LAUSR

Background The bloodstream infections (BSI) caused by Escherichia coli pose a serious threat to human health. To explore molecular characteristics of E. coli causing BSI, we collected E. coli isolates causing BSI in Huashan Hospital, Shanghai, China during 2010–2015. Methods In all E. coli isolates causing BSI collected from this study, polymerase chain reaction (PCR) was used to detect ESBLs and carbapenemase genes, and minimum inhibitory concentrations (MICs) were determined with agar dilution method. Outer membrane proteins were examined by SDS-PAGE in carbapenem-resistant strains. The genetic background of blaKPC gene was investigated by combining next-generation sequencing with a PCR mapping approach. Conjugation and transformation experiments were performed to verify the mobilization of blaKPC. The transcription levels of the blaKPC gene were measured by RT-PCR. Results During 2010–2015, a total of 207 E. coli BSI strains were isolated. The positive rates of β-lactamase resistant genes were 0.48% (blaKPC), 57% (blaTEM), 23.67% (blaCTX-M-1), 18.84% (blaCTX-M-9), and 1.93% (blaSHV). High rates of blaTEM, blaCTX-M-1, and blaCTX-M-9 were consistent with the poor activity of third-generation cephalosporins and aztreonam in vitro, except for carbapenem and β-lactamase inhibitor combinations. Low susceptibility rates were observed for piperacillin (25.1%) in contrast to the increased susceptibility when combined with β-lactamase inhibitors, namely piperacillin-tazobactam (90.8%). Only one KPC-producing E. coli strain was detected. Despite the combination of OmpC loss, the low expression level of KPC may be responsible for its lower resistance to carbapenems compared to E. coli DH5α (pKP12-100). Conclusion E. coli strains isolated from BSI were still highly susceptible to carbapenems and β-lactamase inhibitor combinations, and blaCTX-M was the dominant genotype of ESBLs. The low expression of blaKPC may be the reason for the low resistance to carbapenems.