Characterization of a New Integron Containing VIM-2 Metallo-beta-Lactamase Gene Cassette in an Isolate of Morganella morganii from a Urine Specimen

Kim, Taek Sang; Kim, Jong Chul; Jung, Soek Hun

Abstract

PURPOSE: The main objectives of this work were to characterize the mechanism of resistance to imipenem of Morganella morganii KU158 isolated in Busan, Korea and to analyze the structure of the integron, which carries the resistance gene that confers resistance to imipenem.
MATERIALS AND METHODS
Antimicrobial susceptibilities of M. morganii KU158 were tested by using the disk diffusion method. The modified Hodge and EDTA-disk synergy tests were performed for the screening of metallo-beta-lactamase-producing isolates. blaIMP and blaVIM genes were detected using the polymerase chain reaction (PCR) amplification. To detect the presence of the integron, the PCR method was used. The PCR product was cloned through the use of primers, 5'CS-F and 3'CS-R, and it was used to determine the sequence of the integron through the dideoxy-mediated chain termination method.
RESULTS
M. morganii KU158 was intermediately resistant to imipenem and showed a positive result for the modified Hodge and EDTA-disk synergy tests, which suggest the production of metallo-beta-lactamase, and also was positive in the PCR result for the detection of blaVIM gene. The genotype of the PCR product from the blaVIM gene was blaVIM-2. Sequencing of the 5,031 bp-cloned fragment revealed the structure of the class I integron, such as the 5'-CS element containing an Intl1 integrase gene with its own promoter region, the attI1 recombination site, and the 3'-CS element containing qacE1. The integron contained insert gene cassettes blaVIM-2, aac(6')-Ib, aadA1, "orfII", and "orfIII". The blaVIM-2 gene was located immediately downstream of the aac(6')-Ib gene.
CONCLUSIONS
M. morganii KU158 acquired the resistance to imipenem through the production of metallo-beta-lactamase VIM-2. The gradual increase in the number of VIM-2-producing bacterial species may indicate the highly mobile nature of the blaVIM-2 cassette. The spread of blaVIM-2 could compromise the future usefulness of carbapenem in treating gram-negative bacilli infections.