A distinct alleles and genetic recombination of pmrCAB operon in species of Acinetobacter baumannii complex isolates

• We determined complete sequences of pmrCAB operon for all isolates and evaluated nucleotide and amino acid polymorphisms.
• Each species of A. baumannii complex has divergent pmrCAB operon sequences, and we found a distinct pmrCAB allele allied with A. nosocomialis in gene trees.
• Different grouping in each gene tree suggests sporadic recombination or emergence of pmrCAB genes among Acinetobacter species.

To investigate pmrCAB sequence divergence in 5 species of Acinetobacter baumannii complex, a total of 80 isolates from a Korean hospital were explored. We evaluated nucleotide and amino acid polymorphisms of pmrCAB operon, and phylogenetic trees were constructed for each gene of prmCAB operon. Colistin and polymyxin B susceptibility was determined for all isolates, and multilocus sequence typing was also performed for A. baumannii isolates. Our results showed that each species of A. baumannii complex has divergent pmrCAB operon sequences. We identified a distinct pmrCAB allele allied with Acinetobacter nosocomialis in gene trees. Different grouping in each gene tree suggests sporadic recombination or emergence of pmrCAB genes among Acinetobacter species. Sequence polymorphisms among Acinetobacter species might not be associated with colistin resistance. We revealed that a distinct pmrCAB allele may be widespread across the continents such as North America and Asia and that sporadic genetic recombination or emergence of pmrCAB genes might occur.