Biofilm-Forming by Carbapenem Resistant Enterobacteriaceae May Contribute to the Blood Stream Infection

Abstract

Bloodstream infection (BSI) due to carbapenem-resistant Enterobacteriaceae (CRE) has a high mortality rate and is a serious threat worldwide. Ten CRE strains (eight <i>Enterobacter cloacae</i>, one <i>Klebsiella pneumoniae</i> and one <i>Citrobacter freundii</i>) were isolated from the blood of nine patients, a percentage of whom had been treated with indwelling devices. The steps taken to establish cause included minimum inhibitory concentration (MIC) tests, a pulsed-field gel electrophoresis (PFGE), biofilm study, a multiplex PCR for resistant genes of carbapenemases and extended-spectrum beta-lactamases (ESBLs), and plasmid incompatibility typing. All strains showed a tendency toward resistance to multiple antibiotics, including carbapenems. Frequently isolated genes of ESBLs and carbapenemases include <i>bla</i>_TEM-1 (four strains), <i>bla</i>_SHV-12 (four strains) and <i>bla</i>_IMP-1 (six strains). A molecular analysis by PFGE was used to divide the <i>Xba</i>I-digested genomic DNAs of 10 CRE strains into eight patterns, and the analysis showed that three <i>E. cloacae</i> strains detected from two patients were either identical or closely related. The biofilm production of all CRE strains was examined using a microtiter biofilm assay, and biofilm growth in continuous flow chambers was observed via the use of a confocal laser scanning microscope. Our study indicates that biofilm formation on indwelling devices may pose a risk of BSI due to CRE.