Identification and Characterization of a Novel SXT/R391 Integrative and Conjugative Element in a Proteus mirabilis Food Isolate.

Proteus mirabilis is an opportunistic human pathogen. In this study, a novel SXT/R391 integrative and conjugative element (ICE), named ICEPmiChnS012, was identified in the multidrug-resistant P. mirabilis strain S012 that was isolated from retail chicken in China. Whole genome sequencing revealed that ICEPmiChnS012 carried 22 resistance genes including aac(6')-Ib-cr, fosA3, blaOXA-1, blaCTX-M-65, and blaHMS-1. ICEPmiChnS012 harbored 10 copies of IS26 and IS26-mediated genetic new rearrangements caused variations in HS4 region. To our knowledge, an unusual gene cassette array dfrA1-ereA1-aadA2 was found in P. mirabilis in this study for the first time. And this is the first report of identification of aph3-VI and blaHMS-1 in VRIII region in P. mirabilis. The conjugation experiments proved that ICEPmiChnS012 could be transferred to Escherichia coli EC600 through conjugation. These findings demonstrated that ICEPmiChnS012 was a special ICE that carried the largest number of antimicrobial resistance genes in the family of SXT/R391 ICEs. This element could serve as an important vehicle for the dissemination of antibiotic resistance genes and should receive great concern.