Acinetobacter


Article Author:
Mark Brady


Article Editor:
Najwa Pervin


Editors In Chief:
Kranthi Sitammagari
Mayank Singhal


Managing Editors:
Avais Raja
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Khalid Alsayouri
Trevor Nezwek
Radia Jamil
Patrick Le
Anoosh Zafar Gondal
Saad Nazir
William Gossman
Hassam Zulfiqar
Hussain Sajjad
Steve Bhimji
Muhammad Hashmi
John Shell
Matthew Varacallo
Heba Mahdy
Ahmad Malik
Sarosh Vaqar
Mark Pellegrini
James Hughes
Beata Beatty
Beenish Sohail
Nazia Sadiq
Hajira Basit
Phillip Hynes


Updated:
12/28/2018 11:30:28 AM

Introduction

Acinetobacter is a gram-negative, aerobic, non-fermentative, oxidase negative and nonmotile organism.Acinteobacter has several different species but A.baumanii has the greatest known clinical significance. Acinetobacter can be found in soil and water.In patients, they are frequently cultured from the urine, saliva, respiratory secretions and open wounds. The organism is also known to colonize intravenous fluids and other irrigation solutions.[1][2]

In general, Acinetobacter has low virulence but is capable of causing infection in immunocompromised and neutropenic patients. Most of the infections are a result of nosocomial spread and colonization rather than de novo infections. Thus, great care is required when acinetobacter is isolated - whether it is an actual infection or just colonization. Risk factors for Acinetobacter infection include:

  1. Prolonged stay in the intensive care until 
  2. Prior antibiotic exposure 
  3. Mechanical ventilation 
  4. Use of a central venous catheter
  5. Hemodialysis

Most acinetobacter infections are group outbreaks, and isolated cases are rare. Infections may complicate intravenous (IV) catheter treatment, mechanical ventilation and even peritoneal dialysis. In most cases, the presence of Acinetobacter in respiratory secretions of ventilated patients represents colonization.

Etiology

Even though Acinetobacter is mostly a nosocomial pathogen and is isolated from hospitalized patients, care should be exercised in determining if the isolate is a cause or simply a result of colonization. Acinetobacter is a water-loving organism and has the propensity to colonize body organs that contain fluid. Thus, in hospitalized patients, Acinetobacter is often found in the peritoneal fluid, cerebrospinal fluid (CSF), saliva, respiratory secretions and urinary tract.[3][4]

Epidemiology

Acinetobacter gained clinical significance in the 1960s with the increasing growth of Intensive care units at hospitals. [5]Though Acinetobacter is an organism of low virulence, its ability to survive dessication and persist in the environment for extended duration of time makes it easily transmissible in the healthcare setting. Nosocomial spread by healthcare personnel, respiratory equipment like ventilators and other devices has been reported frequently. It can be found in all types of secretions such as wounds, saliva, urine, and blood. The organism has low virulence but is still capable of causing infections in patients with febrile neutropenia and those who have received organ transplants.[6]

Acinetobacter has also been recognized in wounds sustained by combat injuries in returning soldiers from Iraq and Afghanistan.

Mortality/Morbidity

The morbidity of this organism is related to the patient's underlying medical condition and immune status. The organism is not very virulent but due to various innate mechanisms it has the capacity to acquire resistance. Multidrug-resistant , extensively drug resistant and pan-drug resistant isolates of Acinetobacter have been described as non-susceptible to at least one agent in three or more antibiotic classes, non-susceptible to at least one agent in all but two or fewer antibiotic classes and non-susceptible to all antibiotic classes. Multi-drug resistant Acinetobacter was designated a threat category of ‘Serious’ Center of disease Control Antimicrobial resistance report published in 2013. Though not virulent by itself, the morbidity and mortality of Acinetobacter are high in sick patients with multiorgan disease. In the case of infections being caused by resistant strains of A.baumanii, mortality rates of upto 70% have been reported. [5]

Pathophysiology

Various mechanisms contribute to the pathogenesis and virulence of Acinetobacter. Acinetobacter elaborate Lipopolysaccharide (LPS) or Lipooligosaccharide (LOS) in their outer membranes. Modification in the synthesis of these structures impart antibiotic resistance and increased resistance dessication. Acinetobacter species also have Capsules that protect them from complement mediated killing. Pili on the surface on Acinetobacter contribute to its twitching motility, biofilm formation and adherence to environmental surfaces. Acinetobacter also secrete various proteins that lead to antibiotic resistance by efflux or degradation. [7]

Histopathology

The infection caused by Acinetobacter is similar in histopathology as any other gram-negative bacilli. Gross or microscopic observation do not provide any clue to the organism and culture is required to confirm the diagnosis.

