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Year : 2015  |  Volume : 33  |  Issue : 4  |  Page : 614--615

Novel sequence type 435 with plasmid-borne New Delhi metallo-β-lactamase-1 in Acinetobacter baumannii

M Li1, J Liu2, X Yu3, Y Sun1, Y Zhang1, C Ma1, J Ye1, T Zhou1,  
1 Department of Clinical Laboratory, The First Affiliated Hospital of Wenzhou Medical University, Wenzhou, Zhejiang Province, China
2 Department of Clinical Laboratory, The Maternal and Child Health Hospital of Hunan Province, Hunan, Zhejiang Province, China
3 Department of Medical Lab Science, School of Laboratory Medicine and Life Science, Wenzhou Medical University, Wenzhou, Zhejiang Province, China

Correspondence Address:
T Zhou
Department of Clinical Laboratory, The First Affiliated Hospital of Wenzhou Medical University, Wenzhou, Zhejiang Province
China

How to cite this article:
Li M, Liu J, Yu X, Sun Y, Zhang Y, Ma C, Ye J, Zhou T. Novel sequence type 435 with plasmid-borne New Delhi metallo-β-lactamase-1 in Acinetobacter baumannii.Indian J Med Microbiol 2015;33:614-615

How to cite this URL:
Li M, Liu J, Yu X, Sun Y, Zhang Y, Ma C, Ye J, Zhou T. Novel sequence type 435 with plasmid-borne New Delhi metallo-β-lactamase-1 in Acinetobacter baumannii. Indian J Med Microbiol [serial online] 2015 [cited 2020 Aug 14 ];33:614-615
Available from: http://www.ijmm.org/text.asp?2015/33/4/614/167340

Full Text

Dear Editor,

Carbapenem-resistance Acinetobacter baumannii (CRAB) has become a major public health hazard in recent years.[1] Since a novel carbapenemase named New Delhi metallo-β-lactamase-1 (NDM-1, encoded by blaNDM-1) was first described in 2009,[2] NDM-1-producing organisms have been reported worldwide and represent a new and significant challenge in the treatment of infectious diseases.[3],[4] Here, we analyzed the molecular characteristics and epidemiology of two NDM-1-producing A. baumannii isolates recovered from a teaching hospital in Wenzhou, Southern China.

Seven hundred and fifty-six carbapenem-resistant A. baumannii clinical isolates were collected from the First Affiliated Hospital of Wenzhou Medical University, among which two strains were found to harbour blaNDM-1 by polymerase chain reaction (PCR) and sequencing, named A. baumannii B2214 and B2226. They were isolated from sputum of two senior male patients, who received care at the respiratory intensive care unit (RICU) in February 2009. Previous reports revealed that international travel, especially to the Indian subcontinent, was responsible for the dissemination of blaNDM-1.[5] However, the two patients harbouring NDM-1-producing A. baumannii had never travelled aborad. By agar dilution method, the two NDM-1-producing A. baumannii isolates exhibited a phenotype of highly resistant to ceftriaxone, ceftazidime, imipenem, meropenem, aztreonam, tetracycline and gentamicin, while remained susceptible to ciprofloxacin, levofloxacin, tobramycin and polymyxin B. The modified Hodge test (MHT) and ethylenediaminetetraacetic acid (EDTA)-disk synergy tests were both positive for B2214 and B2226. PCR and sequencing results showed that in addition to blaNDM-1, both strains also carried blaIMP-1, blaADC, blaOXA-23, blaOXA-51-like, tetA and tetB. We inferred that the coexistence of multiple resistant genes would be the mechanism for high-level resistance to various kinds of antibiotics in A. baumannii isolates. Thus, a considerable number of antibiotics could not be effective for the control of infections caused by NDM-1 strains. Moreover, after S1-pulsed-field gel electrophoresis (PFGE) assay and Southern blot hybridization, we found that blaNDM-1 was located on a ~55–78 kb plasmid. Conjugation experiment showed that blaNDM-1 and tetA can be successfully transferred to Escherichia coli J53 (transconjugants were designated as J-B2214 and J-B2226). Susceptibility testing revealed that both the transconjugants showed resistance or decreased susceptibility to cephalosporins, carbapenems and tetracycline. All the transconjugants stably maintained the blaNDM-1-containing plasmid after ten passages in the presence of meropenem (0.5μg/ml). However, transconjugants would lose blaNDM-1 and tetA after ten passages when there was no selection pressure. Transfer frequency was higher when conjugation was performed under 37°C rather than under 4°C, 25°C or 30°C. These data displayed the potential for the spread of blaNDM through plasmid transmission among different species. With regard to genotypic relatedness, multilocus sequence typing (MLST) revealed that A. baumannii B2214 and B2226 belonged to a novel sequence types (STs), namely ST 435. Furthermore, PFGE analysis showed that the two NDM-1-producing isolates shared the same clone and were genetic unrelated with other no NDM-1-producing isolates in the same ward [Figure 1].{Figure 1}

In conclusion, this is the first report on a novel A. baumannii ST 435 harboured blaNDM-1 with blaOXA-23, blaIMP-1, tetA and tetB in China. Nevertheless, blaNDM-1 can be transferred from Acinetobacter spp. to Enterobacteriaceae and the transconjugant stably maintained the blaNDM-1-containing plasmid of A. baumannii under antibiotic selection pressure in this study. So, the rigorous infection control measures should be strengthened to prevent the horizontal transmission of blaNDM-1 among bacterial populations.

References

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