Whole genome comparisons of Staphylococcus agnetis isolates from cattle and chickens

We report the comparisons of genomes of eleven isolates of Staphylococcus agnetis obtained from dairy cattle and chickens.

S. agnetis has been previously associated with subclinical or clinically mild cases of mastitis in dairy cattle and is one of several Staphylococcal species isolated from the bone and blood of lame broilers. We have previously shown that a chicken isolate 908 can induce bacterial chondronecrosis with osteomyelitis (BCO) in chickens with incidences of lameness over 50%. We have also assembled and analyzed the genome of isolate 908.

To better understand the relationship between dairy cattle and broiler isolates, we assembled genomes for S. agnetis isolated from an additional chicken BCO case, and from milk, mammary gland secretions or udder skin from the collection at the University of Missouri. To trace phylogenetic relationships, we constructed phylogenetic trees based on multi-locus sequence typing, and Genome-to-Genome Distance Comparisons.

Chicken isolate 908 clustered with two of the cattle isolates along with isolates from chickens in Denmark and an isolate of S. agnetis we isolated from a BCO lesion on a commercial farm in Arkansas. We used a number of BLAST tools to compare the chicken isolates to those from cattle and identified 98 coding sequences distinguishing isolate 908 from the cattle isolates. None of the identified genes explain the differences in host or tissue tropism.

These analyses are critical to understanding how Staphylococci colonize and infect different hosts and potentially how they can transition to alternative niches (bone vs dermis).