Abstract
Many novel tigecycline-inactivating enzymes encoded by tet(X) variants from different bacteria were discovered since the plasmid-mediated tet(X3) and tet(X4) genes conferring high-level resistance to tigecycline in Enterobacterales and Acinetobacter were reported. However, there have been no comprehensive studies of the prevalence of different tet(X) variants in poultry farms. In this study, we collected 45 chicken fecal samples, isolated tet(X)-positive strains, and performed antimicrobial susceptibility testing, conjugation assay, whole-genome sequencing, and bioinformatics analysis. A total of 15 tet(X)-bearing strains were isolated from 13 samples. Species identification and tet(X) subtyping analysis found that the 15 strains belonged to eight different species and harbored four different tet(X) variants. Genomic investigation showed that transmission of tet(X) variants was associated with various mobile genetic elements, and tet(X4) was the most prevalent variant transferred by conjugative plasmids. Meanwhile, we characterized a plasmid co-harboring tet(X6) and blaOXA–58 in Acinetobacter baumannii. In summary, we demonstrated that different tet(X) variants were widely disseminated in the chicken farming environment and dominated by tet(X4). This finding expands the understanding of the prevalence of tet(X) among different animal sources, and it was advocated to reduce the usage of antibiotics to limit the emergence and transmission of novel tet(X) variants in the poultry industry.
Highlights
Tigecycline is a broad-spectrum antibiotic of glycylcyclines and is one of the last-resort antibiotics to treat serious infections caused by multidrug-resistant (MDR) Gram-negative bacteria (Sun et al, 2013)
Out of 45 chicken fecal samples, a total of 15 tet(X)-positive strains were isolated from 13 samples (13/45, 28.89%)
These tet(X)-positive strains consisted of eight different species including five Citrobacter portucalensis, four E. coli, one Enterobacter hormaechei, one Citrobacter werkmanii, one Acinetobacter variabilis, one Acinetobacter lwoffii, one A. baumannii, and one Providencia alcalifaciens
Summary
Tigecycline is a broad-spectrum antibiotic of glycylcyclines and is one of the last-resort antibiotics to treat serious infections caused by multidrug-resistant (MDR) Gram-negative bacteria (Sun et al, 2013). A variety of tet(X) variants containing tet(X3.2) (Li et al, 2019), tet(X5) (Wang et al, 2019), tet(X6) (He et al, 2020; Liu et al, 2020; Peng et al, 2020), and tet(X14) (Cheng et al, 2020) have been detected in Empedobacter, Enterobacterales, and Acinetobacter so far. These widespread tet(X) variants will limit treatment options for MDR bacteria infections. We focused on the prevalence of tet(X) variants in cultivable bacteria among chicken fecal microbiota and demonstrated that tet(X) genes in diverse bacteria are worthy of continuous surveillance among different sources
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