained by the β-lactamase activity and due to porin loss.