Identification of a novel ciprofloxacin tolerance gene, aciT, which contributes to filamentation in Acinetobacter baumannii

Varsha Naidu, Bhumika Shah, Karthik S. Kamath, Arthur Chien, Stephanie Nagy, Alaska Pokhrel, Mark Molloy, Karl A. Hassan, Ian T. Paulsen*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)
57 Downloads (Pure)


Fluoroquinolones are one of the most prescribed broad-spectrum antibiotics. However, their effectiveness is being compromised by high rates of resistance in clinically important organisms, including Acinetobacter baumannii. We sought to investigate the transcriptomic and proteomic responses of the clinical A. baumannii strain AB5075-UW upon exposure to subinhibitory concentrations of ciprofloxacin. Our transcriptomics and proteomics analyses found that the most highly expressed genes and proteins were components of the intact prophage phiOXA. The next most highly expressed gene (and its protein product) under ciprofloxacin stress was a hypothetical gene, ABUW_0098, named here the Acinetobacter ciprofloxacin tolerance (aciT) gene. Disruption of this gene resulted in higher susceptibility to ciprofloxacin, and complementation of the mutant with a cloned aciT gene restored ciprofloxacin tolerance to parental strain levels. Microscopy studies revealed that aciT is essential for filamentation during ciprofloxacin stress in A. baumannii. Sequence analysis of aciT indicates the encoded protein is likely to be localized to the cell membrane. Orthologs of aciT are found widely in the genomes of species from the Moraxellaceae family and are well conserved in Acinetobacter species, suggesting an important role. With these findings taken together, this study has identified a new gene conferring tolerance to ciprofloxacin, likely by enabling filamentation in response to the antibiotic.

Original languageEnglish
Article numbere01400
Pages (from-to)1-9
Number of pages9
JournalAntimicrobial Agents and Chemotherapy
Issue number6
Publication statusPublished - May 2021

Bibliographical note

Copyright the Author(s) 2021. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.


  • Acinetobacter
  • Antibiotic resistance
  • Ciprofloxacin
  • Filamentation
  • Fluoroquinolone
  • Pathogen


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