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Abstract
This study was performed to assess the prevalence and genotypes of plasmid-borne extended-spectrum β-lactamases (ESBLs) and AmpC β-lactamases in Escherichia coli in Korea. A total of 576 isolates of E. coli was collected from 12 Korean hospitals during May and July 2007. A phenotypic confirmatory test detected ESBLs in 82 (14.2 %) of the 576 E. coli isolates. The most common types of ESBLs identified were CTX-M-14 (n=32) and CTX-M-15 (n=27). The prevalence and diversity of the CTX-M mutants, including CTX-M-15, CTX-M-27 and CTX-M-57, with significant hydrolytic activity against ceftazidime were increased. PCR experiments detected genes encoding plasmid-borne AmpC β-lactamases in 15/56 cefoxitin-intermediate or cefoxitin-resistant isolates, and the most common type of AmpC β-lactamase identified was DHA-1 (n=10). These data suggest that the incidence of ESBLs in E. coli has increased as a result of the dissemination of CTX-M enzymes in Korea. In addition, CTX-M-22, CTX-M-27 and CTX-M-57 have appeared in Korea.
Highlights
The predominant mechanism for acquired resistance to blactams in Escherichia coli is the synthesis of plasmid-borne extended-spectrum b-lactamases (ESBLs) and AmpC blactamases
Clinical isolates with an ESBL phenotype were found in all 12 hospitals (Table 2)
We have shown previously that only 3.3 % (8/246) of clinical E. coli isolates produced CTX-M ESBLs in 2003 (Ryoo et al, 2005), but the prevalence of these enzymes increased to 13.4 % (77/576) in the present study
Summary
The predominant mechanism for acquired resistance to blactams in Escherichia coli is the synthesis of plasmid-borne extended-spectrum b-lactamases (ESBLs) and AmpC blactamases. CTXM enzymes are spreading rapidly and are the dominant type of ESBL in E. coli in many parts of the world (Rossolini et al, 2008), classical TEM and SHV ESBLs are still dominant in the USA (Bush, 2008). Members of the CTX-M-1 and CTX-M-9 clusters have repeatedly been reported in Enterobacteriaceae since the first finding of CTX-M-14 in clinical isolates of Shigella sonnei, E. coli and Klebsiella pneumoniae in 2001 (Pai et al, 2001). A nationwide survey in 2003 reported 23/246 clinical isolates (9.3 %) of E. coli with an ESBL phenotype, and only 8 of these had CTX-M enzymes (Ryoo et al, 2005)
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