title: Rapid determination of colistin resistance in clinical strains of Acinetobacter baumannii by use of the micromax assay.
abstract: Colistin is an old antibiotic which has been used as a therapeutic option for carbapenem- and multidrug-resistant Gram-negative bacteria, like Acinetobacter baumannii. This pathogen produces life-threatening infections, mainly in patients admitted to intensive care units. Rapid detection of resistance to colistin may improve patient outcomes and prevent the spread of resistance. For this purpose, Micromax technology was evaluated in four isogenic A. baumannii strains with known mechanisms of resistance to colistin and in 66 isolates (50 susceptible and 16 resistant). Two parameters were determined, DNA fragmentation and cell wall damage. To assess DNA fragmentation, cells trapped in a microgel were incubated with a lysing solution to remove the cell wall, and the released nucleoids were visualized under fluorescence microscopy. Fragmented DNA was observed as spots that diffuse from the nucleoid. To assess cell wall integrity, cells were incubated with a lysis solution which removes only weakened cell walls, resulting in nucleoid release exclusively in affected cells. A dose-response relationship was demonstrated between colistin concentrations and the percentages of bacteria with DNA fragmentation and cell wall damage, antibiotic effects that were delayed and less frequent in resistant strains. Receiver operating characteristic (ROC) curves demonstrated that both DNA fragmentation and cell wall damage were excellent parameters for identifying resistant strains. Obtaining ≤11% of bacteria with cell wall damage after incubation with 0.5 μg/ml colistin identified resistant strains of A. baumannii with 100% sensitivity and 96% specificity. Results were obtained in 3 h 30 min. This is a simple, rapid, and accurate assay for detecting colistin resistance in A. baumannii, with strong potential value in critical clinical situations.
authors.affiliation: Unidad de Genética, INIBIC-Complejo Hospitalario Universitario A Coruña, A Coruña, Spain.
authors.forename: Maria
authors.initials: M
authors.lastname: Tamayo
authors.forename: Rebeca
authors.initials: R
authors.lastname: Santiso
authors.forename: Fátima
authors.initials: F
authors.lastname: Otero
authors.forename: Germán
authors.initials: G
authors.lastname: Bou
authors.forename: José Antonio
authors.initials: JA
authors.lastname: Lepe
authors.forename: Michael J
authors.initials: MJ
authors.lastname: McConnell
authors.forename: José Miguel
authors.initials: JM
authors.lastname: Cisneros
authors.forename: Jaime
authors.initials: J
authors.lastname: Gosálvez
authors.forename: José Luis
authors.initials: JL
authors.lastname: Fernández
mesh_terms: D000151:Acinetobacter Infections / Q000382:microbiology; D040981:Acinetobacter baumannii / Q000187:drug effects* / Q000302:isolation & purification; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001433:Bacteriolysis; D002473:Cell Wall / Q000187:drug effects; D002876:Chromosomes, Bacterial / Q000187:drug effects; D003091:Colistin / Q000494:pharmacology*; D004269:DNA, Bacterial / Q000187:drug effects; D024881:Drug Resistance, Bacterial; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D003091:Colistin