Acinetobacter baumannii

Acinetobacter baumannii
MICROBIOLOGY
· Aerobic gram-neg coccobacilli or rods, often mistaken for Neisseria or Moraxella on Gram stain.
· Common in environment (water, soil) and hospital (catheters, lotions, ventilation equipment).
· Grows on standard agar media.
· A. baumannii is the major species of Acinetobacter. Others occasional human pathogens include A. calcoaceticus, A. lwoffi, A. junii, A. johnsonii and A. baylyi .
· A. baumannii is low grade pathogen affecting compromised hosts (immunosuppression, post-surgical, ventilator-associated pneumonia, burn wounds, ICU pts, device-associated infections and malnutrition).
CLINICAL
· Emerging as important global, pan-resistant GNB nosocomial pathogen.
· Clearly pathogenic when recovered from blood and normally sterile body sites.
· Risks: hospitalization, ICU, surgery, antibiotic exposure and catheters.
· May cause nosocomial epidemics from contaminated common sources, e.g., ventilation equipment, catheters, etc.
· Diagnosis by standard aerobic bacterial culture.
· Lab isolations often meaningless (representing colonization) unless from
o normally sterile site,
o found as a dominant pathogen and moderate or heavy growth from potentially contaminated sites,
o outbreak and/or
o good clinical correlation.
SITES OF INFECTION
· Usually a cause of nosocomial infections.
· Pneumonia: nosocomial, especially ventilator-associated.
· Septicemia: often catheter-associated, or consequence of HAP or VAP.
· Wounds: burns, war wounds acquired in Iraq, natural disasters--hurricanes/earthquakes.
· Rare: meningitis (post-neurosurgical), liver abscess, endocarditis, urinary tract infections, brain abscess.
· Community-acquired: reports from Iraqi war theater, one major report from New Zealand.
TREATMENT
Antibiotics (Clin Infect Dis 2010;51:79)
· Antibiotic selection guided by in vitro sensitivity tests--most active: imipenem, ampicillin/sulbactam, colistin, tigecycline and amikacin.
· Imipenem: 0.5-1gm IV q6h, meropenem 0.5-1 gm IV q 8h, doripenem 500 mg IV q 8h.
· Ampicillin/sulbactam: 3 gm ampicillin/1.5 gm sulbactam IV q 6h (sulbactam is the active component).
· Tigecycline: 100 mg IV, then 50 mg IV q 12 h.
· Intrathecal: Polymyxin E 50,000 units/d.
· Pan-resistant isolates: colistin5 mg/kg/d divided q12h IV +/- imipenem or ampicillin/sulbactam.
· Other agents with variable activities: aminoglycosides, cephalosporins, minocycline, rifampin.
· Inhalation: colistin 1-3 mil units q 8h (use immediately after reconstitution) or tobramycin 300 mg twice daily.