Johns Hopkins Antibiotic (ABX) Guide

Acinetobacter baumannii


  • Aerobic gram-negative coccobacillus or rod, often mistaken for Neisseria or Moraxella on Gram stain.
  • Common in environment (water, soil) and hospital (catheters, lotions, ventilation equipment).
  • Grows on standard agar media.
  • A. baumannii is the major species of Acinetobacter.
    • Occasional other species include: A. calcoaceticus, A. lwoffi, A. junii, A. johnsonii and A. baylyi.
    • Low grade pathogen affecting compromised hosts (immunosuppression, post-surgical, ventilator-associated pneumonia, burn wounds, ICU pts, device-associated infections and malnutrition).


  • An increasingly important global, pan-resistant GNB nosocomial pathogen.
  • Clearly pathogenic when recovered from blood and normally sterile body sites.
  • Risks: hospitalization, ICU, surgery, antibiotic exposure and catheters.
  • May cause nosocomial epidemics from contaminated common sources, e.g., ventilation equipment, catheters, etc.
  • Diagnosis by standard aerobic bacterial culture.
  • Isolation often meaningless (representing colonization) unless from:
    • Normally sterile site
    • Found as a dominant pathogen in moderate or heavy growth from potentially contaminated site(s)
    • Part of an outbreak
    • OR have good clinical correlation


  • Usually a cause of nosocomial infections.
  • Pneumonia, nosocomial:especially ventilator-associated.
  • Septicemia: often catheter-associated, or consequence of HAP or VAP.
  • Wounds: burns, war wounds acquired (Iraq), natural disasters (hurricanes/earthquakes).
  • Rare: meningitis (post-neurosurgical), liver abscess, endocarditis, urinary tract infections, brain abscess.
  • Community-acquired: reports from Iraqi war theater, one major report from New Zealand.




  • Notify infection control.
  • Emphasize barrier precautions and hand washing.
  • Identify common source: usual suspects include water, ventilators, catheters, endoscopes, feeding tubes, etc.

Selected Drug Comments




Aminoglycosides have variable in vitro activity; amikacin is the most predictably active.


Sulbactam is the active component but available only as in combination with ampicillin (Unasyn). Usual dose is ≥6 gm/d sulbactam.

Cefepime and other beta-lactams

Beta-lactams are often resistant due to beta-lactamases. 1st & 2nd generation cephalosporins and anti-pseudomonal penicillins are usually not active. Most likely with in vitro activity: piperacillin/tazobactam, cefepime, ceftriaxone or cefotaxime.


Fluoroquinolones are usually not active or develop resistance during use, and may promote multiply-resistant strains.


Colistin is virtually always active in vitro, but historical experience has been limited by toxicity. More recent reports suggest lower rates of nephrotoxicity even when used in combination with aminoglycosides. Aerosolization of colistin is an option in some patients with pneumonia.


Usually active in vitro, although some strains are resistant. This drug (or meropenem or doripenem) is usually preferred for serious infections involving A. baumannii when sensitivity test results are unknown. Imipenem is usually active in vitro, although some strains now produce carbapenemases.


This is the most active tetracycline, more active than tigecycline. Should show sensitivity in vitro; resistance to tetracycline in of itself is not valid.


Beta-lactams are often inactive due to beta-lactamases: 1st & 2nd generation cephalosporins and anti-pseudomonal penicillins usually not active, but piperacillin/tazobactam is the most likely if at all.


(Tygacil) Tigecycline is the first glycylcycline, a relative of tetracycline. It has broad spectrum activity including many resistant Gram-negative pathogens, MRSA and VRE. It may be an alternative for highly-resistant Acinetobacter infections.

Combination therapy

Colistin + rifampin, sulbactam + carbapenem, colistin + carbapenem--each combination reported in use; no clear conclusions on utility of these approaches.


  • Acinetobacter has become major nosocomial pathogen, especially as a multiply resistant GNB in ICU.
  • Major culture sources: blood, respiratory secretions, wounds and urine.
  • Nosocomial pathogen that colonizes skin, dry surfaces and water, including hand lotion, ventilation equipment and catheters.
  • Important pathogen in war (Iraq) & disasters (tsunami).
  • Combination therapies: colistin + rifampin, sulbactam + carbapenem, colistin + carbapenem reported in use; no clear conclusions on utility of these approaches.

