Microbiology Spectrum (Jun 2024)

First report of the chromosomal integration of carbapenemase gene blaIMP-19 in Acinetobacter baumannii AB322: the legacy of integron in phage-plasmid?

  • Yung-Luen Shih,
  • Carl Jay Ballena Bregente,
  • Pek Kee Chen,
  • Tran Thi Dieu Thuy,
  • Yu-Chen Chen,
  • Han-Yueh Kuo,
  • Hsu-Feng Lu,
  • Cheng-Yen Kao

DOI
https://doi.org/10.1128/spectrum.00382-24
Journal volume & issue
Vol. 12, no. 6

Abstract

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ABSTRACT Integration of carbapenemase gene blaIMP into the chromosome of carbapenem-resistant Acinetobacter baumannii (CRAB) has not been reported. The aim of this study was to explore the genomic characteristics of CRAB AB322 isolated from a Taiwanese patient diagnosed with bacteremia in 2011, whose chromosome harbors blaIMP-19. Disk diffusion and broth microdilution were employed to analyze the antimicrobial susceptibility of AB322 to 14 antimicrobials. Nanopore whole-genome sequencing platform was utilized for AB322 genome sequencing, and conjugation was further performed to investigate the transferability of blaIMP-19 to amikacin-resistant A. baumannii 218 (AB218) and Acinetobacter nosocomialis 254 (AN254). The results showed that AB322 was classified as multidrug-resistant A. baumannii but remained susceptible to ampicillin/sulbactam, colistin, and tigecycline. Whole-genome sequencing revealed the AB322 genome, consisting of a 4,098,985-bp chromosome, a 71,590-bp conjugative plasmid named pAB322-1, and an 8,726-bp plasmid named pAB322-2. Multilocus sequence typing analysis indicated that AB322 belonged to sequence type 1. AB322 chromosome harbored numerous acquired antimicrobial resistance genes, including aph(3′)-Ia, aadA1b, aadA1, aac(6′)-Ib3, aac (3)-Ia, blaADC-25, blaOXA-69, blaIMP-19, catA1, sul1, and tet(A), conferring resistance to β-lactams, aminoglycosides, chloramphenicol, sulfamethoxazole, and tetracyclines. Moreover, blaIMP-19 was identified to be situated within class 1 integron In240 and an incomplete PHAGE_Salmon_SJ46_NC_031129 on AB322 chromosome. However, conjugation experiments revealed that blaIMP-19 could not be transferred to AB218 and AN254 in our testing conditions. In conclusion, we first report the presence of chromosomal-integrated blaIMP-19 in CRAB, possibly mediated by integron. The future dissemination of blaIMP-19 among different species, leading to carbapenem resistance dissemination, requires close monitoring.IMPORTANCEThe horizontal transfer of antimicrobial-resistant genes is crucial for the dissemination of resistance, especially as Acinetobacter baumannii has emerged as a clinically significant pathogen. However, in this study, we first report the integration of the blaIMP-19 gene into the chromosome of A. baumannii, and such horizontal transfer may be associated with integron-phage elements. Additionally, it is possible that these DNA fragments carrying antimicrobial-resistant genes could further spread to other pathogens by moving horizontally onto conjugative plasmids.

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