Plasmid-mediated tigecycline-resistant gene <i>tet</i> (X4) in <i>Escherichia coli</i> from food-producing animals, China, 2008–2018

Abstract

The recent emergence of plasmid-mediated tigecycline resistance genes, <i>tet</i>(X3) and <i>tet</i>(X4), in animals and humans in China would pose a foreseeable threat to public health. To illustrate this paradigm shift in tigecycline resistance, here, covering the period 2008-2018, we retrospectively analysed a national strain collection of <i>Escherichia coli</i> (n = 2254), obtained from chickens and pigs, in six representative provinces of China. The gene <i>tet</i>(X4) was identified in five pig isolates collected in 2016 and 2018 from the provinces of Sichuan (3/15, 2018), Henan (1/25, 2018) and Guangdong (1/28, 2016), but not in the isolates prior to 2016. None of the isolates was detected harbouring <i>tet</i>(X3). All <i>tet</i>(X4)-positive <i>E. coli</i> exhibited high levels of tigecycline resistance (MICs, 16-64 mg/L), and two were confirmed as colistin resistant, harbouring chromosome-borne <i>mcr-1</i> gene. The gene <i>tet</i>(X4) was detected on a plasmid in all five isolates, whereas a co-location of <i>tet</i>(X4) on the chromosome of one isolate was observed. Diverse host strains and novel plasmids related to the <i>tet</i>(X4) gene were observed. Our timely findings of the recent emergence of <i>tet</i>(X4) gene in food animal support the rapid surveillance and eradication of this gene before it is established.