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KMID : 0829320130160030120
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Korean Journal of Clinical Microbiology
2013 Volume.16 No. 3 p.120 ~ p.125
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Loss of blaVIM-2 and blaIMP-1 during the Storage of Gram-Negative Bacilli, Antimicrobial Susceptibility of the Gene-Lost Strain, and Location of the Gene in the Cell
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Lim Young-Sik
Lee Yang-Soon
Seo Young-Hee
Yum Jong-Hwa
Yong Dong-Eun
Lee Kyung-Won
Chong Yun-Sop
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Abstract
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Background: Gram-negative bacilli can be stored in cystine tryptic agar (CTA) at room temperature for over
1 year, but we experienced a loss of imipenem resistance among VIM-2-producing isolates. The aims of this
study were to determine the frequency of loss of IMP-1 and VIM-2 genes during storage in CTA at room temperature
and to document any change in the MIC of antimicrobial agents and the location of the gene.
Methods: Bacteria were isolated from clinical specimens at Severance Hospital collected from 1995-2000.
Modified Hodge and double disk synergy tests were performed for screening of MBL-production isolates, and blaIMP-1 and blaVIM-2 were detected by PCR. Loss of resistance was tested in CTA at room temperature. PFGE and hybridization using a blaVIM-2 probe were carried out to determine the location of the VIM-2 gene.
Results: When VIM-2- and IMP-1-producing strains of eight P. aeruginosa and two Acinetobacter spp. were stored in CTA at room temperature, some isolates lost imipenem resistance after 3 days and 90% lost resistance after 15 weeks. Loss of resistance genes resulted in a decrease of the MIC of imipenem from 32-128 μg/mL to 0.5-8 μg/mL for P. aeruginosa, and from 32 μg/mL to 0.25-4 μg/mL for Acinetobacter spp. Hybridization of I-CeuI and S1-digested and PFGE
suggested that VIM-2 genes are located on approximately 50-100 kb or 400 kb plasmids.
Conclusion: Isolates may lose resistance genes when stored in CTA at room temperature. Therefore, it is
necessary for MBL-production tests including the Modified Hodge test and double disk synergy test and detection of MBL genes.
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KEYWORD
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Carbapenems, , Metallo-β-lactamase, Resistance loss
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