Advancing standardization of diagnostics and antimicrobial susceptibility testing for pathogenic mycoplasmas of livestock origin: insights from the MyMIC network.

Background
Mycoplasma infections pose a significant economic burden and represent a serious health and welfare concern for the livestock sector. Their control often requires repeated antimicrobial treatments. Antimicrobial susceptibility testing (AST) procedures for veterinary mycoplasmas lack standardization. Furthermore, clinical breakpoints (CBPs) are not available to interpret AST data (i.e., Minimum Inhibitory Concentration, MIC values) and categorize isolates as susceptible, resistant, or intermediate to the different antimicrobials used in livestock, nor epidemiological cut-offs (ECOFFs), which are a prerequisite to define CBPs. In 2023, the MyMIC network - a consortium of 22 laboratories specializing in veterinary mycoplasmas- was established to support efforts in standardizing diagnostics and AST, including clinical interpretation. Its initial goals were to (i) review routine diagnostic practices in frontline laboratories and examine veterinarians' prescribing habits and (ii) assess practices for culture, identification and AST used in expert laboratories and how these practices may affect MIC results as collected for five major livestock pathogens (M. bovis, M. gallisepticum, M. synoviae, M. hyopneumoniae and M. hyorhinis).Results
A first survey targeting veterinarians from the avian, porcine, and ruminant livestock sectors provided 468 complete responses from 39 countries worldwide, giving an account of current trends in the treatment and first-line diagnosis of veterinary mycoplasmoses. Macrolides, tetracyclines, pleuromutilins, florfenicol and fluoroquinolones were the most frequently administered antimicrobials, with usage varying by livestock sector. Veterinarians reported requesting diagnostic in 40-75% of clinical cases, but only one-third requested AST regularly. A separate survey within the consortium highlighted significant variability in the media and methods used by specialized laboratories, particularly for MIC determination, which relied mostly on in-house broth dilution techniques. This methodological diversity limited our ability to aggregate collected MIC data for establishing ECOFFs.Conclusions
Several concerns regarding best practices for antimicrobial treatments of mycoplasma infections may be linked to the lack of AST in frontline laboratories. Based on information collected in expert laboratories, we identified multiple sources contributing to inconsistent MIC results. The next step will be to establish consensus gold-standard AST methods tailored to specific mycoplasma-antimicrobial combinations to generate reliable MIC data for defining ECOFFs. Subsequently, the development of ready-to-use commercial MIC plates for use in frontline laboratory will support veterinarians in selecting appropriate treatments.