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Objectives To characterize a representative self-transmissible multidrug resistance plasmid pHN7A8 isolated from an Escherichia coli from a dog in China, classified as F33:A-:B- by replicon sequence typing and carrying the blaTEM-1b, blaCTX-M-65, fosA3 and rmtB genes conferring resistance to penicillins, cephalosporins, fosfomycin and aminoglycosides, respectively. Methods pHN7A8 was sequenced using a whole-genome shotgun approach and the sequence analysed by comparison with reference plasmids. Results pHN7A8 is a circular molecule of 76 878 bp. blaCTX-M-65, fosA3 and rmtB are found in known contexts, interspersed with different mobile elements including ISEcp1, IS1, Tn2, IS1294, IS903 and four copies of IS26. This multiresistance region has only a single nucleotide difference from that of pXZ, an F2:A-:B- plasmid isolated from poultry in China. The pHN7A8 backbone carries genes encoding addiction and partitioning systems that promote plasmid maintenance and has a similar organization to pXZ, as well as IncFII plasmids such as R100, pC15-1a/pEK516 and pHK23, isolated in Japan, Canada/the UK and China, respectively, but with varying levels of identity, suggesting recombination. Conclusions pHN7A8 is a chimera that may have resulted from the acquisition, by recombination in the plasmid backbone, of the multiresistance region found in pXZ. This region appears to have evolved from the resistance determinant R100 through the stepwise integration of multiple antimicrobial resistance determinants from different sources by the actions of mobile elements and recombination. The successful dissemination of this multidrug resistance plasmid presents further challenges for the prevention and treatment of Enterobacteriaceae infections. [ABSTRACT FROM PUBLISHER]

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.

Insertion sequence common region (ISCR) elements are insertion sequences that have similarities to the IS91 family in both structure and function. ISCR elements differ from the insertion sequences by that they lack terminal inverted repeats (IRs), do not generate directly repeated sequence on insertion and are thought to be transposed by a mechanism termed rolling-circle (RC) transposition. ISCR elements, as a novel gene-capturing system, can mobilize any piece of adjacent DNA sequences. This powerful gene mobilization mechanism provides antibiotic resistance genes with a highly mobile genetic vehicle to transfer between different species of bacteria. Nineteen members of the ISCR family have been discovered until now in many Gram-negative pathogens. The majority of these elements are found to be closely associated with antimicrobial resistance genes that are not necessary components of the host genome, suggesting that ISCR elements may be responsible for the rapid transmission of bacterial multi-drug resistance. This review described some important aspects of ISCR elements, including their structure characteristics, classification, mobilization mechanism, origins and evolutions.

A confirmative method to determine clopidol residues in chicken muscle by gas chromatography-mass spectrometry (GC-MS) was developed. The analyte was extracted with ace tonitrile, and then purified with an Alumina-B cartridge column. The drug was derived at 80 degrees 3 for 60 min with Sylon BFT, and more toluene was added and then applied to GC-MS. The mass spectral characteristics of trimethylsilyl derivative of clopidol were interpreted, and selected ion monitoring (SIM) mode was performed at m/z 212, 214, 248 and 263. The clopidol was qualitatively identified by the ratio of relative abundance of the selected ions and determined quantitatively by SIM mode at m/z 248. In the meantime, the matrix effect was evaluated. The range of linearity was 5.0 - 500 microg/L with the correlation coefficients better than 0.998, and the detection limit was 0.5 microg/kg (S/N = 3) for clopidol. The average recoveries from chicken muscle fortified at 5, 10 and 20 microg/kg were 77.0%, 84.5% and 89.4%, respectively, and the relative standard deviations (RSD) were less than 6.9%. The established method is simple, sensitive and reproducible for the identification and quantification of clopidol residues in chicken muscle tissue.

A credible method was developed for the simultaneous determination of eleven steroid hormone residues in animal muscle tissues and eggs based on ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The eleven steroid hormones were testosterone, methyltestosterone, trenbolone, boldenone, nandrolone, methandienone, stanozolol, progesterone, nadrolone propionate, testosterone propionate and nadrolone phenylpropionate. The samples were extracted with tert-butyl methyl ether at alkaline pH and then cleaned up by freezing-lipid filtration. All these drugs can be assayed in 10 min by UPLC-MS/MS using electrospray ionization in positive ion mode and multiple reaction monitoring mode. The limits of detection were 0.3 microg/kg for testosterone, methyltestosterone, boldenone, methandienone and stanozolol, and 0.4 microg/kg for trenbolone nandrolone, progesterone, testosterone propionate and nadrolone phenylpropionate. Overall recoveries of testosterone, methyltestosterone, boldenone, methandienone and stanozolol were 62.3% - 105% from pork, beef, mutton and chicken muscle tissues, and eggs fortified at the 1, 2 and 10 microg/kg levels, and the relative standard deviations (RSDs) were 0.5% - 15%. The recoveries of trenbolone nandrolone, progesterone, testosterone propionate and nadrolone phenylpropionate were higher than 50.0%, and the RSDs were lower than 16%. The matrix calibration curve for each drug was linear (r > 0.99) from 1 to 100 microg/L. The established method is simple, rapid, sensitive and specific, and is appropriate for the identification and quantification of anabolic androgenic steroids in animal muscle tissues and eggs.

By the method of high-performance liquid chromatography (HPLC), this paper studied the hydrolysis characteristics of enrofloxacin under conditions of different pH, light, and microorganism to assess its ecological risk. The results showed that no ciprofloxacin was found in the hydrolyzed products of enrofloxacin. Under the conditions of 50 degrees C and pH 1 - 10, the hydrolyzation rate of enrofloxacin was less than 10% within 5 days. The half-life of enrofloxacin was longer than one year at normal temperature and in dark, and buffer's pH had no significant effects on the hydrolysis of enrofloxacin. The degradation of enrofloxacin in natural water was strongly affected by light. Under outdoor natural light condition, enrofloxacin degraded quickly and was not examined after 3 days; while under indoor natural light condition, it degraded slowly, with the degradation rate being 48%, 72% and 65% after 31 days when its initial concentration in water was 0.05, 0.2 and 1.0 mg x L(-1), respectively. Enrofloxacin was very steady in dark, and microorganisms had no significant effects on its degradation. Owing its rapid degradation under outdoor natural light condition, enrofloxacin might have no direct harmfulness to aquatic ecosystem, but its potential ecological risk should not be neglected once entering into aquatic ecosystem, especially in bottom mud.