Basis for recommendation[Top]

  1. Fishbain J, Peleg AY: Treatment of Acinetobacter infections. Clin Infect Dis 51:79, 2010  [PMID:20504234]

    Comment: This report is the source document for antibiotic recommendations reported here.


  1. Kwa AL et al: Nebulized colistin in the treatment of pneumonia due to multidrug-resistant Acinetobacter baumannii and Pseudomonas aeruginosa. Clin Infect Dis 41:754, 2005  [PMID:16080101]

    Comment: 21 patients with pneumonia were given nebulized colistin. Overall clinical and microbiological response rates were 57% and 86% respectively.
    Rating: Important

  2. Jawad A et al: Survival of Acinetobacter baumannii on dry surfaces: comparison of outbreak and sporadic isolates. J Clin Microbiol 36:1938, 1998  [PMID:9650940]

    Comment: A. baumannii accounts for most nosocomial outbreaks of Acinetobacter infections. These organisms may survive on dry surfaces for 21-32 days. Outbreak strains tend to be multiply-resistant - resistant to ciprofloxacin, cefotaxime, ceftriaxone, cefepime, aminoglycosides.

  3. Scheetz MH et al: In vitro activities of various antimicrobials alone and in combination with tigecycline against carbapenem-intermediate or -resistant Acinetobacter baumannii. Antimicrob Agents Chemother 51:1621, 2007  [PMID:17307973]

    Comment: A. baumannii strains resistant to carbapenems (n=93) showed 95% were sensitive to tigecycline , and 88% were sensitive to minocycline.
    Rating: Important

  4. Grupper M et al: Attributable mortality of nosocomial Acinetobacter bacteremia. Infect Control Hosp Epidemiol 28:293, 2007  [PMID:17326019]

    Comment: A case control study of 52 patients with A. baumannii bacteremia showed a mortality rate of 56% and an attributable mortality of 37%.

  5. Gounden R et al: Safety and effectiveness of colistin compared with tobramycin for multi-drug resistant Acinetobacter baumannii infections. BMC Infect Dis 9:, 2009  [PMID:19272139]

    Comment: A retrospective response showing favorable results with colistin in terms of safety and efficacy.
    Rating: Important

  6. Luyt CE et al: Aerosolized antibiotics to treat ventilator-associated pneumonia. Curr Opin Infect Dis 22:154, 2009  [PMID:19276883]

    Comment: Authorities in VAP provide guidance on use of aerosolized colistin.
    Rating: Important

  7. Davies TA et al: Longitudinal survey of carbapenem resistance and resistance mechanisms in Enterobacteriaceae and non-fermenters from the USA in 2007-09. J Antimicrob Chemother 66:2298, 2011  [PMID:21775338]

    Comment: Findings are based on sensitivity tests of 994 strains of A. baumannii from US 2007-09. This showed doripenem sensitivity was 63%, significantly lower than imipenem and meropenem. The most common A. baumannii resistance mechanism was the OXA-23/24 carbapenemases. Metallo-beta-lactamases were found < 0.1%.
    Rating: Important

  8. Esterly JS et al: Impact of carbapenem resistance and receipt of active antimicrobial therapy on clinical outcomes of Acinetobacter baumannii bloodstream infections. Antimicrob Agents Chemother 55:4844, 2011  [PMID:21825287]

    Comment: Retrospective review of 79 patients with A. baumannii bacteremia including 37 with carapenem-resistant strains. Those with resistant strains did not have a higher mortality rate or longer time to becoming afebrile. Survival favored rceipt of an active drug (94% vs. 74%); survival was reduced with use of colistin.
    Rating: Important

  9. Corbella X et al: Relevance of digestive tract colonization in the epidemiology of nosocomial infections due to multiresistant Acinetobacter baumannii. Clin Infect Dis 23:329, 1996  [PMID:8842272]

    Comment: Fecal flora analysis showed A. baumannii colonization in 77 (41%) of 189 consecutive admissions to an ICU in Barcelona. Of these 77 patients, 25% had clinical infections with this organism compared to 5% of those without fecal colonization. The authors concluded that the GI tract was a major epidemic reservoir.

