Colistin resistance superimposed to endemic carbapenem-resistant Klebsiella pneumoniae: a rapidly evolving problem in Italy, November 2013 to April 2014

Using a Galleria mellonella animal model, we compared the virulence of two sequence type 258 (ST258) KPC-producing Klebsiella pneumoniae strains, which were representative of the two clades of this clonal lineage, with that of isogenic colistin-resistant mgrB mutants. With both strains, the mgrB mutants did not exhibit modification in virulence. In the G. mellonella model, the clade 1 strain (capsular type cps-1 [wzi29, producing KPC-2]) was significantly more virulent than the clade 2 strain (capsular type cps-2 [wzi154, producing KPC-3])