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Journal of Clinical Microbiology, April 2008, p. 1317-1321, Vol. 46, No. 4
0095-1137/08/$08.00+0     doi:10.1128/JCM.00073-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Prevalence of Plasmid-Mediated AmpC β-Lactamases in a Chinese University Hospital from 2003 to 2005: First Report of CMY-2-Type AmpC β-Lactamase Resistance in China

Department of Clinical Laboratory Medicine, Sixth Affiliate Hospital of Shanghai Jiao Tong University,¹ Center of Laboratory Medicine of Huashan Hospital, Shanghai Medical College, Fudan University, Shanghai, People's Republic of China²

Received 10 January 2007/ Returned for modification 5 June 2007/ Accepted 8 January 2008

The aim of this study was to investigate the prevalences of plasmid-mediated AmpC β-lactamases (PABLs) in isolates of Escherichia coli and Klebsiella spp. from a university hospital in China. A total of 1,935 consecutive nonrepeat clinical isolates of Escherichia coli, Klebsiella pneumoniae, and Klebsiella oxytoca were collected between January 2003 and July 2005. The isolates with cefoxitin zone diameters less than 18 mm (screen positive) were selected for PCR of the bla_AmpC genes and sequencing. Fifty-four (2.79%) isolates harbored PABLs, as demonstrated by PCR and isoelectric focusing. Sequence analysis revealed the presence of bla_DHA-1 and bla_CMY-2 genes. The Southern blot hybridization studies confirmed that bla_CMY-2 and bla_DHA-1 were located on plasmids. Based on species, PABLs were detected in 4.29% (29 isolates of DHA-1 and 1 isolate of CMY-2) of K. pneumoniae, 1.91% (11 isolates of DHA-1 and 12 isolates of CMY-2) of E. coli, and 3.03% (1 isolate of DHA-1) of K. oxytoca isolates. In contrast to our anticipation, the occurrence rate of DHA-1-producing K. pneumonia significantly decreased (P < 0.01), from 7.54% in 2003 to 2.72% in 2004. The results of random amplified polymorphic DNA analysis indicate that the prevalences of DHA-1-producing K. pneumoniae and CMY-2-producing E. coli strains were not due to epidemic strains. In conclusion, DHA-1 was the most prevalent acquired AmpC beta-lactamase in this collection of isolates from a medical center in China, and DHA-1-producing K. pneumoniae was the most prevalent bacterium harboring a PABL. To the best of our knowledge, this is the first report of CMY-2-type AmpC β-lactamases in the Chinese mainland.

Published ahead of print on 27 February 2007.