Diversification of Escherichia coli expressing an SHV-type extended- spectrum β-lactamase (ESBL) during a hospital outbreak: Emergence of an ESBL-hyperproducing strain resistant to expanded-spectrum cephalosporins

Abstract

Twelve SHV-type extended-spectrum β-lactamase (ESBL)-producing Escherichia coli lac mutant isolates were recovered in October 1997 from 11 patients of the neonatal ward in a Warsaw hospital. The outbreak was clonal; however, some of the isolates expressed a much higher level of resistance to several β-lactam antibiotics, including expanded-spectrum cephalosporins. This phenotype has been attributed to β-lactamase hyperproduction correlating with the multiplication of ESBL gene copies, as was demonstrated for representative isolates.