Various Profiles of Genes Addition to (X) in Isolates From Ducks in China.

To investigate tetracycline resistance and resistant genotype in , the tetracycline susceptibility of 212 isolates from China between 2011 and 2017 was tested. The results showed that 192 of 212 (90.6%) isolates exhibited resistance to tetracycline (the MICs ranged from 4 to 256 μg/ml). The results of PCR detection showed that, 170 of 212 (80.2%) isolates possessed the (X) gene. Other genes, including (A), (M), (Q), (O), (B), and (O/W/32/O), were found at frequencies of 20.8, 4.7, 1.4, 0.9, 0.9, and 0.5%, respectively. However, (C), (E), (G), (K), and (W) were not detected in any isolate. In these gene positive strains, 31 (14.6%), 2 (0.9%), 5 (2.4%), 1 (0.5%), 3 (1.4%) were detected containing (A)/(X), (M)/(O), (M)/(X), (O)/(X), and (Q)/(X) simultaneously, respectively. One isolates, R131, unexpectedly contained three genes, i.e., (M), (O), and (X). Sequence analysis of the gene ORFs cloned from isolates confirmed that (A), (B), (M), (O), (Q) and an unusual mosaic gene (O/W/32/O) were present in . The MIC results of ATCC 11845 transconjugants carrying (A), (B), (M), (O), (O/W/32/O), (Q), and (X) genes exhibited tetracycline resistance with MIC values ranging from 4 to 64 μg/ml. Additionally, the (X) gene could transfer into susceptible strain via natural transformation (transformation frequencies of ~10). In conclusion, the (A), (B), (M), (O), (O/W/32/O), (Q), and (X) genes were found and conferred tetracycline resistance in isolates. Moreover, the (X) is the main mechanism of tetracycline resistance in isolates. To our knowledge, this is the first report of (A), (B), (M), (O), (Q), and mosaic gene (O/W/32/O) in .