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KMID : 1100720130330050353
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Annals of Laboratory Medicine
2013 Volume.33 No. 5 p.353 ~ p.355
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An Increase in the Clinical Isolation of Acquired AmpC β-Lactamase-Producing Klebsiella pneumoniae in Korea from 2007 to 2010
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Park Min-Jeong
Kim Taek-Kyung
Song Won-Keun
Kim Jae-Seok
Kim Han-Sung
Lee Ja-Cob
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Abstract
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We investigated the occurrence and genetic basis of AmpC β-lactamase (AmpC)-mediated antibiotic resistance, by examining Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis isolates at a university hospital, from 2007 to 2010. The ampC genes were detected by multiplex AmpC PCR, and AmpC-positive strains were subjected to DNA sequencing. Extended-spectrum β-lactamase (ESBL) production was assessed using the ESBL disk test based on the utilization of boronic acid. Carbapenem-resistant isolates were further investigated by the modified Hodge test, a carbapenemase inhibition test and SDSPAGE experiments. AmpC expression was detected in 1.6% of E. coli (39 DHA-1, 45 CMY- 2, and 1 CMY-1) isolates, 7.2% of K. pneumoniae (39 DHA-1, 45 CMY-2, and 1 CMY-1) isolates, and 2.5% of P. mirabilis (8 CMY-2 and 1 CMY-1) isolates. Of the 198 acquired AmpC producers, 58 isolates (29.3%) also produced an ESBL enzyme. Among the acquired AmpC-producing K. pneumoniae isolates, the minimum inhibitory concentration (MIC) MIC50/MIC90 values for cefoxitin, cefotaxime, cefepime, imipenem, and meropenem were >32/>32, 16/>32, 1/16, 0.25/0.5, and <0.125/0.125 μg/mL, respectively. The MIC values for carbapenem were ≥2 μg/mL for 2 K. pneumoniae isolates, both of which carried the blaDHA-1 gene with a loss of OmpK36 expression, but were negative for carbapenemase production. The acquisition of AmpC-mediated resistance in K. pneumoniae isolates increased, as did the proportion of AmpC and ESBL co-producers among the hospital isolates. The accurate identification of isolates producing AmpCs and ESBLs may aid in infection control and will assist physicians in selecting an appropriate antibiotic regimen.
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KEYWORD
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Klebsiella pneumoniae, AmpC β-lactamases, DHA-1, CMY-2
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