The pulmonary system of birds is a considered a reservoir of innumerable bacterial pathogens including those which are subject to public health significance. This scenario makes respiratory tract of birds prone to many bacterial infections as well. There are many respiratory outbreaks in poultry that causes huge economic losses and a number of bacterial pathogens either acting as primary or secondary pathogen can be held responsible for these losses. A very small fraction of (<1%) of bacterial species are culturable, limited as well as highly variable and time consuming conventional microbiological procedures have typically excluded the normal flora present in the respiratory tract or have restricted the analysis to potential pulmonary pathogens. Due to unculturable nature of many bacterial species there is a very little room left for discovering or determining novel organisms or pathogens and their association with clinical outcomes through conventional microbiological procedures. With the advancement of technology metagenomic analysis of a given sample has emerged as a major culture independent technique for identification of many pathogens, by reading the hypervariable region of the 16S rRNA gene, culture-independent technique such as 454-pyrosequencing, can provide species specific sequence of any bacteria in a given sample.
A total of 12 T-BAL samples from breeder birds were selected based upon the quality and quantity of the double-stranded gDNA. Using 454 bar-coded pyrosequencing, the hypervariable regions of the 16S rRNA gene corresponding to V1 – V5 (~ 1,000 bp) were sequenced. Of the high-quality reads obtained (296,811) using the MOTHUR platform, the sequences were processed for sequence alignment with the 16S RDP database via BLASTn, and subsequent taxonomic analysis through MEGAN programs using a homology-based method to bin sequence reads. The results of study indicate that birds harbor a diverse microbial community including number of phyla, families, genera and characterized bacterial species. The bacterial communities were relatively conserved at the phylum level; however, at lower taxonomic levels, differences were observed in the phylotypes and abundance between the clinically diseased and healthy birds. As indicated by the rarefaction plot and the Shannon-Wiener and Simpson-Reciprocal diversity indices, the biodiversity and richness in the taxonomic content was higher in the clinically healthy birds compared with the diseased birds. Regardless of the bird health status a number of new species were identified. A number of these bacterial species have been found to be associated with infectious diseases in humans and other species, although the clinical importance of these bacteria as part of the respiratory microbiome of birds has not been established.
As the nature of bacterial species is to constantly act with one another and, potentially, with the birds themselves provides an interesting avenue for continued research. There is a need to conduct further clinico-pathological studies to establish the link between causes versus effects.