New Insights into the Host–Pathogen Interaction of Mycoplasma gallisepticum and Avian Metapneumovirus in Tracheal Organ Cultures of Chicken

Abstract

Respiratory pathogens are a health threat for poultry. Co-infections lead to the exacerbation of clinical symptoms and lesions. Mycoplasma gallisepticum (M. gallispeticum) and Avian Metapneumovirus (AMPV) are two avian respiratory pathogens that co-circulate worldwide. The knowledge about the host–pathogen interaction of M. gallispeticum and AMPV in the chicken respiratory tract is limited. We aimed to investigate how co-infections affect the pathogenesis of the respiratory disease and whether the order of invading pathogens leads to changes in host–pathogen interaction. We used chicken tracheal organ cultures (TOC) to investigate pathogen invasion and replication, lesion development, and selected innate immune responses, such as interferon (IFN) α, inducible nitric oxide synthase (iNOS) and IFNλ mRNA expression levels. We performed mono-inoculations (AMPV or M. gallispeticum) or dual-inoculations in two orders with a 24-h interval between the first and second pathogen. Dual-inoculations compared to mono-inoculations resulted in more severe host reactions. Pre-infection with AMPV followed by M. gallispeticum resulted in prolonged viral replication, more significant innate immune responses, and lesions (p < 0.05). AMPV as the secondary pathogen impaired the bacterial attachment process. Consequently, the M. gallispeticum replication was delayed, the innate immune response was less pronounced, and lesions appeared later. Our results suggest a competing process in co-infections and offer new insights in disease processes.

Mycoplasmas as Host Pantropic and Specific Pathogens: Clinical Implications, Gene Transfer, Virulence Factors, and Future Perspectives

“…It undertakes the invasion through penetration. Eventually, it resides intracellular, causing chronic or latent infection (Rüger et al, 2021).…”

“…Generally, after the invasion, mycoplasmas evolve and adapt to their parasitic intracellular life, they have slow intracellular growth rates compared to other extracellular bacteria. Their slow intracellular growth rate is mainly allowing them to hide and evade the host immune system (Rüger et al, 2021).…”

The expression of GapA and CrmA correlates with the Mycoplasma gallisepticum in vitro infection process in chicken TOCs

“…To determine the colonisation pattern of M. gallisepticum in TOCs, the bacterial antigen (Ag) was stained. The tissue sections were prepared from formalin-fixed TOCs and staining procedure was conducted as described on our previous study [ 30 ]. Primary antibodies (Abs) (polyclonal rabbit anti -MG [ 31 ], diluted 1:1000) were added and incubated overnight in a humid chamber at 4 °C.…”

“…TOCs were visually divided into ten equal sections, equivalent to 10% of ciliary activity per section. The average ciliary activity of ten tracheal rings / time point / group was calculated, as described in our previous study [ 30 ].…”

“…Chickens exposed to the pathogenic M. gallisepticum strain Ap3AS showed disintegrated epithelium, loss of cilia, and reduced intraepithelial mucous glands in the trachea [ 29 ]. In our previous study, histopathological examinations of tracheal organ cultures (TOC) confirmed the initiation of ciliary dysfunction after infection with the pathogenic M. gallisepticum strain S6 [ 30 ].…”