Identification of a Novel Plasmid Carrying <i>mcr-4.3</i> in an <i>Acinetobacter baumannii</i> Strain in China

Abstract

Here, we identified <i>mcr-4.3</i> in <i>Acinetobacter baumannii</i>, which had not been previously observed to carry an <i>mcr</i> gene. The <i>mcr-4.3</i>-harboring <i>A. baumannii</i> strain AB18PR065 was isolated from pig feces from a slaughterhouse in Guangdong Province of China. The <i>mcr-4.3</i>-carrying pAB18PR065 is 25,602 bp in size and could not be transferred in conjugation, transformation, and electroporation experiments, as we did not find any conjugation-related genes therein. pAB18PR065 harbors two copies of type II toxin-antitoxin systems, which are functional in plasmid stabilization and maintenance. pAB18PR065 shares similarity only with one recently identified plasmid, pAb-MCR4.3 (35,502 bp), from a clinical <i>A. baumannii</i> strain. It is likely that the emergence of pAb-MCR4.3 was due to the insertion of an 11,386-bp, IS<i>Aba19</i>-based, composite transposon into pAB18PR065. These data indicate that <i>mcr-4.3</i> was captured by an <i>A. baumannii</i>-original plasmid via horizontal gene transfer.