Impairment in the Isolation of Mycoplasma synoviae in Mixed Infection with Mycoplasma gallinaceum in Laying Hens

Avian mycoplasmosis is a disease of significant economic impact, potentially leading to restrictions on the international trade of poultry products. Mycoplasma synoviae (MS) and Mycoplasma gallisepticum (MG) are well-established as pathogenic, while Mycoplasma gallinaceum (Mgc) is considered commensal. Nevertheless, the latter can exacerbate clinical conditions in cases of co-infections with other pathogens. Due to the slow growth rates of MS and MG, they are susceptible to being outpaced by fast growing mycoplasmas, thereby complicating cultivation, and potentially yielding false-negative results. Thus, this study aimed to report a mixed infection of Mgc and MS in commercial laying hens and the compromised isolation of MS caused by this nonpathogenic mycoplasma. Twenty tracheal samples from chickens were collected, subjected to PCR, and cultured in a modified Frey's medium. Samples displaying colonies compatible with mycoplasmas underwent three passages to obtain pure cultures. PCR-positive samples for the Mycoplasma spp., and negative ones for MS and MG, were subsequently subjected to DNA sequencing. All clinical samples tested via PCR were positive for MS (20/20) and negative for MG (0/20). During isolation, only five samples exhibited colonies with characteristic mycoplasma growth. However, PCR analysis of these cultures produced negative results for MS and MG, but were positive for Mycoplasma spp. DNA sequencing confirmed that all isolated strains were Mgc. Mgc displayed rapid growth, posing challenges to obtaining MS strains for isolation. The coexistence of MS and Mgc in the respiratory tract of commercial laying hens has the potential of inducing a synergistic effect on respiratory manifestations.