Colistin-Resistant Acinetobacter baumannii: Beyond Carbapenem Resistance.

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Colistin-Resistant Acinetobacter baumannii: Beyond Carbapenem Resistance.

Clin Infect Dis. 2015 Jan 28;

Authors: Qureshi ZA, Hittle LE, O'Hara JA, Rivera JI, Syed A, Shields RK, Pasculle AW, Ernst RK, Doi Y

BACKGROUND:  With an increase in the use of colistin methansulfonate (CMS) to treat carbapenem-resistant A. 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 mechanism of colistin resistance, lipid A was subjected to matrix-assisted laser desorption 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 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 2, 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.

PMID: 25632010 [PubMed - as supplied by publisher]

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