Identification of novel tetracycline resistance gene tet (X14) and its co-occurrence with tet (X2) in a tigecycline-resistant and colistin-resistant Empedobacter stercoris

Abstract

Tigecycline is one of the last-resort antibiotics to treat severe infections. Recently, tigecycline resistance has sporadically emerged with an increasing trend, and Tet(X) family represents a new resistance mechanism of tigecycline. In this study, a novel chromosome-encoded tigecycline resistance gene, tet(X14), was identified in a tigecycline-resistant and colistinresistant Empedobacter stercoris strain ES183 recovered from a pig fecal sample in China. Tet(X14) shows 67.14-96.39% sequence identity to the other variants [Tet(X) to Tet(X13)]. Overexpression of Tet(X14) in Escherichia coli confers 16fold increase in tigecycline MIC (from 0.125 to 2 mg/L), which is lower than that of Tet(X3), Tet(X4) and Tet(X6). Structural modelling predicted that Tet(X14) shared a high homology with the other 12 variants with RMSD value from 0.003 to 0.055, and Tet(X14) can interact with tetracyclines by a similar pattern as the other Tet(X)s. tet(X14) and two copies of tet(X2) were identified on a genome island with abnormal GC content carried by the chromosome of ES183, and no mobile genetic elements were found surrounding, suggesting that tet(X14) might be heterologously obtained by ES183 via recombination. Blasting in Genbank revealed that Tet(X14) was exclusively detected on the chromosome of Riemerella anatipestifer, mainly encoded on antimicrobial resistance islands. E. stercoris and R. anatipestifer belong to the family Flavobacteriaceae, suggesting that the members of Flavobacteriaceae maybe the major reservoir of tet(X14). Our study reports a novel chromosome-encoded tigecycline resistance gene tet(X14). The expanded members of Tet(X) family warrants the potential large-scale dissemination and the necessity of continuous surveillance for tet(X)-mediated tigecycline resistance.

Genetic Characterization of the Tetracycline-Resistance Gene tet(X) Carried by Two Epilithonimonas Strains Isolated from Farmed Diseased Rainbow Trout, Oncorhynchus mykiss in Chile

“…It must be noted that among all tet (X) genes reported in flavobacteriaceae strains from fish, only in this study, it was confirmed that the detected tet (X) genes conferred the tetracycline-resistance phenotype, considering that both Epilithonimonas strains showed an MIC of oxytetracycline of 128 µg/mL, which is within the expected level of resistance to oxytetracycline mediated by the Tet(X) activity. This value is in agreement with previous studies in which tet (X) genes heterologously expressed by E. coli transconjugants harboring recombinant plasmids exhibited MIC values of 128–256 µg/mL [ 12 , 40 , 51 , 52 ].…”

“…This misidentification is very relevant considering that F. psychrophilum species does not carry specific genes for resistance to tetracyclines, as occurs with pathogenic strains of fish and humans belonging to the Chryseobacterium clade, including several species belonging to the Chryseobacterium, Empedobacter, and Riemerella genus, among others, which have been reported to carry the tet (X) gene [ 38 , 39 , 40 , 41 , 42 ]. As a result of this, it has been hypothesized that the Flavobacteriaceae family could be a potential ancestral source of the tigecycline-resistance gene tet (X), as was recently claimed [ 43 ].…”

Molecular Characterization of Cronobacter sakazakii Strains Isolated from Powdered Milk

“…They can circulate without being detected, unless induced by colistin [ 73 , 74 , 75 ]. The presence of mobile genes that are resistant to colistin ( mcr ) is a worldwide concern because colistin is perceived as a last resort antimicrobial to treat infections caused by multi-resistant Enterobacteriaceae [ 76 ]. The bla CSA family of genes, resistant to class C β-lactamase, was described by Müller et al [ 77 ].…”

Acquisition and Spread of Antimicrobial Resistance: A tet(X) Case Study

“…The currently identified range of Tet X variants include Tet X–Tet X14, with a variable level of amino acid sequence identity, with the lowest similarity between Tet X and Tet X14 at 67% [ 29 ]. Presumably, this is a reflection of natural diversity of FMOs that have been acquired from different taxonomic entities and different ecological niches.…”