International Spread of Tet(X4)-Producing Isolates.

Tigecycline resistance in bacteria has become a significant threat to food safety and public health, where the development of which is attributed to plasmid-mediated (X4) genes. In this study, the genomes of 613 (X4)-producing () isolates, available from public databases, are evaluated to determine their international prevalence and molecular characterization. These isolates have been disseminated in 12 countries across Asia and Europe. It was found that pigs and their products ( = 162) were the most common vehicle, followed by humans ( = 122), chickens ( = 60), and the environment ( = 49). Carbapenems-resistant genes (1.3%) and (0.2%) were identified, as well as colistin-resistant genes -1.1 (12.6%) and -3.1 (0.5%). It was noted that the tigecycline-resistant gene cluster C-D-J1 was identified in seven (1.1%) isolates. Phylogenomic results indicated that (X4)-producing isolates fell into seven lineages (lineages I, II, III, IV, V, VI, and VII), and international spread mainly occurred in Asian countries, especially China, Pakistan, Singapore, and Malaysia. Four forms of (X4) transposon units were found, including the I-type (IS(X4)-IS), II-type (ΔIS-(X4)-IS), III-type (IS(X4)-IS), and IV-type (IS(X4)-ΔIS). These findings underline further challenges for the spread of bearing (X4) gene.