Acinetobacter species are gram-negative organisms that can cause suppurative infections in any organ system; these bacteria are often opportunists in patients who are hospitalized. Treatment is with multidrug therapies based on susceptibility testing.
Acinetobacter are gram-negative aerobic bacilli or coccobacilli that belong to the family Moraxellaceae. 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 Acinetobacter baumannii accounts for about 80% of infections (1). The World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) categorize carbapenem-resistant A. baumannii (CRAB) species as high-priority pathogens on their list of antibiotic-resistance threats (2).
General references
1. Wong D, Nielsen TB, Bonomo RA, et al. Clinical and pathophysiological overview of Acinetobacter infections: A century of challenges. Clin Microbiol Rev. 2017;30(1):409–447. doi:10.1128/CMR.00058-16
2. De Oliveira DMP, Forde BM, Kidd TJ, et al. Antimicrobial Resistance in ESKAPE Pathogens. Clin Microbiol Rev. 2020;33(3):e00181-19. Published 2020 May 13. doi:10.1128/CMR.00181-19
Diseases Caused by Acinetobacter
The most common manifestations of Acinetobacter disease are
Respiratory infections
A. baumannii (AB) infections typically occur in people who are critically ill and hospitalized. Community-acquired infections (mostly pneumonia) are more common in tropical climates. Case fatality rates associated with AB infections may approach 70% when infections are due to antimicrobial-resistant strains (1).
Acinetobacter can cause community-acquired bronchiolitis and tracheobronchitis in healthy children and tracheobronchitis in immunocompromised adults. Acinetobacter easily colonize tracheostomy sites. Hospital-acquired Acinetobacter pneumonias are frequently multilobar and complicated. Secondary bacteremia and septic shock are associated with a poor prognosis.
Acinetobacter species can also cause wound infections and 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 Acinetobacter 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 |
|---|---|
Hospital-acquired | Fecal colonization with Acinetobacter Indwelling devices Intensive care unit stay Length of hospital stay Previous infection Surgery Treatment with broad-spectrum antibiotics Wounds |
Community-acquired | Chronic lung disease Residence in a tropical climate, particularly after a natural disaster |
Multidrug-resistant | Exposure to patients who are colonized or infected Invasive procedures Mechanical ventilation, particularly if prolonged Prolonged hospitalization (particularly in the intensive care unit) Receipt of blood products Use of broad-spectrum antibiotics (eg, third-generation cephalosporins, carbapenems, fluoroquinolones) |
Drug resistance in Acinetobacter
Multidrug-resistant A. baumannii (MDR-AB) and, more specifically, carbapenem-resistant AB (CRAB) species have emerged, particularly in intensive care units (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 professionals, contaminated common equipment, and contaminated parenteral nutrition solutions.
Historically, Acinetobacter infections were associated with wars in Vietnam and Korea but more recently have been associated with wars in Iraq and Afghanistan, a large percentage of which involved antibiotic-resistant strains.
Diseases caused by Acinetobacter reference
1. Wong D, Nielsen TB, Bonomo RA, et al. Clinical and pathophysiological overview of Acinetobacter infections: A century of challenges. Clin Microbiol Rev. 2017;30(1):409–447. doi:10.1128/CMR.00058-16
Treatment of Acinetobacter Infections
Antibiotic therapy based on susceptibility testing
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 hygiene alone. Patients with more extensive infections should be treated with antibiotics and with debridement if necessary.
Mild infections with non-MDR pathogens typically respond to monotherapy.
Moderate to severe A. baumannii (AB) infections with non-MDR pathogens are usually treated with combination therapy until clinical response is seen. A typical combination includes a carbapenem (imipenem or meropenem) or ampicillin/sulbactam plus a fluoroquinolone or an aminoglycoside. Additional combinations may need to be considered depending on antibiotic susceptibilities.
AB has long had intrinsic resistance to many antimicrobials; therefore, empiric therapy should be informed by the likelihood of resistance, including local antibiograms. MDR-AB are defined as strains that are resistant to ≥1).
Severe CRAB infections are still typically treated with ampicillin/sulbactam along with an additional antimicrobial (2). Sulbactam/durlobactam is an alternative.
To prevent spread, health care professionals should use contact precautions (hand washing, barrier precautions) and appropriate ventilator care and cleaning for patients colonized or infected with MDR-AB.
Treatment references
1. Abdul-Mutakabbir JC, Griffith NC, Shields RK, Tverdek FP, Escobar ZK. Contemporary Perspective on the Treatment of Acinetobacter baumannii Infections: Insights from the Society of Infectious Diseases Pharmacists. Infect Dis Ther. 2021 Dec;10(4):2177-2202. doi:10.1007/s40121-021-00541-4
2. Tamma PD, Aitken SL, Bonomo RA, Mathers AJ, van Duin D, Clancy CJ. Infectious Diseases Society of America 2023 Guidance on the Treatment of Antimicrobial Resistant Gram-Negative Infections. Clin Infect Dis. Published online July 18, 2023. doi:10.1093/cid/ciad428
Key Points
A. baumannii (AB) accounts for about 80% of Acinetobacter infections and tends to occur in patients who are critically ill and hospitalized.
The most common site for infection is the respiratory system, but Acinetobacter species can also cause suppurative infections in any organ system.
Multidrug-resistant AB has become a problem; multidrug treatment chosen based on susceptibility testing may be necessary.
