Determination of imipenem efflux-mediated resistance in Acinetobacter spp., using an efflux pump inhibitor

  • Ghazale Amiri Deparment of Biology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran
  • Maryam Abbasi Shaye Deparment of Biology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran
  • Masoumeh Bahreini Deparment of Biology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran
  • Asghar Mafinezhad Department of Microbiology, Shahid Kamyab Hospital, Mashhad University of Medical Sciences, Mashhad, Iran
  • Kiarash Ghazvini Department of Microbiology, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran
  • Mohammad Reza Sharifmoghadam Deparment of Biology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran
Acinetobacter baumannii; Acinetobacter lwoffii; Imipenem; Antibiotic resistance; Efflux pumps


Background and Objectives: In recent years, reports of Acinetobacter strains resistant to all known antibiotics have caused a great concern in medical communities. Overexpression of efflux pumps is one of the major causes of resistance in bacteria. The aim of this study was to investigate the role of efflux pumps in conferring resistance to imipenem in clinically important Acinetobacter spp; Acinetobacter baumannii and Acinetobacter lwoffii.
Materials and Methods: A total number of 46 clinical Acinetobacter isolates, including 33 A. baumannii and 13 A. lwoffii isolates, previously collected from Shahid Kamyab and Ghaem hospitals of Mashhad, Iran were used in this study. Imipenem susceptibility testing was carried out by the disc diffusion method. Imipenem minimum inhibitory concentration (MIC) for resistant Acinetobacter isolates were determined both in the presence and absence of the efflux pumps inhibitor, carbonyl cyanide 3-chlorophenylhydrazone (CCCP).
Results: Resistance to imipenem was observed in 38 isolates including 30 A. baumannii and 8 A. lwoffii isolates. Experiments in the presence of CCCP showed a 2 to 16384 fold reduction in imipenem MICs in 14 A. baumannii and 2 A. lwoffii isolates.
Conclusion: The results obtained showed high levels of resistance to imipenem and contribution of efflux pumps in conferring resistance in both Acinetobacter species in this study. Moreover, imipenem efflux mediated resistance highlights the importance of this mechanism not only in A. baumannii but also in non-baumannii Acinetobacter Spp. which have been neglected in antibiotic resistance studies.


1. Sharma R, Sharma C, Kapoor B. Antibacterial resistance: current problems and possible solutions. Indian J Med Sci 2005;59:120-129.
2. Levy SB, Marshall B. Antibacterial resistance worldwide: causes, challenges and responses. Nat Med 2004;10(12 Suppl):S122-129.
3. Falagas M, Mourtzoukou E, Polemis M, Resistance GSfSoA, Vatopoulos A. Trends in antimicrobial resistance of Acinetobacter baumannii clinical isolates from hospitalised patients in Greece and treatment implications. Clin Microbiol Infect 2007;13:816-819.
4. Peleg AY, Seifert H, Paterson DL. Acinetobacter baumannii: emergence of a successful pathogen. Clin Microbiol Rev 2008;21:538-582.
5. Thomson JM, Bonomo RA. The threat of antibiotic resistance in Gram-negative pathogenic bacteria: β-lactams in peril! Curr Opin Microbiol 2005;8:518-524.
6. Afzal-Shah M, Woodford N, Livermore DM. Characterization of OXA-25, OXA-26, and OXA-27, molecular class D β-lactamases associated with carbapenem resistance in clinical isolates of Acinetobacter baumannii. Antimicrob Agents Chemother 2001;45:583-588.
7. Sunagawa M, Matsumura H, Inoue T, Fukasawa M, Kato M. A novel carbapenem antibiotic, SM-7338 structure-activity relationships. J Antibiot (Tokyo) 1990;43:519-532.
8. Vila J, Martí S, Sanchez-Céspedes J. Porins, efflux pumps and multidrug resistance in Acinetobacter baumannii. J Antimicrob Chemother 2007;59:1210-1215.
9. Lomovskaya O, Watkins W. Inhibition of efflux pumps as a novel approach to combat drug resistance in bacteria. J Mol Microbiol Biotechnol 2001;3:225-236.
10. Padilla E, Llobet E, Doménech-Sánchez A, Martínez-Martínez L, Bengoechea JA, Albertí S. Klebsiella pneumoniae AcrAB efflux pump contributes to antimicrobial resistance and virulence. Antimicrob Agents Chemother 2010;54:177-183.
11. Abbasi Shaye M, Sharifmoghadam MMR, Bahreini M, Amiri G. Study of the role of efflux pumps in amikacin-resistant Acinetobacter isolates from teaching hospitals of Mashhad, Iran. Jundishapur J Microbiol 2018;11 (4): e12754.
12. CLSI, editor. Performance Standards for Antimicrobial Susceptibility Testing. Wayne, PA, USA: Clinical and Laboratory Standards Institute;; 2014.
13. Neonakis I, Gikas A, Scoulica E, Manios A, Georgiladakis A, Tselentis Y. Evolution of aminoglycoside resistance phenotypes of four Gram-negative bacteria: an 8-year survey in a University Hospital in Greece. Int J Antimicrob Agents 2003;22:526-531.
14. Fihman V, Lartigue M, Jacquier H, Meunier F, Schnepf N, Raskine L, et al. Appearance of aac (6′)-Ib-cr gene among extended-spectrum β-lactamase-producing Enterobacteriaceae in a French hospital. J Infect 2008;56:454-459.
15. Van Looveren M, Goossens H, Group AS. Antimicrobial resistance of Acinetobacter spp. in Europe. Clin Microbiol Infect 2004;10:684-704.
16. Gholami M, Hashemi A, Hakemi-Vala M, Goudarzi H, Hallajzadeh M. Efflux pump inhibitor phenylalanine-arginine β-naphthylamide effect on the minimum inhibitory concentration of imipenem in Acinetobacter baumannii strains isolated from hospitalized patients in Shahid Motahari Burn Hospital, Tehran, Iran. Jundishapur J Microbiol 2015;8(10): e19048.
17. Feizabadi M, Fathollahzadeh B, Taherikalani M, Rasoolinejad M, Sadeghifard N, Aligholi M, et al. Antimicrobial susceptibility patterns and distribution of blaOXA genes among Acinetobacter spp. Isolated from patients at Tehran hospitals. Jpn J Infect Dis 2008;61:274-278.
18. Hou PF, Chen XY, Yan GF, Wang YP, Ying CM. Study of the correlation of imipenem resistance with efflux pumps AdeABC, AdeIJK, AdeDE and AbeM in clinical isolates of Acinetobacter baumannii. Chemotherapy 2012;58:152-158.
19. Lin M-F, Lin Y-Y, Tu C-C, Lan C-Y. Distribution of different efflux pump genes in clinical isolates of multidrug-resistant Acinetobacter baumannii and their correlation with antimicrobial resistance. J Microbiol Immunol Infect 2017;50:224-231.
How to Cite
Amiri G, Shaye M, Bahreini M, Mafinezhad A, Ghazvini K, Sharifmoghadam MR. Determination of imipenem efflux-mediated resistance in Acinetobacter spp., using an efflux pump inhibitor. Iran J Microbiol. 11(5):368-372.
Original Article(s)