Accelerated detection of extended-spectrum β-lactamases in clinical isolates of Enterobacteriaceae

Abstract

A prospective study is carried out to evaluate the performance of a protocol for the accelerated detection of extended-spectrum β-lactamases (ESBLs) in clinical isolates of Escherichia coli, Klebsiella pneumoniae and other Gram-negative bacteria. A modified double-disc test (MDDT) is incorporated in a Gram-negative template for routine susceptibility testing. The MDDT identified accurately ESBLs in all isolates subsequently confirmed as ESBLproducers by the standard Clinical Laboratory Standards Institute (CLSI) combined disc method. Of 1213 isolates tested, 98 (8%) were positive for ESBLs by MDDT and 95 (7.8%) were positive by the CLSI method. ESBLs were detected in 48 (7.8%) E. coli, 21 (8%) K. pneumoniae, 12 (5.8%) Proteus mirabilis, 13 (18.8%) Providencia stuartii and four (6.8%) Enterobacter cloacae isolates. Time required for ESBL detection by the MDDT method was one day. The protocol described provides a simple, rapid and low-cost method for early detection of ESBLs in Gram-negative bacteria.