Identification of a novel Acinetobacter baumannii clone in a US hospital outbreak by multilocus polymerase chain reaction/electrospray-ionization mass spectrometry

We investigated the relatedness of multidrug-resistant Acinetobacter baumannii isolates from a burn intensive care unit (BICU) outbreak, control isolates, and isolates from a previous 2007 outbreak by 3 molecular typing methods (repetitive sequence-based polymerase chain reaction [rep-PCR], broad-range PCR and electrospray ionization mass spectrometry [PCR/ESI-MS], and pulsed-field gel electrophoresis [PFGE]). Partial rpoB gene sequencing confirmed all tested isolates as A. baumannii. Molecular typing analysis showed that 17 of 19 outbreak isolates were indistinguishable or closely related to each other. Three of 4 non-BICU outbreak control isolates and 5 of 6 isolates from the previous outbreak closely matched the BICU outbreak genotype. The outbreak strain represented a novel strain type, ST96, on PCR/ESI-MS with a new combination of alleles not previously seen in the United States. The ST96 strain also represented a novel rpoB Seqtype. Results of PCR/ESI-MS and PFGE genotyping were most closely correlated, while rep-PCR and PCR/ESI-MS systems generated rapid results.