History and Physical

Prolonged hospitalization or antibiotic therapy predisposes to Acinetobacter colonization, and because colonization is the rule and infection is the exception, colonized patients have no physical findings.

Most patients are in hospital when infected with Acinetobacter. The one organ most commonly involved is the lung, primarily because of colonization of the airways and respiratory equipment used for mechanical ventilation.

Pneumonia, wound infection, catheter-associated bacteremia or nosocomial meningitis have all been described by Acinetobacter.

There are no pathognomic findings in Acinetobacter infections, and they need to be differentiated from other gram-negative infections like Enterobacter, Burkholderia, Pseudomonas, and Serratia. Since Acinetobacter is chiefly a colonizing organism, the physician has the onus to prove that it is causing the pathology in any given clinical scenario.

Evaluation

Acinetobacter is a common colonizer of patients in the intensive care unit and those who have multiple comorbid disorders. It is most likely to cause infections in patients who are immunocompromised and those with a compromise of their cardiopulmonary system. The organism can readily be cultured, but the findings need to be correlated to the clinical picture.

Laboratory Studies

There may be leucocytosis, with a left shift. However, the findings are nonspecific and do not always indicate the presence of a bacterial infection. When there is an outbreak of Acinetobacter, the organism is usually readily isolated and cultured from body fluids. More important, the outbreak usually involves multiple patients.

Imaging Studies

A chest x-ray is required if pneumonia is suspected. Other imaging tests depend on the signs and symptoms.

Procedures

If meningitis is suspected, then CSF needs to be analyzed and cultured.

Histologic Findings

There are no specific histopathological features of an Acinetobacter infection that can differentiate it from any other gram-negative bacilli

Treatment / Management

Being a gram-negative organism, the drugs used to treat Acinetobacter infections include the aminoglycosides, fourth-generation cephalosporins, tigecycline, and rifampin. The organism will not respond to macrolides, third-generation cephalosporins, and penicillin. When an infection is suspected in the presence of a long-term catheter or a pacemaker, it should be removed. [6][7][8][9]

Any external device, infected line, shunt or drain must be removed to obtain a cure. If the patient has a collection of an abscess or necrotic tissue, it needs to be debrided thoroughly.

One should avoid treating colonization as it only leads to more antibiotic resistance.

Over the last few years, drug resistance has become a common problem in the United States. Anti-microbials which may be used in Acinetobacter infections include colistin, carbapenems, tigecycline, polymyxin, amikacin, and beta-lactam/beta-lactamase combinations. But, there have been more recent outbreaks with extensively drug resistant Acinetobacter which makes the management of these infections much more complicated. The duration of therapy is from 7 to 10 days, depending on the patient illness.

Pearls and Other Issues

Patients in the intensive care unit are the most difficult to treat as colonization is common and it is difficult to distinguish this from an infection. All patients who are noted to have colonization with Acinetobacter should be isolated from other patients to prevent further colonization.Once an infection is treated, the patient's clinical course must be followed rather than cultures, because colonization may offer a falsely positive diagnosis.

The prognosis of an isolated Acinetobacter infection is excellent in patients who are otherwise healthy. Patients who are immunosuppressed tend to have a poor outcome.

Enhancing Healthcare Team Outcomes

Over the past decade, Acinetobacter infections have become common in hospitalized patients. Since this organism can infect almost any organ system a multidisciplinary approach to diagnosis and management is essential. Often the organism is difficult to isolate because of colonization and hence an infectious disease consult should be made. Infection control teams should be involved earlier on to prevent out-breaks and utilize ways to prevent nosocomial transmission by eradication of bacteria and strict isolation techniques. The outcomes for most patients with Acinetobacter infection is excellent as long as there is no other comorbidity. However, those with immunosuppression may have a guarded prognosis.

Management should involve a coordinated effort of nurses, pharmacists, and clinicians.


Interested in Participating?

We are looking for contributors to author, edit, and peer review our vast library of review articles and multiple choice questions. In as little as 2-3 hours you can make a significant contribution to your specialty. In return for a small amount of your time, you will receive free access to all content and you will be published as an author or editor in eBooks, apps, online CME/CE activities, and an online Learning Management System for students, teachers, and program directors that allows access to review materials in over 500 specialties.

