eMedicine Specialties > Infectious Diseases > Bacterial Infections

Acinetobacter

Author: Burke A Cunha, MD, Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital
Contributor Information and Disclosures

Updated: Aug 1, 2008

Introduction

Background

Acinetobacter baumannii is a pleomorphic aerobic gram-negative bacillus (similar in appearance to Haemophilus influenzae on Gram stain) commonly isolated from the hospital environment and hospitalized patients. A baumannii is a water organism and preferentially colonizes aquatic environments. This organism is often cultured from hospitalized patients' sputum or respiratory secretions, wounds, and urine. In a hospital setting, Acinetobacter commonly colonizes irrigating solutions and intravenous solutions.

Acinetobacter species have low virulence but are capable of causing infection. Most Acinetobacter isolates recovered from hospitalized patients, particularly those recovered from respiratory secretions and urine, represent colonization rather than infection.

Acinetobacter infections are uncommon but, when they occur, usually involve organ systems that have a high fluid content (eg, respiratory tract, CSF, peritoneal fluid, urinary tract), manifesting as nosocomial pneumonia, infections associated with continuous ambulatory peritoneal dialysis (CAPD), or catheter-associated bacteruria. The presence of Acinetobacter isolates in respiratory secretions in intubated patients nearly always represents colonization. Acinetobacter pneumonias occur in outbreaks and are usually associated with colonized respiratory-support equipment or fluids. Nosocomial meningitis may occur in colonized neurosurgical patients with external ventricular drainage tubes.

A baumannii is a multiresistant aerobic gram-negative bacillus sensitive to relatively few antibiotics. Multidrug-resistant Acinetobacter is not a new or emerging phenomenon, but A baumannii has always been an organism inherently resistant to multiple antibiotics.

Pathophysiology

In the uncommon situations in which Acinetobacter causes actual infection, the pathological changes that occur depend on the organ system involved. The pathological changes, as observed in patients with pneumonia, are indistinguishable from those caused by other noncavitating aerobic gram-negative bacilli that cause nosocomial pneumonias. Similarly, Acinetobacter urinary tract infections are clinically indistinguishable from catheter-associated bacteremias caused by other aerobic gram-negative bacilli.

Frequency

International

Acinetobacter commonly colonizes patients in the intensive care setting. Acinetobacter colonization is particularly common in patients who are intubated and in those who have multiple intravenous lines or monitoring devices, surgical drains, or indwelling urinary catheters. Acinetobacter infections are uncommon and occur almost exclusively in hospitalized patients.

Mortality/Morbidity

  • Although Acinetobacter is primarily a colonizer in the hospital environment, it occasionally causes infection. Mortality and morbidity resulting from A baumannii infection relate to the underlying cardiopulmonary immune status of the host rather than the inherent virulence of the organism.
  • Mortality and morbidity rates in patients who are very ill with multisystem disease are increased because of their underlying illness rather than the superimposed infection with Acinetobacter.

Race

Acinetobacter infection has no known racial predilection.

Sex

Acinetobacter infection has no known sexual predilection.

Age

Acinetobacter infection has no known predilection for age.

Clinical

History

  • Prolonged hospitalization or antibiotic therapy predisposes to Acinetobacter colonization.
  • Patients with Acinetobacter pneumonias occurring in the context of an outbreak in the intensive care unit (ICU) generally have a history of preceding contact with respiratory support monitors or equipment.
  • Patients with Acinetobacter colonization often have a history of prolonged hospitalization or antimicrobial therapy (with antibiotics that have little or no activity against Acinetobacter).

Physical

  • Because colonization is the rule and infection is the exception, colonized patients have no associated physical findings.
  • Patients with Acinetobacter infection have signs and symptoms related to the organ system involved, ie, wound infection, episodic outbreaks of nosocomial pneumonia, CAPD-associated peritonitis, nosocomial meningitis, or catheter-associated bacteruria.
  • The following is summarized from an article by Go and Cunha (1999):1
    • Acinetobacter commonly colonizes skin, oropharynx secretions, respiratory secretions, and urine.
    • Acinetobacter uncommonly colonizes the gastrointestinal tract and is associated with nosocomial pneumonias (which usually occur as outbreaks), bacteremias, and wound infections.
    • Acinetobacter infection is rarely associated with meningitis, endocarditis (native valve infective endocarditis and prosthetic valve endocarditis), peritonitis, urinary tract infections, community-acquired pneumonia, and cholangitis.

Causes

  • Antimicrobial therapy using agents with little or no activity against Acinetobacter predisposes to Acinetobacter colonization.
  • Residency in an ICU, particularly in the presence of other patients who are colonized with Acinetobacter, predisposes to colonization.

More on Acinetobacter

Overview: Acinetobacter
Differential Diagnoses & Workup: Acinetobacter
Treatment & Medication: Acinetobacter
Follow-up: Acinetobacter
References
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References

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Further Reading

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Keywords

Acinetobacter baumannii, A baumannii, Acinetobacter lwoffi, A lwoffi, Acinetobacter infection, A baumannii infection , Acinetobacter baumannii infection , Acinetobacter pneumonia, Acinetobacter nosocomial pneumonia, Acinetobacter colonization, Acinetobacter meningitis, Acinetobacter urinary tract infection, Acinetobacter peritonitis, Acinetobacter bacteruria, Acinetobacter endocarditis, Acinetobacter cholangitis, Mima polymorpha, nosocomial pneumonia, continuous ambulatory peritoneal dialysis, CAPD, catheter-associated bacteruria, UTI, URTI

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Contributor Information and Disclosures

Author

Burke A Cunha, MD, Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital
Burke A Cunha, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

Medical Editor

Charles S Levy, MD, Associate Professor, Department of Medicine, Section of Infectious Disease, George Washington University School of Medicine
Charles S Levy, MD is a member of the following medical societies: American College of Physicians, Infectious Diseases Society of America, and Medical Society of the District of Columbia
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

Richard B Brown, MD, FACP, Chief, Division of Infectious Diseases, Baystate Medical Center; Professor, Department of Internal Medicine, Tufts University School of Medicine
Richard B Brown, MD, FACP is a member of the following medical societies: Alpha Omega Alpha, American College of Chest Physicians, American College of Physicians, American Medical Association, American Society for Microbiology, Infectious Diseases Society of America, and Massachusetts Medical Society
Disclosure: Nothing to disclose.

CME Editor

Eleftherios Mylonakis, MD, Clinical and Research Fellow, Department of Internal Medicine, Division of Infectious Diseases, Massachusetts General Hospital
Eleftherios Mylonakis, MD is a member of the following medical societies: American Association for the Advancement of Science, American College of Physicians, American Society for Microbiology, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

Chief Editor

Michael Stuart Bronze, MD, Professor, Stewart G Wolf Chair in Internal Medicine, Department of Medicine, University of Oklahoma Health Science Center
Michael Stuart Bronze, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Physician Executives, American College of Physicians, American College of Physicians-American Society of Internal Medicine, American Federation for Clinical Research, American Medical Association, American Society for Microbiology, Association of Professors of Medicine, Association of Program Directors in Internal Medicine, Infectious Diseases Society of America, Oklahoma State Medical Association, and Southern Society for Clinical Investigation
Disclosure: Nothing to disclose.

 
 
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