Last Updated on January 3, 2020 by Sagar Aryal
- The diagnosis of Acinetobacter infection is made by the growth of Acinetobacter from a patient specimen (eg, sputum, blood, cerebrospinal fluid) in the setting of other clinical findings that suggest an infection at that site.
- Since Acinetobacter colonization is common and treatment difficult and potentially associated with substantial toxicity, the distinction between colonization and infection, with treatment reserved for true infections, is important.
- As an example, Acinetobacter isolated from the sputum of a ventilated patient is more likely to represent colonization than infection in the absence of fever, leukocytosis, increased respiratory secretions, need for additional respiratory support, or a new abnormality on chest imaging.
- For cases of pneumonia, quantitative or semiquantitative cultures on sputum specimens may also be helpful in distinguishing between infection and colonization.
Specimens and Specimen Collection
A. baumannii has been isolated from blood, sputum, skin, pleural fluid, and urine, usually in device-associated infections.
- Collect blood by strict aseptic technique.
- Clean the rubber stopper of the blood culture bottle with an alcohol pad.
- Inoculate blood into blood culture bottles.
- Label the blood culture bottles with the date, name, and hospital number of the patient and send the specimens to the laboratory
- Keep inoculated bottles at 37oC or at room temperature.
- Give the patient a sterile wide-mouthed screw-capped container.
- Instruct the patient to inhale deeply 2–3 times and cough out deep from the chest.
- Open the container and spit the sputum into the bottle. Avoid saliva or nasal secretions.
- Close the container for further processing.
Bronchoalveolar Lavage (BAL) and Bronchial Washings
- Collect bronchial samples by injecting a variable volume of saline through a bronchoscope channel and aspirate in 3–4 aliquots.
- Collect the aspirate in sterile disposable red-capped 40 mL wide-mouthed container or sterile bottles.
- Collect bronchial washings by aspirating small amounts of instilled saline from the large airways of the respiratory tract.
- Store the samples in sterile disposable 40 mL wide-mouthed containers or if from ICU in sterile 100 mL bottles.
Perform Gram’s staining
Acinetobacter spp. appear Gram-negative and coccobacilli in shape.
Preliminary Identiﬁcation of Acinetobacter spp. by Culture Method and Propagation of Specimen Cultures
- Take samples from the collected tubes which showed Gram negative coccobacilli in the Gram stain.
- Streak samples with a sterile disposable inoculation loop on nutrient agar, MacConkey agar, or blood agar plates.
- Incubate the inoculated plates at 37oC under aerobic condition.
- Colony morphology on nutrient agar, blood agar, and MacConkey agar plates has to be observed and documented.
- On nutrient agar, non-mucoid, opaque, and circular colonies will be observed.
- On blood agar, nonhemolytic, opaque, circular, and gray color colonies will be observed.
- On MacConkey agar, non-lactose, fermenting, opaque, and circular colonies will be observed.
- Inoculate the biochemical reactions for preliminary identiﬁcation.
- Cytochrome oxidase test (Negative)
- Mannitol motility medium (Mannitol not fermented and Non-motile)
- Triple sugar iron agar ( Alkaline butt and slant; No H2S or gas)
- Indole test (Negative for indole)
- Citrate utilization test (Citrate positive)
- Urease test (Negative)
- Inoculate the biochemicals for species identiﬁcation.
- Oxidative-fermentative medium (Oxidative utilization of Glucose)
- Arginine decarboxylase test (Positive)
- Nitrate reduction test (Negative)
- Interpret the results based on positive and negative controls.
- Although carbapenems are effective antibiotics to treat A. baumannii infections, the rate of carbapenem-resistant A. baumannii isolates has been increasing gradually.
- Imipenem or ceftazidime combined with aminoglycosides is used for serious infections.
- Only a few effective antibiotic options are available to treat MDR A. baumannii infections. To combat MDR or pandrug-resistant (PDR) A. baumannii, which are resistant to all available antibiotics, combination therapies, including colistin/imipenem, colistin/meropenem, colistin/rifampicin, colistin/tigecycline, colistin/sulbactam, colistin/teicoplanin, and imipenem/sulbactam, have been extensively studied.
Prevention of Infection
- Acinetobacter can live on the skin and may survive in the environment for several days, which makes Acinetobacter baumannii prevention a delicate issue.
- Careful attention to infection control procedures, such as hand hygiene and environmental cleaning, can reduce the risk of transmission.
- Patients are placed in contact isolation if the pathogen was determined to be MDR.
Hand hygiene is the most fundamental, effective and cost-effective strategy for reducing cross-infection and avoiding the spread of resistant bacteria.
- The microbiology laboratory should notify clinicians in a timely and reliable way when an XDR-GNB strain is identified.
- Clinicians may implement contact precaution measures such as single room and partial separation of at least 1 m between beds for patients infected with XDR-GNB and to reduce the practice of sharing devices.
- Sphygmomanometer, stethoscope, thermometer, infusion pump and other relevant devices should be provided specifically for patients with XDR-GNB infection
In the ICU and other wards with highly prevalent XDR-GNB strains, patients should be screened with samples of perianal and rectal swabs for CRE, wound secretion and nasopharyngeal region for XDR non- fermenters to promptly identify resistant bacteria by way of conventional or rapid diagnostic methods. The patients should be isolated appropriately.
Environmental surface disinfection
- The surface of the objects frequently contacted by healthcare staff and patients in the hospital environment should be disinfected regularly and completely.
- Fluorescence labeling or the ATP Hygiene Monitoring System can be used to monitor the effectiveness of disinfection and thus ensure that the transmission of resistant strains is effectively blocked.
Patients colonized with XDR-GNB may have a whole-body sponge bath with chlorhexidine, which is helpful for reducing catheter-related bloodstream infections.
- Lee, C. R., Lee, J. H., Park, M., Park, K. S., Bae, I. K., Kim, Y. B., Lee, S. H. (2017). Biology of Acinetobacter baumannii: Pathogenesis, Antibiotic Resistance Mechanisms, and Prospective Treatment Options. Frontiers in cellular and infection microbiology, 7, 55. doi:10.3389/fcimb.2017.00055
- Asif, M., Alvi, I. A., & Rehman, S. U. (2018). Insight into Acinetobacter baumannii: pathogenesis, global resistance, mechanisms of resistance, treatment options, and alternative modalities. Infection and drug resistance, 11, 1249–1260. doi:10.2147/IDR.S166750