Korean J Clin Microbiol.  2012 Dec;15(4):131-138. 10.5145/KJCM.2012.15.4.131.

Diversity of Integrons Carrying blaVIM-2 Cassette in Pseudomonas spp. and Acinetobacter spp.

• Yum J
• Shin HB
• Yong D
• Chong Y

• KMID: 1431809
• DOI: http://doi.org/10.5145/KJCM.2012.15.4.131

Abstract

BACKGROUND
Metallo-beta-lactamase-mediated carbapenem resistance has been increasingly reported in Pseudomonas, Acinetobacter and other Gram-negative bacilli (GNB) in many countries. A few studies showed highly variable structure of MBL-gene cassette-carrying integrons. The aim of this study was to determine the structure of blaVIM-2-carrying integrons in Pseudomonas and Acinetobacter.
METHODS
blaVIM-2-carrying GNB were isolated at a Korean hospitals during the years 1995-1999 and 2005. The size of blaVIM-2-carrying integrons was estimated by the PCR products. Representative integrons were sequenced by the dideoxy-chain termination method. The MICs of antimicrobial agents were tested by the CLSI agar dilution methods.
RESULTS
During the years 1995-1999 and 2005, the approximate size of the blaVIM-2-carrying class 1 integrons was 3-7 kb in 35 Pseudomonas isolates and 3-5 kb in 24 Acinetobacter isolates. The integrons carried one-five resistance gene cassettes in addition to the blaVIM-2 cassette. Other resistance gene cassettes found were blaOXA-1, aacA1, aac(6')-I, and aac(6')-II. Interestingly, sequences homologous to part of a putative class II intron were inserted into the recombination site of the last cassette in four of nine integrons. The class 1 integron from P. aeruginosa isolates had fused orf/IntI1 in a downstream leftward inverted repeat (IRi).
CONCLUSION
According to period, the size and structure of blaVIM-2-carrying integrons are quite variable, but an identical one is also present in a different genus, indicating high mobility of the blaVIM-2 cassette and horizontal transfer of the whole integron. We suggest that the class 1 integron containing the blaVIM-2 gene is spreading horizontally among Gram-negative bacilli and is undergoing continuous development in Korea.

Keyword

Gram-negative bacilli; Integron; Metallo-beta-lactamase

MeSH Terms

Acinetobacter
Agar
Anti-Infective Agents
Integrons
Introns
Korea
Lifting
Polymerase Chain Reaction
Pseudomonas
Recombination, Genetic
Agar
Anti-Infective Agents

Figure

• 

  Fig. 1 Comparison of the structures of variable regions of class 1 integrons determined in this study. Hatched rectangles indicate the 5'- and 3'-conserved segments (5'-CS and 3'-CS), black arrows the cassette-borne resistance genes, empty rectangles the attC sites of the cassettes, small rectangle the IRi sites of the integron, and gray circles the recombination core sites and inverse core sites. The insertion and orientation of part of putative class II intron in the recombination site of the last cassette of In106 and integron in P. putida YMC 99/10/431, P. aeruginosa YMC 95/1/704, and P. aeruginosa YMC 05/5/1103 are indicated.

• 

  Fig. 2 Deduced amino acid changes of aac(6')-I detected in this study, compared to aac(6')-I deduced amino acid reported by Nobuta et al. [10], P. aeruginosa YMC 95/1/2105 and P. putida YMC 99/10/431 had a mutation T269C and deduced amino acid change of L90S. P. aeruginosa YMC 95/1/2105 also had G298A and T512A mutations, resulting in amino acid changes of G100S and V171D. Isolates with mutations in this study: Study No. 3, 6 in Table 2. P. aeruginosa YMC 95/1/704 and P. putida YMC 99/10/431; No. 2. Acinetobacter genomospecies 3 YMC 99/11/U160; No. 4. P. aeruginosa YMC 95/1/2105.

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