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

Unravelling Antimicrobial Resistance in Mycoplasma hyopneumoniae: Genetic Mechanisms and Future Directions

Antimicrobial resistance (AMR) in Mycoplasma hyopneumoniae, the causative agent of Enzootic Pneumonia in swine, poses a significant challenge to the swine industry. This review focuses on the genetic foundations of AMR in M. hyopneumoniae, highlighting the complexity of resistance mechanisms, including mutations, horizontal gene transfer, and adaptive evolutionary processes. Techniques such as Whole Genome Sequencing (WGS) and multiple-locus variable number tandem repeats analysis (MLVA) have provided insights into the genetic diversity and resistance mechanisms of M. hyopneumoniae. The study underscores the role of selective pressures from antimicrobial use in driving genomic variations that enhance resistance. Additionally, bioinformatic tools utilizing machine learning algorithms, such as CARD and PATRIC, can predict resistance traits, with PATRIC predicting 7 to 12 AMR genes and CARD predicting 0 to 3 AMR genes in 24 whole genome sequences available on NCBI. The review advocates for a multidisciplinary approach integrating genomic, phenotypic, and bioinformatics data to combat AMR effectively. It also elaborates on the need for refining genotyping methods, enhancing resistance prediction accuracy, and developing standardized antimicrobial susceptibility testing procedures specific to M. hyopneumoniae as a fastidious microorganism. By leveraging contemporary genomic technologies and bioinformatics resources, the scientific community can better manage AMR in M. hyopneumoniae, ultimately safeguarding animal health and agricultural productivity. This comprehensive understanding of AMR mechanisms will be beneficial in the adaptation of more effective treatment and management strategies for Enzootic Pneumonia in swine.

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.

Differential domains and endoproteolytic processing in dominant surface proteins of unknown function from Mycoplasma hyopneumoniae and Mycoplasma flocculare

Mycoplasma hyopneumoniae causes porcine enzootic pneumonia (PEP), a chronic respiratory disease that leads to severe economic losses in the pig industry. Swine infection and PEP development depend on the adhesion of the pathogen to the swine respiratory tract and the host immune response, but these and other disease determinants are not fully understood. For instance, M. hyopneumoniae has a large repertoire of proteins of unknown function (PUFs) and some of them are abundant in the cell surface, where they likely mediate so far unknown pathogen-host interactions. Moreover, these surface PUFs may undergo endoproteolytic processing to generate larger repertoires of proteoforms to further complicate this scenario. Here, we investigated the five PUFs more represented on the surface of M. hyopneumoniae pathogenic strain 7448 in comparison with their orthologs from the nonpathogenic M. hyopneumoniae J strain and the closely related commensal species Mycoplasma flocculare. Comparative in silico analyses of deduced amino acid sequences and proteomic data identified differential domains, disordered regions and repeated motifs. We also provide evidence of differential endoproteolytic processing and antigenicity. Phylogenetic analyses were also performed with ortholog sequences, showing higher conservation of three of the assessed PUFs among Mycoplasma species related to respiratory diseases. Overall, our data point out to M. hyopneumoniae surface-dominant PUFs likely associated with pathogenicity.

Association between Tulathromycin Treatment for Bovine Respiratory Disease and Antimicrobial Resistance Profiles among Gut Commensals and Foodborne Bacterial Pathogens Isolated from Feces of Beef Steers

ABSTRACT

This study was conducted to evaluate the association between a therapeutic dose of tulathromycin for bovine respiratory disease in beef steers and the antimicrobial and multidrug resistance profiles of the gastrointestinal tract commensals Escherichia coli and Enterococcus spp. and the foodborne pathogens Salmonella enterica and Campylobacter spp. isolated from fecal samples. Individual fecal samples were collected on days 0, 14, and 28 from 70 beef steers that were housed in a single pen and had been treated or not treated with tulathromycin. Samples were cultured for bacterial isolation, and isolates were tested for antimicrobial susceptibility with the broth microdilution method to determine the MICs of clinically relevant antimicrobials used in both human and veterinary medicine. Generalized linear mixed effects models were fitted to estimate the prevalence of the bacterial species and the prevalence of resistant isolates over time and between treated and nontreated cattle and of multidrug-resistant isolates. Model-adjusted mean prevalences of E. coli, Enterococcus spp., S. enterica, and Campylobacter spp. were 99.5, 85.9, 1.5, and 17.7%, respectively. The prevalence of erythromycin-resistant Enterococcus spp. was significantly higher on day 14 (59.7%) than on day 28 (22.2%). A higher prevalence of erythromycin-resistant Enterococcus spp. was found in samples from treated (59.3%) than in samples from nontreated (27.6%) animals. Multidrug resistance (three or more antimicrobial classes) was observed in 8.4% of E. coli isolates and 62.7% of Enterococcus isolates. The administration of tulathromycin was significantly associated with an increased prevalence of erythromycin-resistant Enterococcus spp. isolates.

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