  10. Maragakis LL, Perl TM: Acinetobacter baumannii: epidemiology, antimicrobial resistance, and treatment options. Clin Infect Dis 46:1254, 2008  [PMID:18444865]

    Comment: Major ICU pathogen and cause of outbreaks of bacteremia, pneumonia, meningitis UTIs and wound infections. This pathogen survives long periods n a wide range of environmental conditions. Most active drugs are carbapenems, colistin, amikacin and cefepime.

  11. Jain R, Danziger LH: Multidrug-resistant Acinetobacter infections: an emerging challenge to clinicians. Ann Pharmacother 38:1449, 2004  [PMID:15280512]

    Comment: Medicine search shows A. baumannii has emerged as a worldwide major nosocomial pathogen which is often resistant to all standard antibiotics. This results in reappraisal of old agents - colistin polymyxin and ampicillin-sulbactam.

  12. Pachón-Ibáñez ME et al: Activity of tigecycline (GAR-936) against Acinetobacter baumannii strains, including those resistant to imipenem. Antimicrob Agents Chemother 48:4479, 2004  [PMID:15504889]

    Comment: Of 49 Acinetobacter baumannii isolates, including those resistant to imipenem, 92% were sensitive to tigecycline. This in vitro study suggested that the drug had bacteriostatic rather than bacteriocidal activity.

  13. Maragakis LL et al: An outbreak of multidrug-resistant Acinetobacter baumannii associated with pulsatile lavage wound treatment. JAMA 292:3006, 2004  [PMID:15613669]

    Comment: Outbreak included 11 patients who got Acinetobacter infections from a contaminated pulsatile wound debriding device.

  14. Lortholary O et al: Nosocomial acquisition of multiresistant Acinetobacter baumannii: risk factors and prognosis. Clin Infect Dis 20:790, 1995  [PMID:7795075]

    Comment: Report of 25 cases of meningitis due to Acinetobacter baumannii. Most were patients with indwelling ventriculostomy tubes or CSF fistulae who were receiving antibiotics. There were 3 deaths. The most active antibiotics (active vs >21/25 strains): imipenem, minocycline, ciprofloxacin and amikacin.

  15. Siegman-Igra Y et al: Nosocomial acinetobacter meningitis secondary to invasive procedures: report of 25 cases and review. Clin Infect Dis 17:843, 1993  [PMID:8286623]

    Comment: Report of 25 cases of meningitis due to Acinetobacter baumannii. Most were patients with indwelling ventriculostomy tubes or CSF fistulae who were receiving antibiotics. There were 3 deaths. The most active antibiotics (active vs >21/25 strains): imipenem, minocycline, ciprofloxacin and amikacin.

  16. Tsakris A et al: Clusters of imipenem-resistant Acinetobacter baumannii clones producing different carbapenemases in an intensive care unit. Clin Microbiol Infect 14:588, 2008  [PMID:18397334]

    Comment: Report shows A. baumannii clusters with different carbapenemase genes causing severe infections.

  17. Rhomberg PR et al: Antimicrobial resistance rates and clonality results from the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) programme: report of year five (2003). Diagn Microbiol Infect Dis 49:273, 2004  [PMID:15313533]

    Comment: Results with 2,848 GNB isolates in 2003 shows meropenem/imipenem active vs 96%, cefepime 94%, tobramycin 92%, pip-tazo 90%, ceftazidime 90%. Clonally-based resistance to carbapenems was noted with Klebsiella and Acinetobacter baumannii.

  18. Davis KA et al: Multidrug-resistant Acinetobacter extremity infections in soldiers. Emerg Infect Dis 11:1218, 2005  [PMID:16102310]

    Comment: Review of 23 soldiers wounded in Iraq with subsequent wound cultures yielding Acinetobacter: 18 osteomyelitis, 2 burn infections & 3 deep wound infections. All recovered with antibiotic treatment.

