Colistin-Resistant Acinetobacter baumannii: Beyond Carbapenem Resistance

• Published in: Clinical infectious diseases 2015-05, Vol.60 (9), p.1295-1303
• Main Authors: Qureshi, Zubair A., Hittle, Lauren E., O'Hara, Jessica A., Rivera, Jesabel I., Syed, Alveena, Shields, Ryan K., Pasculle, Anthony W., Ernst, Robert K., Doi, Yohei
• Format: Article
• Language: English
• Subjects: Acinetobacter baumannii - drug effects; Acinetobacter baumannii - genetics; Acinetobacter baumannii - isolation & purification; Acinetobacter baumannii - pathogenicity; Acinetobacter Infections - complications; Acinetobacter Infections - drug therapy; Acinetobacter Infections - microbiology; Acinetobacter Infections - mortality; Adult; Aged; Aged, 80 and over; Ampicillin - therapeutic use; and Commentaries; ARTICLES AND COMMENTARIES; Bacterial infections; Carbapenems - pharmacology; Carbapenems - therapeutic use; Colistin - pharmacology; Colistin - therapeutic use; CRE bacteria; Drug resistance; Drug Resistance, Multiple, Bacterial; Drug use; Electronic Health Records; Electrophoresis, Gel, Pulsed-Field; Ethanolamines - chemistry; Female; Gram-negative bacteria; Humans; Lipid A - chemistry; Lipids; Male; Mass spectrometry; Microbial Sensitivity Tests; Middle Aged; Multilocus Sequence Typing; Pneumonia, Ventilator-Associated - drug therapy; Pneumonia, Ventilator-Associated - microbiology; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Sulbactam - therapeutic use
• ISSN: 1058-4838; 1537-6591
• DOI: 10.1093/cid/civ048

Background. With an increase in the use of colistin methansulfonate (CMS) to treat carbapenem-resistant Acinetobacter baumannii infections, colistin resistance is emerging. Methods. Patients with infection or colonization due to colistin-resistant A. baumannii were identified at a hospital system in Pennsylvania. Clinical data were collected from electronic medical records. Susceptibility testing, pulsed-field gel electrophoresis (PFGE), and multilocus sequence typing (MLST) were performed. To investigate the mechanism of colistin resistance, lipid A was subjected to matrix-assisted laser desorption/ionization mass spectrometry. Results. Twenty patients with colistin-resistant A. baumannii were identified. Ventilator-associated pneumonia was the most common type of infection. Nineteen patients had received intravenous and/or inhaled CMS for treatment of carbapenem-resistant, colistin-susceptible A. baumannii infection prior to identification of colistin-resistant isolates. The 30-day all-cause mortality rate was 30%. The treatment regimen for colistin-resistant A. baumannii infection associated with the lowest mortality rate was a combination of CMS, a carbapenem, and ampicillin-sulbactam. The colistin-susceptible and -resistant isolates from the same patients were highly related by PFGE, but isolates from different patients were not, suggesting evolution of resistance during CMS therapy. By MLST, all isolates belonged to the international clone II, the lineage that is epidemic worldwide. Phosphoethanolamine modification of lipid A was present in all colistin-resistant A. baumannii isolates. Conclusions. Colistin-resistant A. baumannii occurred almost exclusively among patients who had received CMS for treatment of carbapenem-resistant, colistin-susceptible A. baumannii infection. Lipid A modification by the addition of phosphoethanolamine accounted for colistin resistance. Susceptibility testing for colistin should be considered for A. baumannii identified from CMS-experienced patients.