Pharmacokinetic-pharmacodynamic integration and resistance of tiamulin against Mycoplasma hyopneumoniae in an in vitro dynamic model

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.

PK-PD integration of enrofloxacin and cefquinome alone and in combination against Klebsiella pneumoniae using an in vitro dynamic model

Introduction: Klebsiella pneumoniae is classified as a critical pathogen in both animals and humans and infections can be fatal in chickens resulting in substantial economic losses. However, the misuse of antibiotics can also lead to drug resistance and a potential transmission chain between animals and humans. Three K. pneumoniae strains with different susceptibility phenotypes were chosen to study the pharmacokinetic/pharmacodynamic (PK/PD) integration of enrofloxacin (ENR) and cefquinome (CEQ) alone and in combination. Results: Checkerboard assay results indicated that the combination treatment for type strain ATCC 700603 was synergistic effect with a fractional inhibitory concentration index (FICI) of ≤0.5. The other two clinical strains demonstrated an additive effect (FICI >0.5 to ≤1). Furthermore, static time-kill curves indicated that enrofloxacin and cefquinome added singly were effective in killing K. pneumoniae at concentrations of >2 MIC and ≥1 MIC, respectively. Additionally, the combination of enrofloxacin and cefquinome led to an enhanced antibacterial activity of cefquinome. The dynamic time-kill curves indicated that enrofloxacin and cefquinome had bactericidal and bacteriostatic activities, respectively at ≥1.5 mg/L (single-dose) and 4 mg/L (8 h split-dose) causing a decrease in bacterial counts of ≥4.45 and >2 log10 CFU/mL. Enrofloxacin possessed no bacteriostatic effects against K. pneumoniae at a constant concentration of 1× MIC. Cefquinome used in combination with 1× MIC enrofloxacin exhibited bactericidal activity at ≥4 mg/L (12 h split-dose) with reductions of ≥3.65 log10 CFU/mL. The PK/PD parameters were also analyzed to determine the concentration and duration of the drugs needed to reduce bacteria by 3 log10 CFU/mL. For enrofloxacin alone, the AUC24h/MIC was 23.29 h and the Cmax/MIC was 3.18. For cefquinome alone, the %T > MIC was 48.66 and when used in combination with enrofloxacin was 18.04. The combined use of cefquinome and enrofloxacin can increase the antibacterial activity of cefquinome against K. pneumoniae under a 12-h split-dose regimen regardless of individual drug susceptibility. Discussion: The static and dynamic time-kill curves indicated that enrofloxacin exhibited concentration-dependent activity, while cefquinome exhibited time-dependent activity. In the in vitro dynamic model, enrofloxacin alone exhibited better antimicrobial effects against K. pneumoniae compared to cefquinome alone. However, the antibacterial effect of cefquinome can be enhanced by combining it with enrofloxacin. These findings suggest a potentially effective approach for combating K. pneumoniae infections.

Emergence and Mechanism of Resistance of Tulathromycin Against Mycoplasma hyopneumoniae in a PK/PD Model and the Fitness Costs of 23S rRNA Mutants

Macrolides are widely used in diseases caused by Mycoplasma spp. The new semi-synthetic macrolide antibiotic tulathromycin is currently in wide use for the treatment of respiratory diseases of livestock. The objective of this study was to evaluate the antibacterial effect of tulathromycin against Mycoplasma hyopneumoniae using an in vitro pharmacokinetic/pharmacodynamic (PK/PD) model to reveal mechanisms of antibiotic resistance and to evaluate the fitness of drug-resistant strains. In this study, high performance liquid chromatography-tandem mass spectrometry was used to determine drug concentrations for the in vitro model after dosing. The peak concentrations were in the range 0.3125–20 μg/mL (1 × MIC-64 × MIC). The ratio of the area under the concentration-time curve (AUC) over 72 h divided by the MIC (AUC_72h/MIC) had the highest correlation with the antibacterial effect of tulathromycin against M. hyopneumoniae. Tulathromycin also showed concentration-dependent antimicrobial effects and promoted the emergence of drug-resistant bacteria after being cultured for 168 h and most were mutations in 23S rRNA at site A2058G (E.coli numbering) and only a single isolate was an A2058T (E.coli numbering) mutant. In the presence of reserpine, we determined the MIC of tulathromycin, tilmicosin, tiamulin and tylosin against these drug-resistant bacteria and the strains with efflux pump mechanisms were found among the strains resistant to tilmicosin. Gene expression analysis indicated that the ABC and MATE transporter efflux pump genes RS01935, RS02670, RS01115, RS01970, RS02395 and RS03540 (MATE family efflux transporter) were up-regulated in the three strains (P < 0.05 or P < 0.01). These investigations provide guidance for clinical administration of tulathromycin and elucidate the mechanism and fitness cost of drug resistance in M. hyopneumoniae.

