Pharmacokinetic/pharmacodynamic integration of amphenmulin: a novel pleuromutilin derivative against Mycoplasma gallisepticum.

Amphenmulin is a novel pleuromutilin derivative with great anti-mycoplasma potential. The present study evaluated the action characteristics of amphenmulin against Mycoplasma gallisepticum using pharmacokinetic/pharmacodynamic (PK/PD) modeling approaches. Following intravenous administration, amphenmulin exhibited an elimination half-life of 2.13 h and an apparent volume of distribution of 3.64 L/kg in healthy broiler chickens, demonstrating PK profiles of extensive distribution and rapid elimination. The minimum inhibitory concentration (MIC) of amphenmulin against M. gallisepticum was determined to be 0.0039 µg/mL using the broth microdilution method, and the analysis of the static time-kill curves through the sigmoid Emax model showed a highly correlated relationship (R ≥ 0.9649) between the kill rate and drug concentrations (1-64 MIC). A one-compartment open model with first-order elimination was implemented to simulate the in vivo anti-mycoplasma effect of amphenmulin, and it was found that bactericidal levels were reached with continuous administration for 3 days at doses exceeding 0.8 µg/mL. Furthermore, the area under the concentration-time curve divided by MIC (AUC/MIC) correlated well with the anti-mycoplasma effect of amphenmulin within 24 h after each administration, with a target value of 904.05 h for predicting a reduction of M. gallisepticum by 1 Log10CFU/mL. These investigations broadened the antibacterial spectrum of amphenmulin and revealed its characteristics of action against M. gallisepticum, providing a theoretical basis for further clinical development.IMPORTANCEMycoplasma has long been recognized as a significant pathogen causing global livestock production losses and public health concerns, and the use of antimicrobial agents is currently one of the mainstream strategies for its prevention and control. Amphenmulin is a promising candidate pleuromutilin derivative that was designed, synthesized, and screened by our laboratory in previous studies. Moreover, this study further confirms the excellent antibacterial activity of amphenmulin against Mycoplasma gallisepticum and reveals its action characteristics and model targets on M. gallisepticum by establishing an in vitro pharmacokinetic/pharmacodynamic synchronization model. These findings can further broaden the pharmacological theoretical basis of amphenmulin and serve as data support for its clinical development, which is of great significance for the discovery of new antimicrobial drugs and the control of bacterial diseases in humans and animals.

Rapid Dissemination of blaNDM-5 Gene among Carbapenem-Resistant Escherichia coli Isolates in a Yellow-Feather Broiler Farm via Multiple Plasmid Replicon.

Although carbapenems have not been approved for animal use, carbapenem-resistant Escherichia coli (CREC) strains are increasingly being detected in food-producing animals, posing a significant public health risk. However, the epidemiological characteristics of CREC isolates in yellow-feather broiler farms remain unclear. We comprehensively investigated the genetic features of carbapenem-resistance genes among E. coli isolates recovered from a yellow-feather broiler farm in Guangdong province, China. Among the 172 isolates, 88 (51.2%) were recovered from chicken feces (88.5%, 54/61), the farm environment (51.1%, 24/47), and specimens of dead chickens (15.6%, 41/64). All CREC isolates were positive for the blaNDM-5 gene and negative for other carbapenem-resistance genes. Among 40 randomly selected isolates subjected to whole-genome sequencing, 10 belonged to distinct sequence types (STs), with ST167 (n = 12) being the most prevalent across different sources, suggesting that the dissemination of blaNDM-5 was mainly due to horizontal and clonal transmission. Plasmid analysis indicated that IncX3, IncHI2, and IncR-X1-X3 hybrid plasmids were responsible for the rapid transmission of the blaNDM-5 gene, and the genetic surrounding of blaNDM-5 contained a common mobile element of the genetic fragment designated "IS5-△ISAba125-blaNDM-5-bleMBL-trpF-dsbC". These findings demonstrate a critical role of multiple plasmid replicons in the dissemination of blaNDM-5 and carbapenem resistance.

