Comparative Lung Bacterial Community Profiles in Pneumonic and Non-Pneumonic Akkaraman Lambs

Ovine pneumonia is a multifactorial respiratory disease, yet bacterial community alterations associated with pathologically confirmed pneumonia in lambs remain poorly characterised. This study investigated the lung bacterial microbiota of non-pneumonic and pneumonic Akkaraman lambs by integrating gross and histopathological examination with 16S rRNA gene amplicon sequencing. The final dataset comprised lung samples from 15 non-pneumonic and 14 pneumonic lambs. Alpha diversity did not differ significantly between groups, whereas bacterial community composition differed significantly for both Bray-Curtis (R² = 0.093, p = 0.001) and weighted UniFrac (R² = 0.117, p = 0.006) distances, with no significant differences in multivariate dispersion. At the genus level, Mannheimia showed significantly higher relative abundance in pneumonic lungs after false-discovery-rate correction and was the only genus also identified as differentially abundant by ANCOM. Mycoplasma, Fusobacterium, and Trueperella showed greater relative representation in pneumonic lungs, whereas Acinetobacter and Psychrobacter showed the opposite pattern. Prevalence analysis further demonstrated contrasting taxon distributions between groups. Overall, naturally occurring pneumonia was associated with distinct alterations in lung bacterial community composition rather than a generalised loss of within-sample diversity, with Mannheimia representing the strongest pneumonia-associated genus-level signal.