• Antibiotic Resistance Mechanisms in Acinetobacter baumannii: A Growing Threat to Healthcare Systems Worldwide
  • Saba Soradi Mahkan,1,* Ghazaleh Esfandiari,2 Mohammad amin Saghi,3
    1. Department of Biology, Faculty of Basic Sciences, Islamic Azad University, Mashhad, Iran
    2. Department of Biology, Faculty of Basic Sciences, Islamic Azad University, Mashhad, Iran
    3. Department of Biology, Faculty of Basic Sciences, Islamic Azad University, Mashhad, Iran


  • Introduction: Acinetobacter baumannii is included in the Moraxellaceae family [4] It is an aerobic, non-fermentative, Gram-negative, rod-shaped bacterium.It is widely found in water, soil, and air [1]. A. baumannii has the ability to colonize various sites of healthy humans for example the skin, conjunctiva, oral cavity, respiratory tract, gastrointestinal tract, and genitourinary tract and this bacteria causes nosocomial infections [1]. It is mostly known for its ability to cause diseases in hospitalized patients [4]. A. baumannii has acquired extensive antimicrobial resistance, associated with a higher mortality rate among infected patients compared with other non-baumannii species [2]. Resistance mechanisms can be transmitted from one bacterium to the other either longitudinally, when inherited from relatives, or horizontally, with the help of plasmids [2]. The battle against A. baumannii is not confined to the microcosm of microbiological research or hospital wards; it is a broader public health problem that needs a coordinated ,global response [4]. This article attempts to summarize antibiotic resistance mechanisms in A. baumannii.
  • Methods: This review article was carried out by searching the PubMed database for relevant studies from the years 2020 to 2025. The search terms employed included: "Acinetobacter baumannii", "antibiotic resistance", "multidrug resistance", "ArmA", "OXA", and "efflux pumps". English language articles that addressed molecular resistance mechanisms of isolates of A. baumannii were selected. Data were gathered and summarized by antibiotic class and resistance mechanism.
  • Results: Aminoglycosides: Resistance to certain aminoglycosides including gentamicin, amikacin, and tobramycin in A. baumannii is mostly mediated by the ArmA. Strains that produce ArmA show a high level of resistance to these [2]. Carbapenem: Carbapenem resistance is being reported at an increasing rate ,which is primarily due to the production of OXA-type β-lactamases. These cause resistance to oxacillin and carbapenems but do not have an impact on cephalosporins [2]. Cephalosporins: Resistance to cephalosporins is mainly caused by other bla type gene such as blaAmpC, which inactivates these antibiotics [2]. Fluoroquinolone: Fluoroquinolone resistance mechanism includes substitutions in the quinolone resistance-determining regions (QRDRs) of DNA topoisomerase IV and DNA gyrase ,which hinder the binding of fluoroquinolones to their target proteins; Moreover, Over expression of efflux active pumps can also cause resistance to some extent and increase resistance in strains with RDRQ substitution [2]. Tetracycline and Chloramphenicol: Efflux pump genes are either carried on mobile elements (e.g., TetA, CmlA) or chromosomally; in both cases, overexpression can cause intrinsic or acquired resistance [3].
  • Conclusion: The continuous rise of A. baumannii as a highly problematic nosocomial pathogen represents a major challenge for contemporary healthcare systems globally [5]. Acinetobacter baumannii is an emerging nosocomial pathogen due to its ability to develop resistance to multiple antibiotics, including certain aminoglycosides (such as gentamicin, amikacin, and tobramycin .Other aminoglycosides are not discussed in this review article), Carbapenems, fluoroquinolones, tetracycline , chloramphenicol ,and cephalosporins. Resistance mechanisms like production of ArmA, OXA-type β-lactamases, and efflux pumps are all important in this resistance. Understanding of these mechanisms is crucial for the construction of impactful treatment protocols and for preventing this pathogen's widespread dissemination.
  • Keywords: Acinetobacter baumannii, antibiotic resistance, mechanisms, growing threat