Elimination patterns of dimetridazole in egg of laying hens and tissues of broiler after oral administration.

Dimetridazole (DMZ) is a broad-spectrum anti-anaerobic and antiprotozoal drug extensively used for the control of blackhead disease in poultry (especially turkeys). The presence of DMZ and its metabolites in animal food poses potential risks to human health. In this study, we developed a high-performance liquid chromatography tandem mass spectrometry (HPLC/MS-MS) method for the precise detection of DMZ and its metabolite 2-hydroxymethyl-1-methyl-5-nitroimidazole (HMMNI). Our results demonstrate a strong linear relationship (r2 > 0.99) between the concentrations of DMZ and HMMNI in tissues and egg within the range of 1~100 ng/g. The limits of detection (LOD) were determined to be 0.5 ng/g, with corresponding limits of quantification (LOQ) at 1.0 ng/g. Furthermore, average recoveries in tissues and egg fell within the range of 84.90% to 103.01%, with coefficients of variation below 15% for both intra-day and inter-day analyses. To investigate the residue elimination pattern of DMZ and HMMNI, diets containing 500 mg/kg DMZ were fed to healthy SanHuang chicken and Hy-line Gray laying hens for 10 consecutive days. The results indicated that the concentration of HMMNI consistently exceeded that of DMZ during the same period, in both broiler tissues and egg. Sebum showed the slowest elimination of DMZ and HMMNI, becoming undetectable after 168 h of withdrawal. In egg, residues of both substances peaked on the first day after drug withdrawal, followed by slow elimination with half-lives of 0.45 days for DMZ and 0.66 days for HMMNI. Based on these findings, WT1.4 software was used to calculate a withdrawal time of 11 days for broilers and an egg abandonment period of 14 days after withdrawal for laying hens, providing a scientific basis for the safe and rational use of DMZ in poultry farming.

Pharmacokinetic/pharmacodynamic relationships of enrofloxacin against Klebsiella pneumoniae in an in vivo infection model in young chicks.

Klebsiella pneumoniae is a serious pathogenic bacterium that poses a significant threat to young poultry and the cause of significant chick mortality and economic loss. We investigated the therapeutic efficacy of enrofloxacin in treating K. pneumoniae infections in chicks and employed an in vivo pharmacokinetic/pharmacodynamic (PK/PD) model. In vivo efficacy was evaluated using 6 multiple-dose groups (oral administration once a day for 3 d) and 2 single-dose groups (oral administration once only). The PK and PD parameters of plasma and lung were analyzed using PK/PD fitting analysis. K. pneumoniae administered intratracheally (108 CFU/mL in 0.4 mL saline) was used to establish a model for pulmonary infection. The plasma protein binding of enrofloxacin was 20.18%. Enrofloxacin displayed T1/2ß values of 4.78 ± 0.69 h and 4.78 ± 1.02 h in plasma and lung of infected chicks, respectively. When the dosage in the multiple-dose group was > 10 mg/kg, bactericidal activity was found and complete eradication was not achieved when the dosage was ≤ 40 mg/kg. When TMSW was set at 20%, the calculated dosage and bacterial reduction (E) based on plasma free drug data were 4.03 mg/kg and -1.982 Log10 CFU/mL, respectively. In the calculation of PK/PD parameters for reducing 3 Log10 CFU/mL and using Cmax/MIC, AUC72h/MIC and TMSW of free drug in plasma values at 9.479, 379.691, and 44.395%, respectively, the value of AUC72h/MIC based on the concentration of drug in lung was 530.800. According to the fitting correlation R2, the PK/PD fitting results of free drug in plasma were better. The corresponding enrofloxacin dosage for AUC72h/MIC of the plasma free drug concentration was 14.16 mg/kg. The administration regimen corresponding to these dosages was once daily for 3 d. This dosage regimen (14.16 mg/kg) was relatively high compared to the clinically recommended dosage in China (7.5 mg/kg) when treating infections caused by K. pneumoniae with MIC ≥ 0.125 µg/mL, so careful consideration is needed.

