Acinetobacter baumannii
One-Sentence Definition
Acinetobacter baumannii is a non-fermenting Gram-negative coccobacillus that persists in the hospital environment and causes ventilator-associated pneumonia, bloodstream infection, and wound infection with extreme drug resistance.
Taxonomy & Morphology
- Gram-negative coccobacillus, strictly aerobic, oxidase-negative, non-fermenting
- Often appears as pairs; can be mistaken for Neisseria on smear
- Grows on MacConkey as a non-lactose fermenter
Why it survives in hospitals
- Exceptional desiccation tolerance — survives weeks on dry surfaces
- Resistant to many disinfectants; strong Biofilm formation on plastic
- Colonizes ventilators, catheters, bedrails, and the hands of staff
- Highly efficient at acquiring resistance by Horizontal Gene Transfer — naturally competent for transformation
Clinical Syndromes
- Ventilator-associated pneumonia — the dominant presentation
- Bloodstream infection (CLABSI), wound and burn infection, occasionally meningitis after neurosurgery
- Combat and disaster-related wound infections
- Distinguishing colonization from infection in respiratory specimens is genuinely difficult
Diagnosis
- Culture and MALDI-TOF identification (Proteomics and MALDI Bioinformatics)
- Species-level resolution within the A. calcoaceticus–baumannii complex may need molecular or Whole-Genome Sequencing methods
Treatment & AMR
- Carbapenem resistance is now the norm in many regions, usually via OXA-23 and related class D carbapenemases, often with insertion sequences driving overexpression
- Additional layers: Efflux Pumps, porin loss, aminoglycoside-modifying enzymes
- Remaining options: sulbactam-durlobactam, cefiderocol, polymyxins, sometimes tigecycline or combinations — several are last-line with real toxicity
- Pan-drug-resistant isolates are reported
Public Health
- The A in ESKAPE Pathogens; a WHO critical-priority pathogen
- Outbreaks are typically environmental plus clonal; genomic typing separates the two (MLST and cgMLST, Plasmid and Mobile Element Analysis)
- Control depends on environmental cleaning and contact precautions (Infection Prevention and Control)
Research Relevance
- Target of AI-driven discovery: abaucin was identified by a deep-learning screen specifically against this organism — see AI for Antibiotic Discovery
Related MOCs
Active Recall Questions
- Which two environmental properties make this organism a hospital problem?
- Which enzyme family most commonly drives its carbapenem resistance?
- Why is interpreting a respiratory isolate difficult?