Journal List > Korean J Clin Microbiol > v.13(1) > 1038207

Roh, Kim, Yum, Yong, Jeong, Lim, Lee, Cho, Lee, and Chong: Carbapenem Resistance Mechanisms and Molecular Epidemiology of Acinetobacter spp. from Four Hospitals in Seoul and Gyeonggi Province in 2006

Abstract

Background

Increasing numbers of Acinetobacter spp. resistant to multiple drugs, including carbapenem, has been a serious problem. The aims of this study were to determine carbapenem resistance patterns and mechanisms, as well as to study the molecular epidemiology of Acinetobacter spp.

Methods

Clinical isolates of Acinetobacter spp. were collected from May to November in 2006. Antimicrobial susceptibility testing was performed using CLSI disk diffusion and agar dilution methods. Metallo-β-lactamase-and OXA carbapenemase-producing isolates were detected by PCR. Carbapenem resistance and hydrolytic activities were compared according to OXA type and presence of ISAba1. Pulsed-field gel electrophoresis (PFGE) was performed to determine the epidemiologic features.

Results

The imipenem non-susceptible rates were variable from 10% to 67%. Among 151 isolates carrying blaOXA-51-like, 75 isolates carried both blaOXA-51-like and ISAba1, and 25 isolates had both blaOXA-51-like, blaOXA-23-like, and ISAba1. Carbapenem MICs of both blaOXA-51-like and ISAba1-carrying isolates were higher than those with blaOXA-51-like only. Carbapenem MICs of blaOXA-23-like-carrying isolates were higher than those with both blaOXA-51-like and ISAba1. Both blaOXA-51-like and ISAba1-carrying isolates and blaOXA-51-like, blaOXA-23-like, and ISAba1-carrying isolates demonstrated higher hydrolysis activities in oxacillin and carbapenems. Most of the tested isolates were susceptible to tigecycline, and all of them were susceptible to colistin. Pulsed-field gel electrophoresis suggested that there had been several outbreaks of blaOXA-23-like and blaOXA-51-like-positive strains.

Conclusion

Carbapenem non-susceptible Acinetobacter isolates and OXA carbapenemase-producing isolates were prevalent. Dissemination of blaOXA-harboring isolates may make it difficult to treat infections due to carbapenem-resistant Acinetobacter spp. Further surveillance studies are required to prevent the spread of carbapenem resistance.

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Fig. 1.
Pulsed-field gel electrophoresis (PFGE) patterns of SmaI-restricted genomic DNA of Acinetobacter spp. isolates. (A) Isolates having blaOXA-51 and ISAbaI. Lane I to IX, different clones from 4 hospitals; and (B) isolates having both blaOXA-51, blaOXA-23 and ISAbaI. Lane I-1 to IV, different clones from 4 hospitals; Molecular size (ladder marker) is given in kilobases.
kjcm-13-27f1.tif
Table 1.
Primers used for detection and sequencing of the metallo-β-lactamase, OXA carbapenemase, and ISAba1 genes
Target Primer name Primer sequence (5' to 3') Reference
blaVIM-like VIM-F GAT GGT GTT TGG TCG CAT A [14]
  VIM-R CGA ATG CGC AGC ACC AG  
blaIMP-like IMP-F GGA ATA GAG TGG CTT AAY TCT C [14]
  IMP-R CCA AAC YAC TAS GTT ATC T  
blaSIM-like SIM-F TAC AAG GGA TTC GGC ATC G [14]
  SIM-R TAA TGG CCT GTT CCC ATG TG  
ISAba1 ISAba1-F CAC GAA TGC AGA AGT TG [10]
  ISAba1-R CGA CGA ATA CTA TGA CAC  
  ISAba1end-F CAT TGA GAT GTG TCA TAG (Sequencing only)  
blaOXA-23-like OXA-23-F GAT CGG ATT GGA GAA CCA GA [15]
  OXA-23-R ATT TCT GAC CGC ATT TCC AT  
blaOXA-24-like OXA-24-F GG T TAG TTG GCC CCC TTA AA [15]
  OXA-24-R AGT TGA GCG AAA AGG GGA TT  
blaOXA-51-like OXA-51-F TAA TGC TTT GAT CGG CCT TG [15]
  OXA-51-R TGG ATT GCA CTT CAT CTT GG  
blaOXA-58 OXA-58-F AAG TAT TGG GGC TTG TGC TG [15]
  OXA-58-R CCC CTC TGC GCT CTA CAT AC  
Table 2.
Characteristics of OXA carbapenemase-producing Acinetobacter spp. by hospitals
Hospital No. of isolates No. of IMP-NS, PCR tested No. of IMP-S, PCR tested blaOXA-51 alleles blaIMP-1 blaVIM-2 blaSIM-1 blaOXA-51-like without ISAba1 (Group I) blaOXA-51-like with ISAba1 (Group II) blaOXA-51-like with blaOXA-23-like (Group III)
A 77 39 10 Pos (40) 5 34 1
        Neg (9) 0 2 4
B 191 26 10 Pos (29) 28 1 0
        Neg (7) 7 0 0
C 102 68 7 Pos (73) 13 39 21
        Neg (2) 1 0 0
D 59 6 5 Pos (9) 5 1 3
        Neg (2) 1 0 0
Total 429 139 32 Pos (151) 51 75 25
        Neg (20) 9 2 4

Abbreviations: IMP-NS, imipenem non-susceptible; IMP-S, imipenem susceptible; Pos, positive; Neg, negative.

Table 3.
Antimicrobial susceptibility of blaOXA-51-like-carrying Acinetobacter spp. isolates with or without ISAba1
Antimicrobial agent blaOXA-51-like without ISAba1 (Group I) blaOXA-51-like with ISAba1 (Group II) blaOXA-51-like and blaOXA-23-like with ISAba1 (Group III)
MIC (μg/mL) range / % non-susceptible MIC50 MIC90 MIC (μg/mL) range / % non-susceptible MIC50 MIC90 MIC (μg/mL) range / % non-susceptible MIC50 MIC90
Imipenem 0.25∼8/25 4 8 2∼16/99 8 8 8∼64/100 16 32
Meropenem 0.25∼64/74 8 16 4∼128/99 16 32 16∼64/100 32 64
Ceftazidime 2∼>128/90 128 >128 64∼>128/100 128 >128 128∼>128/100 128 >128
Cefepime 4∼>128/94 32 128 16∼>128/100 32 >128 32∼>128/100 128 >128
Tigecycline 0.25∼4/6 2 2 0.5∼4/11 2 4 1∼2/0  2 2
Colistin 0.5∼2/0 1 2 0.5∼2/0 1 1 1∼2/0  2 2
Table 4.
Hydrolytic activities (relative %) of various OXA-carbapene-mase-producing strains
Strain (Group) K19, blaOXA-51-like without ISAba1 (Group I) K28, blaOXA-51-like with ISAba1 (Group II) K106, blaOXA-51-like and blaOXA-23-like with ISAba1 (Group III)
Penicillin 100 100 100
Oxacillin <1 25 19
Cephalothin 62 55 35
Imipenem 1 3 2
Meropenem <1 1 1
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