Identification and characterization of novel small molecule inhibitors to control Mycoplasma gallisepticum infection in chickens

Mycoplasma gallisepticum (MG) causes chronic respiratory disease in chickens, leading to severe economic losses to the poultry industry. Currently the disease is managed with antimicrobials and vaccination; however, emergence of multi-drug resistant Mycoplasma and the limited effect of vaccines necessitate development of novel approaches. A library of 4,182 small molecules (SMs) was screened for identification of narrow spectrum anti-MG compounds using high throughput screening. A total of 584 SMs were identified. Ten SMs possessed low MICs (0.78–100 μM) with efficacy against multiple MG strains and MG biofilm. These 10 SMs did not affect commensal/probiotic bacteria and other avian and foodborne pathogens. They displayed no or little toxicity on the avian macrophage HD-11 cells, human epithelial Caco-2 cells, and chicken red blood cells (RBCs); but, they were effective in reducing MG in chicken RBCs. Six SMs (SM1, SM3−5, and SM9−10) were tested in three-week-old chickens infected with MG (nasal spray; 10⁹ CFU/bird). SM4 and SM9 reduced airsacculitis by 77.2 % and 82.9 %, MG load in the trachea by 0.9 log (p < 0.05) and 2.7 log (p < 0.0001), and tracheal mucosal thickness by 23 % and 61 %, respectively with no impact on the richness and evenness of the cecal (P = 0.6; H = 1.0) and tracheal (P = 0.8; H = 0.8) microbiota compared to the MG-infected controls. Both SM4 and SM9 treatments resulted in a significant alteration in the cell membrane conformation of MG. In conclusion; we identified two novel growth inhibitors of MG that are effective in chickens. These findings will facilitate development of novel antibacterials to control mycoplasmosis in poultry.