Improve Content - Become an Author or Editor

This is an academic project designed to provide inexpensive peer-reviewed Apps, eBooks, and very soon an online CME/CE system to help students identify weaknesses and improve knowledge. We would like you to consider being an author or editor. Please click here to learn more. Thank you for you for your interest, the StatPearls Publishing Editorial Team.

Acinetobacter - Questions

Take a quiz of the questions on this article.

Take Quiz
Which of the following is not true in regards to an Acinetobacter infection?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
In hospital patients, which is not a common location to find an Acinetobacter infection?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A 65-year-old male is admitted to the intensive care unit after a traumatic injury. He is mechanically ventilated for respiratory failure. On the fourth day of admission, he becomes febrile, and the chest x-ray reveals an opacity in the left lower lobe suggestive of pneumonia. Tracheal aspirate cultures grow Acinetobacter baumannii. Susceptibilities are pending. The clinical team is involved and reports no other cases at present and no past cases with drug-resistant Acinetobacter baumannii. Which antimicrobial should be initiated in this patient?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up

Acinetobacter - References

References

Eze EC,Chenia HY,Zowalaty MEE, {i}Acinetobacter baumannii{/i} biofilms: effects of physicochemical factors, virulence, antibiotic resistance determinants, gene regulation, and future antimicrobial treatments. Infection and drug resistance. 2018     [PubMed]
Munier AL,Biard L,Legrand M,Rousseau C,Lafaurie M,Donay JL,Flicoteaux R,Mebazaa A,Mimoun M,Molina JM, Incidence, risk factors and outcome of multi-drug resistant Acinetobacter baumannii nosocomial infections during an outbreak in a burn unit. International journal of infectious diseases : IJID : official publication of the International Society for Infectious Diseases. 2018 Dec 6     [PubMed]
Garnacho-Montero J,Timsit JF, Managing Acinetobacter baumannii infections. Current opinion in infectious diseases. 2018 Dec 4     [PubMed]
Giacobbe DR,Mikulska M,Viscoli C, Recent advances in the pharmacological management of infections due to multidrug-resistant Gram-negative bacteria. Expert review of clinical pharmacology. 2018 Dec     [PubMed]
de Azevedo FKSF,Dutra V,Nakazato L,Mello CM,Pepato MA,de Sousa ATHI,Takahara DT,Hahn RC,Souto FJD, Molecular epidemiology of multidrug-resistant Acinetobacter baumannii infection in two hospitals in Central Brazil: the role of ST730 and ST162 in clinical outcomes. Journal of medical microbiology. 2018 Dec 5     [PubMed]
Wong D,Nielsen TB,Bonomo RA,Pantapalangkoor P,Luna B,Spellberg B, Clinical and Pathophysiological Overview of Acinetobacter Infections: a Century of Challenges. Clinical microbiology reviews. 2017 Jan;     [PubMed]
Weber BS,Harding CM,Feldman MF, Pathogenic Acinetobacter: from the Cell Surface to Infinity and Beyond. Journal of bacteriology. 2015 Dec 28;     [PubMed]

Disclaimer

The intent of StatPearls is to provide practice questions and explanations to assist you in identifying and resolving knowledge deficits. These questions and explanations are not intended to be a source of the knowledge base of all of medicine, nor is it intended to be a board or certification review of PA-Hospital Medicine. The authors or editors do not warrant the information is complete or accurate. The reader is encouraged to verify each answer and explanation in several references. All drug indications and dosages should be verified before administration.

StatPearls offers the most comprehensive database of free multiple-choice questions with explanations and short review chapters ever developed. This system helps physicians, medical students, dentists, nurses, pharmacists, and allied health professionals identify education deficits and learn new concepts. StatPearls is not a board or certification review system for PA-Hospital Medicine, it is a learning system that you can use to help improve your knowledge base of medicine for life-long learning. StatPearls will help you identify your weaknesses so that when you are ready to study for a board or certification exam in PA-Hospital Medicine, you will already be prepared.

Our content is updated continuously through a multi-step peer review process that will help you be prepared and review for a thorough knowledge of PA-Hospital Medicine. When it is time for the PA-Hospital Medicine board and certification exam, you will already be ready. Besides online study quizzes, we also publish our peer-reviewed content in eBooks and mobile Apps. We also offer inexpensive CME/CE, so our content can be used to attain education credits while you study PA-Hospital Medicine.