Genetic basis of antimicrobial resistance and clonal dynamics of carbapenem-resistant Acinetobacter baumannii sequence type 191 in a Korean hospital

•All CRAB isolates showed an extensively drug-resistant phenotype.•The mutations in the lpxA gene were responsible for colistin resistance.•CRAB ST191 was the main ST during the last 4 years in the study hospital.•New ST191 clones showing different pulsotypes emerged sequentially as epidemic clones.

This study investigated the genetic basis of antimicrobial resistance and the epidemiological characteristics of 125 carbapenem-resistant Acinetobacter baumannii (CRAB) isolates collected from 2011 to 2012 in a Korean hospital. All CRAB isolates showed an extensively drug-resistant phenotype, but were susceptible to tigecycline. The blaOXA − 23 and armA genes were mainly responsible for resistance to carbapenems and aminoglycosides, respectively. Four colistin-resistant CRAB isolates with different pulsotypes were identified. All four colistin-resistant isolates had a deletion at nucleotide 776 in lpxA, while one also had an insertion at nucleotide 732 in lpxA. All CRAB isolates belonged to three sequence types (STs): ST191 (n = 118), ST208 (n = 6), and ST436 (n = 1), but were classified into 33 arbitrary pulsotypes. Of the CRAB ST191 isolates, two main arbitrary pulsotypes 5 (n = 20) and 18 (n = 17) emerged sequentially, but were not clonally related to CRAB isolates collected from 2009 to 2010 in the same hospital. Furthermore, of the two main pulsotypes identified among CRAB ST191 isolates from 2009 to 2010, one was clonally related to sporadic CRAB ST191 isolates from 2011 to 2012, but the other was not related to any CRAB isolate from 2011 to 2012. In conclusion, this study shows the clonal dynamics of CRAB ST191 isolates in a Korean hospital during the last four years.