Genotyping of Acinetobacter baumannii strains isolated at a Japanese hospital over five years using targeted next-generation sequencing

Acinetobacter baumannii is a Gram-negative bacterial agent involved in nosocomial infections. In this five-year retrospective study, phylogenetic relationships among carbapenem-resistant A. baumannii strains that were isolated at Teikyo University Hospital in Tokyo metropolis, Japan, were explored. A panel of 72 carbapenem-resistant A. baumannii strains that isolated from January 2006 until August 2010 was studied. Next-Generation sequencing (NGS) was employed to perform large-scale genotyping of these isolates. They were separated, according to the time of isolation, into two genetically distinct groups, one correspondent to strains of the outbreak reported to local public health department in 2010 and the other contained strains from earlier isolations, suggesting different origins of the isolates. Moreover, taxa in each group showed two main clustering patterns. Multilocus sequence typing (MLST) study on 8 isolates from the last outbreak showed that they were from one sequence type, 92, displaying less discriminatory power comparing to large-sequence typing. The clonal lineage profiles produced in this retrospective study will be used as a reference database to compare future isolations of A. baumannii. This study demonstrates the power of NGS in conducting epidemiological researches, allowing a high resolution genotyping.