title: Characterization of extended-spectrum β-lactamase genes found among Escherichia coli isolates from duck and environmental samples obtained on a duck farm.
abstract: In this study, we focused on evaluating the occurrence of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli in fecal samples of healthy ducks and environmental samples from a duck farm in South China. Duck cloacal swabs and pond water samples were cultivated on MacConkey agar plates supplemented with ceftiofur. Individual colonies were examined for ESBL production. Bacteria identified as E. coli were screened for the presence of ESBL and plasmid-borne AmpC genes. The genetic relatedness, plasmid replicon type, and genetic background were determined. Of 245 samples analyzed, 123 had E. coli isolates with ceftiofur MICs higher than 8 μg/ml (116 [50.4%] from 230 duck samples and 7 [46.7%] from 15 water samples). bla(CTX-M), bla(SHV-12), bla(CMY-2), and bla(DHA-1) were identified in 108, 5, 9, and 1 isolates, respectively. The most common bla(CTX-M) genes were bla(CTX-M-27) (n = 34), bla(CTX-M-55) (n = 27), bla(CTX-M-24e) (n = 22), and bla(CTX-M-105) (n = 20), followed by bla(CTX-M-14a), bla(CTX-M-14b), bla(CTX-M-24a), and bla(CTX-M-24b). Although most of the CTX-M producers had distinct pulsotypes, clonal transmission between duck and water isolates was observed. bla(CTX-M) genes were carried by transferable IncN, IncF, and untypeable plasmids. The novel CTX-M gene bla(CTX-M-105) was flanked by two hypothetical protein sequences, partial ISEcp1 upstream and truncated IS903D, iroN, orf1, and a Tn1721-like element downstream. It is suggested that the horizontal transfer of bla(CTX-M) genes mediated by mobile elements and the clonal spread of CTX-M-producing E. coli isolates contributed to the dissemination of bla(CTX-M) in the duck farm. Our findings highlight the importance of ducks for the dissemination of transferable antibiotic resistance genes into the environment.
authors.affiliation: College of Veterinary Medicine, National Reference Laboratory of Veterinary Drug Residues (SCAU), South China Agricultural University, Guangzhou, China.
authors.forename: Junying
authors.initials: J
authors.lastname: Ma
authors.forename: Jian-Hua
authors.initials: JH
authors.lastname: Liu
authors.forename: Luchao
authors.initials: L
authors.lastname: Lv
authors.forename: Zhiyong
authors.initials: Z
authors.lastname: Zong
authors.forename: Yan
authors.initials: Y
authors.lastname: Sun
authors.forename: Hongqing
authors.initials: H
authors.lastname: Zheng
authors.forename: ZhangLiu
authors.initials: Z
authors.lastname: Chen
authors.forename: Zhen-Ling
authors.initials: ZL
authors.lastname: Zeng
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002681:China; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004372:Ducks / Q000382:microbiology*; D004783:Environmental Microbiology; D004926:Escherichia coli / Q000145:classification / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification*; D005243:Feces / Q000382:microbiology*; D005798:Genes, Bacterial; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D058889:Molecular Typing; D010957:Plasmids; D017422:Sequence Analysis, DNA; D018440:beta-Lactam Resistance; D001618:beta-Lactamases / Q000235:genetics / Q000378:metabolism*; D047090:beta-Lactams / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D047090:beta-Lactams; D001618:beta-Lactamases