In vivo activity of cefquinome against Escherichia coli in the thighs of neutropenic mice.

Cefquinome is a cephalosporin with broad-spectrum antibacterial activity, including activity against enteric Gram-negative bacilli such as Escherichia coli. We utilized a neutropenic mouse model of colibacillosis to examine the pharmacodynamic (PD) characteristics of cefquinome, as measured by organism number in homogenized thigh cultures after 24 h of therapy. Serum drug levels following 4-fold-escalating single doses of cefquinome were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The pharmacokinetic (PK) properties of cefquinome were linear over a dose range of 10 to 640 mg/kg of body weight. Serum half-lives ranged from 0.29 to 0.32 h. Dose fractionation studies over a 24-h dose range of 2.5 to 320 mg/kg were conducted every 3, 6, 12, or 24 h. Nonlinear regression analysis was used to determine which pharmacodynamic parameter best correlated with efficacy. The free percentage of the dosing interval that the serum levels exceed the MIC (fT>MIC) was the PK-PD index that best correlated with efficacy (R(2) = 73% for E. coli, compared with 13% for the maximum concentration of the free drug in serum [fCmax]/MIC and 45% for the free-drug area under the concentration-time curve from 0 to 24 h [fAUC0-24]/MIC). Subsequently, we employed a similar dosing strategy by using 4-fold-increasing total cefquinome doses administered every 4 h to treat animals infected with four additional E. coli isolates. A sigmoid maximum-effect (Emax) model was used to estimate the magnitudes of the %fT>MIC associated with net bacterial stasis, a 1-log10 CFU reduction from baseline, and a 2-log10 CFU reduction from baseline; the corresponding values were 28.01% ± 2.27%, 37.23% ± 4.05%, and 51.69% ± 9.72%. The potent bactericidal activity makes cefquinome an attractive option for the treatment of infections caused by E. coli.

Characterization of extended-spectrum ß-lactamase genes found among Escherichia coli isolates from duck and environmental samples obtained on a duck farm.

In this study, we focused on evaluating the occurrence of extended-spectrum ß-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.

Determination of residual clopidol in chicken muscle by capillary gas chromatography/mass spectrometry.

Clopidol was extracted from chicken with acetonitrile, and the extract was evaporated to about 5 mL. The concentrated solution was centrifuged and applied to a glass column filled with basic alumina. The column was eluted with methanol and the methanol was evaporated to dryness. The residue was derivatized with Sylon BFT and analyzed by gas chromatography/mass spectrometry (GC/MS). Mass characteristics of trimethylsilyl derivative of clopidol were interpreted manually. The selected-ion monitoring mode was performed at m/z 191, 248, 263, and 265. A sensitive, reproducible GC/MS method was developed for monitoring residues of clopidol in chickens. All recoveries of the drug from chicken muscle fortified at 1, 10, and 100 ng/g were > 65%, and relative standard deviations were < 15%. The detection limit was about 0.5 ng/g, and the quantitation limit was the lower limit of the standard curve, which was about 1 ng/g.