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 IS Ecp1 upstream and truncated IS 903D , iroN , orf1 , and a Tn 1721 -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.

This study investigated the prevalence of 16S rRNA methylase genes in 267 Enterobacteriaceae isolates collected from pets. The rmtB gene was detected in 69 isolates, most of which were clonally unrelated. The coexistence of the rmtB gene with the bla(CTX-M-9) group genes and/or qepA within the same IncFII replicons was commonly detected. The two dominant types of IncF plasmids, F2:A-:B-, carrying rmtB-qepA, and F33:A-:B-, carrying the rmtB-bla(CTX-M-9) group genes (and especially bla(CTX-M-65)), shared restriction patterns within each incompatibility group.

ABSTRACT OqxAB has recently been identified as one of the mechanisms of plasmid-mediated quinolone resistance (PMQR). Compared to what is observed for other PMQR determinants, there is a paucity of data with regard to the prevalence and epidemiology of OqxAB and its contribution to resistance to different antimicrobials. In this study, the prevalence and dissemination of oqxAB and other PMQR genes in Escherichia coli isolates from animals, farmworkers, and the environment in 2002 in China were investigated. Of the 172 E. coli isolates, 39.0% carried oqxA , while only 4.1%, 2.9%, and 0.6% carried qnr (1 qnrB6 isolate, 5 qnrS1 isolates, and 1 qnrD isolate), qepA , and aac(6′)-Ib- cr , respectively. Among the 33 isolates from farmworkers, 10 (30.3%) were positive for oqxA . oqxAB was associated with IS 26 and was carried on the 43- to 115-kb IncF transferable plasmid. Transconjugants carrying oqxAB showed 4- to 16-fold increases in the MICs of quinolones, 16- to 64-fold increases in the MICs of quinoxalines, 8- to 32-fold increases in the MICs of chloramphenicol and trimethoprim-sulfamethoxazole, and 4- to 8-fold increases in the MICs of florfenicol compared to the levels for the recipient. The pulsed-field gel electrophoresis (PFGE) analysis showed that the high levels of prevalence and dissemination of oqxA B in E. coli in animal farms were primarily due to the transmission of plasmids carrying oqxAB , although clonal transmission between human and swine E. coli isolates was observed. It is concluded that oqxAB was widespread in animal farms in China, which may be due to the overuse of quinoxalines in animals. This study warrants the prudent use of quinoxalines in food animals.