Molecular Characterization of ESBL and AmpC β-Lactamases among Blood Isolates of Klebsiella pneumoniae and Escherichia coli

Abstract

The purpose of this study was to determine the mechanisms of third generation cephalosporins resistance among blood isolates of Klebsiella pneumoniae and Escherichia coli. A total of 549 isolates, Klebsiella pneumoniae (n=369) and Escherichia coli (n=180) were included. Antibiotic susceptibility pattern, phenotypic and genotypic detection of ESBL and AmpC production were carried out. The genetic environment surrounding blaCTX-M gene was assessed for insertion sequences. The plasmid-mediated quinolone resistance (PMQR) and integron carriage rate of ESBL producers were studied. The clonality was assessed by pulsed-field gel electrophoresis.  Also, the plasmids bearing the ESBL, AmpC genes were studied by incompatibility typing and conjugation assay. By phenotypic tests, K. pneumoniae (79.8%) and E. coli (74.1%) were ESBL producers. Similarly, K. pneumoniae (70.5%) and E. coli (76.8%) were AmpC producers. By PCR, K. pneumoniae (68%) and E. coli (62%) carried ESBL genes. blaCTX-M- 15 was the prevalent type (98.1%). The linkage of ISEcp1 with blaCTX-M-15 gene was found in 92.5% of the blaCTX-M-15 genes. blaCMY-2 was present in 57% isolates. PFGE showed no clonal relatedness however; replicon typing revealed that ESBL genes were carried on 5 different replicon types, IncA/C being the commonest type present in this region. Also, PMQR was found in 19.3% of the ESBL producers. As high as 21.5% of class 2 integron was noted for first time from this region. A high prevalence of ESBL and AmpC genes was noticed. The clonal diversity, transferability of blaCTX-M plasmids suggest a higher incidence and wider distribution of ESBL and AmpC producing bacteria existing in the South India.