  19. Hiransuthikul N et al: Skin and soft-tissue infections among tsunami survivors in southern Thailand. Clin Infect Dis 41:e93, 2005  [PMID:16231248]

    Comment: Review of 641 wound infections in 305 tsunami survivors showed A. calcoaceticus, A. baumannii accounted for 26 (4%). The most common causes were ascribed to Aeromonas (23%) and coliforms (51%).

  20. Bishburg E, Bishburg K: Minocycline--an old drug for a new century: emphasis on methicillin-resistant Staphylococcus aureus (MRSA) and Acinetobacter baumannii. Int J Antimicrob Agents 34:395, 2009  [PMID:19665876]

    Comment: Review of minocycline for Acinetobacter -- the drug is old, cheap, IV or po and the best in class for MRSA and A. baumannii.
    Rating: Important

  21. Sebeny PJ, Riddle MS, Petersen K: Acinetobacter baumannii skin and soft-tissue infection associated with war trauma. Clin Infect Dis 47:444, 2008  [PMID:18611157]

    Comment: Review of war wound infections in Iraq war veterans. Most had cellulitis with "peau d'orange" and overlying vesicles that progressed to bullae. Treatment was a carbapenem plus debridement.

  22. Peleg AY, Seifert H, Paterson DL: Acinetobacter baumannii: emergence of a successful pathogen. Clin Microbiol Rev 21:538, 2008  [PMID:18625687]

    Comment: Review shows A. baumannii is now a global pathogen, a major problem with antibiotic resistance, common in ICU and war wounds in Iraq.
    Rating: Important

  23. García-Garmendia JL et al: Risk factors for Acinetobacter baumannii nosocomial bacteremia in critically ill patients: a cohort study. Clin Infect Dis 33:939, 2001  [PMID:11528563]

    Comment: Risk factors in 42 cases of A. baumannii bacteremia in ICU & RR: Immunosuppression 3.0, respiratory failure 2.9, prior ICU sepsis 4.4, prior abx 2.4, and invasive procedures 1.8. All are statistically significant.

  24. Hawley JS et al: Susceptibility of acinetobacter strains isolated from deployed U.S. military personnel. Antimicrob Agents Chemother 51:376, 2007  [PMID:17043112]

    Comment: Sensitivity tests in 95 strains of A. baumannii in soldiers returning from Iraq show the following rates of sensitivity: colistin 99%, minocycline 97%, imipenem 63%, amikacin 50%, ampicillin-sulbactam 16%, ceftazidime 9%.

  25. Cefai C et al: An outbreak of Acinetobacter respiratory tract infection resulting from incomplete disinfection of ventilatory equipment. J Hosp Infect 15:177, 1990  [PMID:1969441]

    Comment: The authors describe an outbreak of ventilatory-associated pneumonia ascribed to inadequate disinfection of ventilatory equipment.

  26. Gradon JD, Chapnick EK, Lutwick LI: Infective endocarditis of a native valve due to Acinetobacter: case report and review. Clin Infect Dis 14:1145, 1992  [PMID:1600019]

    Comment: The authors present a case of Acinetobacterendocarditis and review the literature which showed 15 cases of native valve endocarditis and 6 with prosthetic valve infections. The native valve cases tended to be acute, were often associated with a maculopapular rash involving palms and soles and 5/15 (33%) were fatal.

  27. Ling ML et al: A nosocomial outbreak of multiresistant Acinetobacter baumannii originating from an intensive care unit. Infect Control Hosp Epidemiol 22:48, 2001  [PMID:11198024]

    Comment: The authors report an outbreak involving 103 patients in an 8 month period. It was controlled by closing the unit.

  28. Jellison TK, Mckinnon PS, Rybak MJ: Epidemiology, resistance, and outcomes of Acinetobacter baumannii bacteremia treated with imipenem-cilastatin or ampicillin-sulbactam. Pharmacotherapy 21:142, 2001  [PMID:11213849]

    Comment: The authors retrospectively review 48 cases of A. baumannii bacteremia at Wayne State seen from 1987 to 1999. Treatment with ampicillin-sulbactam was as effective as treatment with imipenem.