A novel electrochemical immunosensor for the sensitive detection of tiamulin based on staphylococcal protein A and silver nanoparticle-graphene oxide nanocomposites

Tiamulin (TML) is a pleuromutilin antibiotic and mainly used to treat pulmonary and gastrointestinal infections. However, excessive use of TML can bring health threats to consumers. In this work, a label-free electrochemical immunosensor was proposed for sensitive detection of TML in pork and pork liver. Silver nanoparticles (AgNPs) were synthesized in situ on graphene oxide (GO), in which GO acted as a carrier for loading more AgNPs and AgNPs exhibited both strong conductivity and good redox property. In addition, staphylococcal protein A (SPA) was applied to oriented immobilization of fragment crystallizable (Fc) region of the TML monoclonal antibody. Under the optimal condition, the developed electrochemical immunosensor exhibited a good linear response with a concentration of TML ranging from 0.05 ng mL^-1 to 100 ng mL^-1 and the limit of detection (LOD) was 0.04 ng mL^-1. Furthermore, the designed immunosensor was applied to detect TML in real samples with a good accuracy. Therefore, the label-free electrochemical immunosensor could be used as a potential method to detect TML and other antibiotic residues in animal derived foods.

Pharmacokinetics, bioavailability, and tissue disposal profiles of Tiamulin fumarate in Nile tilapia (Oreochromis niloticus) following oral and intravenous administrations

Tiamulin fumarate (TIF) is a pleuromutilin antibiotic and has high activity against animal bacterial pathogens including aquatic bacterial pathogens. However, its pharmacokinetic profiles, tissue distribution characteristics and bioavailability in aquatic animals remain unknown. The objective of this study was to investigate the pharmacokinetics and tissue distribution regularities of TIF in tilapia (Oreochromis niloticus) following a single oral (PO) dose of 20 mg/kg body weight (bw) and a single intravenous (IV) dose of 5 mg/kg bw at 22 ± 1°C, respectively. TIF concentrations in tilapia plasma and tissues were determined using the isotope dilution HPLC-HESI-MS/MS procedure, which was validated according to the guidelines defined by US Food and Drug Administration. TIF was well distributed throughout the body compartments of tilapia judged by the apparent volume of distribution (V_d ) >1 L/kg (6.69 L/kg PO and 1.78 L/kg IV). TIF had a short mean residence time (MRT; 22.82 h PO and 14.61 h IV) and quick total body clearance (CL_b ) (0.62 L kg^-1  h^-1 PO and 0.60 L kg^-1  h^-1 IV). The total area under the curve (AUC_tot ) of plasma were 32.25 μg h^-1  ml^-1 (PO) and 8.30 μg h^-1  ml (IV), respectively, and the oral absolute bioavailability (F%) of TIF was calculated to be approximately 97.1%. For tissue distribution, high concentrations of TIF were found in kidney, and the longest MRT was recorded in bile. The withdrawal time (WT) of TIF in muscle, skin, liver, kidney, gill, and bile was 3.75 (4) and 1.79 (2), 1.77 (2) and 2.06 (3), 6.41 (7) and 1.97 (2), 6.95 (7) and 3.98 (4), 4.92 (5) and 2.36 (3), and 7.06 (8) and 6.16 (7) days after PO and IV administration, respectively. The present investigations indicated that TIF was quickly absorbed, well distributed, rapidly eliminated in tilapia, and it could serve as reference data for establishing use regimen and provide useful information for the further development of TIF in aquaculture.