Emergence of third-generation cephalosporin-resistant Enterobacteriacae in a Japanese critical care setting.

Abstract

Extended-spectrum beta-lactamases and AmpC beta-lactamases give resistance to Enterobacteriaceae against cephalosporins, which are important drugs in various clinical settings. Within 5 days, a total of eight strains of Citrobacter freundii and two strains of Escherichia coli, all of which were resistant to third-generation cephalosporins, were isolated from six different patients in a critical care center. We carried out epidemiological and genetic studies to confirm the situation to be an outbreak by a single strain or a beta-lactamase-producing gene. A review of patients' clinical data, pulsed-field gel electrophoresis epidemiological study against the strains, and polymerase chain reaction analysis for the detection of extended-spectrum beta-lactamase genes (TEM, SHV, CTX-M-1, CTX-M-2, and CTX-M-9) and multiplex polymerase chain reaction analysis for plasmid-mediated AmpC-beta-lactamase genes were carried out. Pulsed-field gel electrophoresis showed none of the subjects were genetically identical organisms. However, all strains possessed either extended-spectrum beta-lactamases (TEM, CTX-M-2, and CTX-M-9) or AmpC-beta-lactamases. One patient carried both extended-spectrum beta-lactamase- and AmpC- beta-lactamase-producing organisms. This study revealed that various types of easily transmittable drug resistance genes exist in the critical care setting concurrently. This case was not an outbreak of such strains, but the present situation might indicate a more serious condition than a mere outbreak of a single resistant strain. Enterobacteriaceae that possess extended-spectrum beta-lactamases or AmpC-beta-lactamases are increasingly common in many medical institutions in Japan, and constitutive monitoring of drug-resistant organisms and proper contact precautions are essential to prevent possible outbreaks.