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

Abstract

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 (AUC72h/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.

Assessing the Emergence of Resistance in vitro and Invivo: Linezolid Combined with Fosfomycin Against Fosfomycin-Sensitive and Resistant Enterococcus

“…The high resistance to fosfomycin suggests that the dose of the drug needs to be strictly controlled clinically. 32 Recent studies on vancomycin in the treatment of enterococcal infection revealed that parameters such as AUC/MIC and valley concentration can guide the concentration control of vancomycin, thereby improving treatment results and reducing side effects such as nephrotoxicity. 71 , 72 This suggests that we need to conduct in-depth studies of relevant PK/PD models to identify drug-related therapies and resistance targets to optimize the clinical choice of individualized doses.…”

“…Where RF is the number of resistant bacteria at the end of culture, RI is the number of resistant bacteria before culture, SF is the number of susceptible bacteria at the end of culture, and SI is the number of susceptible bacteria before culture. W < 1 indicates that the competitive fitness of S is better than that of R, W = 1 indicates that the competitive fitness of S and R is similar, and W > 1 indicates that the competitive fitness of R is better than that of S. 32 …”

“…Where RF is the number of resistant bacteria at the end of culture, RI is the number of resistant bacteria before culture, SF is the number of susceptible bacteria at the end of culture, and SI is the number of susceptible bacteria before culture. W < 1 indicates that the competitive fitness of S is better than that of R, W = 1 indicates that the competitive fitness of S and R is similar, and W > 1 indicates that the competitive fitness of R is better than that of S. 32 To further study the competition between the mutant and parent body, the same volume of NO.22 and NO.22R suspensions was adjusted with PBS to a bacterial concentration with lethality of 80% and injected into the larvae. The hemolymph was collected at the same time point as in vitro, and the hemolymph was uniformly spread on a common agar plate and an agar plate containing 1 × MIC fosfomycin and incubated at 37 °C for 24 h. A colony count was performed to calculate the load of hemolymph fluid in each node.…”

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

“…According to previous reports ( 21 – 23 ), an in vitro model compatible with M. gallisepticum growth and amphenmulin pharmacokinetics was developed ( 24 ). It comprised a reservoir chamber containing fresh, drug-free medium; a reaction chamber with a three-necked flask where amphenmulin interacts with M. gallisepticum , containing 300 mL of medium in the outer chamber (external compartment, EC) and 10 mL of M. gallisepticum culture (10 7 CFU/mL) in a semipermeable membrane chamber (internal compartment, IC); and a waste chamber collecting effluent, which were connected via tubing and controlled by a peristaltic pump ( Fig.…”