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Acinetobacter Infections

By Larry M. Bush, MD, Affiliate Professor of Clinical Biomedical Sciences; Affiliate Associate Professor of Medicine, Charles E. Schmidt College of Medicine, Florida Atlantic University; University of Miami-Miller School of Medicine
Maria T. Perez, MD, Associate Pathologist, Department of Pathology and Laboratory Medicine, Wellington Regional Medical Center, West Palm Beach

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Acinetobacter sp can cause suppurative infections in any organ system; these bacteria are often opportunists in hospitalized patients.

Acinetobacter are gram-negative aerobic bacilli that belong to the family Neisseriaceae. They are ubiquitous and can survive on dry surfaces for up to a month and are commonly carried on the skin of health care workers, increasing the likelihood of patients being colonized and medical equipment being contaminated. There are many species of Acinetobacter; all can cause human disease, but A. baumannii (AB) accounts for about 80% of infections.

Diseases Caused by Acinetobacter

The most common manifestations of Acinetobacter disease are

  • Respiratory infections

AB infections typically occur in critically ill, hospitalized patients. Community-acquired infections (mostly pneumonia) are more common in tropical climates. Crude death rates associated with AB infection are 19 to 54%.

The most common site for infection is the respiratory system.

Acinetobacter easily colonize tracheostomy sites and can cause community-acquired bronchiolitis and tracheobronchitis in healthy children and tracheobronchitis in immunocompromised adults. Hospital-acquired Acinetobacter pneumonias are frequently multilobar and complicated. Secondary bacteremia and septic shock are associated with a poor prognosis.

Acinetobacter sp can also cause suppurative infections (eg, abscesses) in any organ system, including the lungs, urinary tract, skin, and soft tissues; bacteremia may occur.

Rarely, these organisms cause meningitis (primarily after neurosurgical procedures), cellulitis, or phlebitis in patients with an indwelling venous catheter; ocular infections; native or prosthetic valve endocarditis; osteomyelitis; septic arthritis; or pancreatic and liver abscesses.

The significance of isolates from clinical specimens, such as respiratory secretions from intubated patients or specimens from open wounds, is difficult to determine because they often represent colonization.

Risk factors

Risk factors for Acinetobacter infection depend on the type of infection (hospital-acquired, community-acquired, multidrug resistant—see Table: Risk Factors for Acinetobacter Infection).

Risk Factors for Acinetobacter Infection

Type of Infection

Risk Factors


Fecal colonization with Acinetobacter

ICU stay

Indwelling devices

Length of hospital stay

Mechanical ventilation

Parenteral nutrition

Previous infection


Treatment with broad-spectrum antibiotics




Cigarette smoking

Chronic lung disease

Diabetes mellitus

Residence in a tropical developing country


Exposure to colonized or infected patients

Invasive procedures

Mechanical ventilation, particularly if prolonged

Prolonged hospitalization (particularly in the ICU)

Receipt of blood products

Use of broad-spectrum antibiotics (eg, 3rd-generation cephalosporins, carbapenems, fluoroquinolones)

Drug resistance

Recently, multidrug resistant (MDR) AB has emerged, particularly in ICUs in immunosuppressed patients, patients with serious underlying disorders, and patients treated with broad-spectrum antibiotics after an invasive procedure. Spread in ICUs has been attributed to colonized health care practitioners, contaminated common equipment, and contaminated parenteral nutrition solutions.


  • Typically empiric multidrug therapy for serious infections

In patients with localized cellulitis or phlebitis associated with a foreign body (eg, IV catheter, suture), removal of the foreign body plus local care is usually sufficient. Tracheobronchitis after endotracheal intubation may resolve with pulmonary toilet alone. Patients with more extensive infections should be treated with antibiotics and with debridement if necessary.

AB has long had intrinsic resistance to many antimicrobials. MDR-AB are defined as strains that are resistant to 3 classes of antimicrobials; some isolates are resistant to all. Before susceptibility results are available, possible initial options include a carbapenem (eg, meropenem, imipenem, doripenem), colistin, or a fluoroquinolone plus an aminoglycoside, rifampin, or both. Sulbactam (a beta-lactamase inhibitor) has intrinsic bactericidal activity against many MDR-AB strains. Tigecycline, a glycylcycline antibiotic, is also effective; however, borderline activity and emergence of resistance during therapy have been reported. Minocycline has in vitro activity.

Mild to moderate infections may respond to monotherapy. Traumatic wound infections can be treated with minocycline. Serious infections are treated with combination therapy—typically, imipenem, or ampicillin/sulbactam plus an aminoglycoside.

To prevent spread, health care practitioners should use contact precautions (hand washing, barrier precautions) and appropriate ventilator care and cleaning for patients colonized or infected with MDR-AB.

Key Points

  • A. baumannii (AB) accounts for about 80% of infections and tends to occur in critically ill, hospitalized patients.

  • The most common site for infection is the respiratory system, but Acinetobacter sp can also cause suppurative infections in any organ system.

  • Multidrug-resistant AB has become a problem; use multidrug treatment chosen based on susceptibility testing.

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