Acinetobacter baumannii (Ab)

Classification

-gram-negative
-non-motile
-coccobacillus (pleomorphic)
-non-fastidious: don't require special conditions or substances for growth

Strict aerobe

How does it use oxygen?

How does it infect?

Opportunistically (wounds, underlying medical conditions, etc.); nosocomial infection

A. baumanni

Which strain is the most common cause of infection/greatest concern?

Some strains showing resistance to all commercially available antibiotics

Level of antibiotic resistance?

Opportunistic Infection

-occupies more tropical/warm environments
-can survive desiccation for weeks; fomites allow surface transmission
-higher rates of nosocomial infection in the summer than other seasons
-sometimes strains are found in soil and water-infect by colonizing skin, wounds, respiratory or GI tracts

Nosocomial or Community-Acquired?

-nosocomial infections more in developed countries via invasive healthcare tools (ex. ventilator, central line, catheter, surgery)
-community acquired infections more in Asia and Australia

Hospital Acquired Pneumonia

-infection usually caused by contaminated ventilators or respiratory care equipment, or intra-hospital transmission
-oral biofilms containing Ab may predispose an individual to respiratory infection upon intubation

Community Acquired Pneumonia

-Australia and Asia
-throat carriage
-severe and sudden onset; bacteremia
-high mortality rate, 40-60%

Common Ab Infections

-bloodstream infections
-meningitis
-battlefield trauma (wounded soldiers with infected burns or wounds)
-urinary tract infections
-endocarditis (it is very rare this is caused by Ab though)

Diagnosis

-requires cultures from patient specimen
-to test positive for infection one must have a positive culture AND clinical evidence of infection
-accurate and timely susceptibility profile is critical

Risk Factors

-recent surgery
-central line catheterization
-tracheostomy
- ventilators
-tubal feeding
-prior antibiotic use
-immunocompromised
-ICU stays, females, old age, pneumonia, diabetes, septic shock

Virulence Factors

-OmpA: allows binding to epithelial cells, complement resistance, biofilm transformation, and release of cytochrome C from mitochondria into cytosol (this induces apoptosis)
-Biofilms: resistance to complement, survival in hostile environments, can form on abiotic and biotic surfaces
-Capsule: resistance to complement-mediated killing and phagocytosis
-Pili: allows biofilm formation and initial attachment to cells; non-motile
-Phospholipase D: serum resistance
-Phospholipase C: host cell toxicity
-Antibiotic resistance