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Journal of Clinical Microbiology, May 2007, p. 1478-1482, Vol. 45, No. 5
0095-1137/07/$08.00+0 doi:10.1128/JCM.02470-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Women's and Children's Hospital, Adelaide, South Australia, Australia,1 School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, South Australia, Australia,2 School of Medicine, Shahed University, Tehran, Iran,3 JMI Laboratories, North Liberty, Iowa4
Received 10 December 2006/ Returned for modification 12 February 2007/ Accepted 23 February 2007
A negative extended-spectrum ß-lactamase (ESBL) confirmation test result obtained after a positive ESBL screening test result using Clinical and Laboratory Standards Institute methods has been a common occurrence among isolates of Escherichia coli and Klebsiella pneumoniae in the SENTRY Antimicrobial Surveillance Program in the Asia-Pacific region. Among isolates collected between 1998 and 2004 this screen-positive, nonconfirmed profile (failed to show clavulanate synergy) was observed in 8.9% of 4,515 E. coli isolates and 20.3% of 2,303 K. pneumoniae isolates. We then selected 52 E. coli isolates and 68 K. pneumoniae isolates with a negative ESBL confirmation test, as well as comparable number of isolates with confirmed ESBL-positive tests, and examined them for the presence of TEM, SHV, plasmid-borne ampC, and CTX-M genes. We found that 62% of nonconfirming E. coli isolates and 75% of nonconfirming K. pneumoniae harbored a plasmid-borne AmpC enzyme of the CIT or DHA type. The majority of nonconfirming E. coli and K. pneumoniae from the Asia-Pacific region harbor important ß-lactamases, and a positive screening test alone should be sufficient grounds to report resistance to extended-spectrum cephalosporins in this region.
Published ahead of print on 7 March 2007.
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