Highlight on the synergistic effect of different microemulsion formulations on the virulence determinants of multi-resistant Mycoplasma gallisepticum recovered from poultry.

This study is aimed at evaluating the efficacy of essential oil-based microemulsions in combination with antimicrobials against Mycoplasma gallisepticum (MG), a major respiratory pathogen in poultry. MG was isolated from 1.1% of broiler and 0.5% of breeder flocks, with the highest incidence recorded during winter and autumn, particularly in farms located in Giza and Sharkia governorates. Among 37 confirmed isolates, eight were positive for the mgc2 gene, while six carried gapA and crmA. Cumin, camphor, and olive microemulsions exhibited favorable physicochemical characteristics. GC-MS analysis identified α-citral, ( +)-2-bornanone, and cis-vaccenic acid as the major components of cumin, camphor, and olive oils, respectively. Notably, olive/camphor and cumin microemulsions were rich in cis-vaccenic acid and linoleoyl chloride, respectively. Antibiotic susceptibility testing revealed that all isolates were resistant to lincomycin, erythromycin, spectinomycin, and tiamulin, with 50% exhibiting complete resistance to all antibiotics. Tylosin showed partial activity, inhibiting 37.5% of isolates (MIC 0.25-4 µg/mL). Camphor microemulsion demonstrated the highest antimicrobial effect (MIC 0.08-5 µg/mL). The most significant synergistic interaction was observed between cumin oil and either oxytetracycline or spiramycin, as well as between camphor microemulsion and doxycycline against MG isolates. Furthermore, combination treatments significantly downregulated the expression of mgc2, crmA, and gapA genes. These findings highlight the promising role of essential oil-based microemulsions as effective adjuncts in MG control strategies.