  29. Siau H et al: Acinetobacter bacteremia in Hong Kong: prospective study and review. Clin Infect Dis 28:26, 1999  [PMID:10028065]

    Comment: The authors review 18 cases of Acinetobacter bacteremia - 16/18 were A. lwoffi. An intravenous catheter led to infection in 39%.

  30. Gaynes R, Edwards JR, National Nosocomial Infections Surveillance System: Overview of nosocomial infections caused by gram-negative bacilli. Clin Infect Dis 41:848, 2005  [PMID:16107985]

    Comment: The NNIS data with 410,000 isolates showed Acinetobacter isolations in ICU pneumonia increased from 4% in 1986 to 7% in 2003.
    Rating: Important

  31. Markou N et al: Intravenous colistin in the treatment of sepsis from multiresistant Gram-negative bacilli in critically ill patients. Crit Care 7:R78, 2003  [PMID:12974973]

    Comment: This is an anecdotal experience with the 26 cases of bacteremia involving GNB resistant to all antibiotics but colistin- 20 P. aeruginosa and 6 A. baumannii. All cases received a second agent despite resistance--usually ceftazidime. The response rate was 73%. Three (14%) developed renal failure.

  32. Barnes DJ, Naraqi S, Igo JD: The role of percutaneous lung aspiration in the bacteriological diagnosis of pneumonia in adults. Aust N Z J Med 18:754, 1988  [PMID:3266552]

    Comment: This is an incredible report from New Guinea in which the microbiology of community-acquired pneumonia was systematically studied by possibly the most definitive method-transthoracic aspiration. A. baumannii was recovered in 20%.

  33. Urban C et al: Polymyxin B-Resistant Acinetobacter baumannii Clinical Isolate Susceptible to Recombinant BPI and Cecropin P1. Antimicrob Agents Chemother 45:994, 2001  [PMID:16557680]

    Comment: This is the first report of resistance by A. baumannii to polymyxin and colistin. The MIC to colistin was 48ug/ml. The other drugs in the title are experimental.

  34. Fierobe L et al: An outbreak of imipenem-resistant Acinetobacter baumannii in critically ill surgical patients. Infect Control Hosp Epidemiol 22:35, 2001  [PMID:11198020]

    Comment: This report concerns an outbreak of 17 cases of infections involving A. baumannii in a SICU illustrating the potential importance of this organism as a nosocomial pathogen, and the potential problem it poses with antibiotic resistance.

  35. Villers D et al: Nosocomial Acinetobacter baumannii infections: microbiological and clinical epidemiology. Ann Intern Med 129:182, 1998  [PMID:9696725]

    Comment: This review showed the following sites of infection in 45 cases: urine 31%, lung 27%, wounds 18%, blood 11%, CSF 4%. A major risk factor was prior treatment with a fluoroquinolone. The authors conclude A. baumannii is: 1)an important nosocomial pathogen; 2)may cause serious disease primarily in compromised host; 3)may be epidemic or endemic, esp in ICUs; 4)there may be multiply-resistant clones; 5)prior abx, esp fluoroquinolones, may be important risk factor.

  36. Falagas ME, Bliziotis IA: Pandrug-resistant Gram-negative bacteria: the dawn of the post-antibiotic era? Int J Antimicrob Agents 29:630, 2007  [PMID:17306965]

    Comment: Three bacteria are identified as potentially resistant to all antibiotics including colistin: A. baumannii, P. aeruginosaand K. pneumoniae. Resistance to colistin is now rare.

  37. Baldry S: Attack of the clones. Nat Rev Microbiol 8:, 2010  [PMID:20467444]

    Comment: Whole gene sequencing was used to show geographic dissemination of A. baumannii from military casualties in Iraq.
    Rating: Important

  38. Higgins PG et al: In vitro activities of the beta-lactamase inhibitors clavulanic acid, sulbactam, and tazobactam alone or in combination with beta-lactams against epidemiologically characterized multidrug-resistant Acinetobacter baumannii strains. Antimicrob Agents Chemother 48:1586, 2004  [PMID:15105109]

    Comment: With these agents the enhanced activity is due to intrinsic antimicrobial activity of the beta-lactamase inhibitor and not due to enhanced activity of the beta-lactam. In vitro activity of sulbactam was superior to clavulanate or tazobactam.

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