Lung microdialysis and in vivo PK/PD integration of cefquinome against Actinobacillus pleuropneumoniae in a porcine experimental lung infection model.

This study aim to explore the application of microdialysis in pharmacokinetic (PK) and pharmacodynamic (PD) integration of cefquinome against Actinobacillus pleuropneumoniae in a porcine experimental lung infection model. The model was established via intratracheal inoculation where average bacterial counts (CFU) in the lungs of infected pigs reached 6.57 log10 CFU/g after 3 h. The PK profiles of unbound cefquinome in lung dialysates were determined following intramuscular injection of single doses of 0.125, 0.25, 0.5, 1, 2, and 4 mg/kg. Lung dialysate samples were collected using microdialysis at a flow rate of 1.5 µL/min until 24 h. The PD studies were conducted over 24 h based on 10 intermittent dosing regimens and total daily doses ranged from 0.25 to 4 mg/kg and dosage intervals included 12 and 24 h. The lung tissue was collected after 24 h of treatment and homogenized for bacterial counts. The relationships between PK/PD parameters derived from lung dialysates and drug efficacy were analyzed using an inhibitory sigmoid Emax model. The percentage of time the free drug concentration exceeded the minimum inhibitory concentration (%fT > MIC) was the PK/PD index best describing the antimicrobial activity (R2 = 0.96) in the porcine experimental infection model. The %fT > MIC values required to achieve net bacterial stasis, 1, 2 and 3 log10 CFU/g reductions in the lung were 22.45, 28.86, 37.62, and 56.46%, respectively. Cefquinome exhibited time-dependent characteristics against A. pleuropneumoniae in vivo. These results provide valuable insights into the application of microdialysis in PK/PD integration model studies and optima regimen of cefquinome for the treatment of porcine respiratory diseases caused by A. pleuropneumoniae.

Chlorogenic acid attenuates tet (X)-mediated doxycycline resistance of Riemerella anatipestifer.

Introduction: The increasing resistance of R. anatipestifer has posed a significant threat to the poultry industry in recent years. The tet gene is the primary determinant of tetracycline resistance in numerous bacteria, and the enzyme modification gene tet(X) is predominantly detected in tetracycline-resistant R. anatipestifer strains. Methods: In this study, we evaluated the susceptibility of both the standard strain and clinical isolates of R. anatipestifer to doxycycline. And the expression levels of tet(X), tet(A), and tet(O) genes were detected. To assess drug susceptibility, shuttle plasmids were constructed to transfer the tet(X) gene into the standard strain of R. anatipestifer followed by treatment with chlorogenic acid. Results and discussion: The results revealed that the minimum inhibitory concentration of doxycycline for the standard strain was 0.25µg/mL, whereas it exceeded 8µg/mL for the clinical isolates. Furthermore, there was a significant upregulation observed in expression levels of tet(X), tet(A), and tet(O) genes among induced strains. Interestingly, when transferring the tet(X) gene into the standard strain, its sensitivity to doxycycline decreased; however, MIC values for chlorogenic acid remained consistent between both standard and drug-resistant strains of R. anatipestifer. Moreover, we made a surprising discovery that screening passage with chlorogenic acid resulted in increased sensitivity of R. anatipestifer to doxycycline. Further analysis demonstrated a reversal in expression trends among three differentially expressed genes within induced drug resistance group after intervention with chlorogenic acid. The main objective behind this study is to investigate both killing effect exerted by chlorogenic acid on drug-resistant R. anatipestifer as well as its regulatory impact on drug resistance genes. This will provide novel insights and theoretical basis towards development of chlorogenic acid as a promising drug for treatment and control of drug resistance in R. anatipestifer.