article · Antimicrobial Agents and Chemotherapy
Researchers identified plasmid-mediated tet(X7), which confers high-level resistance to tigecycline, in five mcr-1.1-positive Escherichia coli isolates obtained from chickens in Egypt. The analysed isolates belonged to sequence types ST10 and ST155. In addition to tigecycline and colistin resistance elements, two IncFII plasmids of approximately 79 kilobases carrying the fosfomycin resistance gene fosA4 were detected. In all five isolates, the transposase ISCR3 belonging to the IS91 family was found adjacent to tet(X7), suggesting that it plays a functional role in mobilising this resistance gene. Furthermore, the findings represent the first reported detection worldwide of ST4-IncHI2 plasmids simultaneously carrying both tet(X7) and mcr-1.1 in poultry isolates.
Tigecycline and colistin serve as critical last-resort antibiotics for treating severe bacterial infections. The identification of poultry-associated bacteria carrying transferable plasmids with resistance to both therapies, as well as fosfomycin, raises serious public health concerns. Tracking how mobile elements facilitate the transfer of multiple drug resistance mechanisms is vital for understanding and controlling the dissemination of difficult-to-treat pathogens across food production systems.
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The plasmid-mediated <i>tet</i>(X7) conferring high-level tigecycline resistance was identified in five <i>mcr-1.1</i>-positive <i>Escherichia coli</i> strains (ST10 [<i>n</i> = 3] and ST155 [<i>n</i> = 2]) isolated from chickens in Egypt. Two fosfomycin-resistant <i>fosA4</i>-carrying IncFII plasmids (∼79 kb in size) were detected. Transposase IS<i>CR3</i> (IS<i>91</i> family) is syntenic with <i>tet</i>(X7) in all isolates, suggesting its role in the mobilization of <i>tet</i>(X7). To our knowledge, this is the first global report of ST4-IncHI2 plasmids cocarrying <i>tet</i>(X7) and <i>mcr-1.1</i> from chickens.
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DOI: 10.1128/aac.02084-20
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