Phylogenomic Comparison of Staphylococcus agnetis Isolates from Dairy Cattle Mammary Glands and Bacterial Chondronecrosis with Osteomyelitis in Broilers

Staphylococcus agnetis is a coagulase-variable, Gram positive bacterial species which has been previously associated with subclinical or mild clinical cases of mastitis in dairy cattle. This staphylococcal species has been isolated from the bone and blood of lame broilers at the University of Arkansas. Bacterial chondronecrosis with osteomyelitis (BCO) has also been successfully induced by administration of a chicken isolate of S. agnetis (strain 908) in drinking water. BCO primarily affects the growth plate in the proximal femur and tibia, the fast growing leg bones. When birds are reared on suspended wire flooring with administration of strain 908 in the drinking water (10E5 CFU/ml on days 20 and 21) lameness incidence is as high as 80% by 56 days of age. The same administration protocol induces lameness of 50% for birds raised on litter. The annotated complete genome of strain 908 has been published. To better understand the relationship between dairy cattle and broiler isolates, we obtained nine S. agnetis isolated from milk or mammary gland secretions (n = 7) and udder skin (n = 2) from the University of Missouri for sequencing (2 x 250 MiSeq) and de novo assembly (NGen ver 13, DNAStar). To trace phylogenetic relationships, we constructed phylogenetic trees based on multi locus sequence typing using either 7 housekeeping genes or 7 virulence genes. Included in this analysis were published genomes from NCBI for S. agnetis and the closely related species Staphylococcus hyicus as outgroup. The chicken isolate, strain 908, clustered with two of the cattle isolates. A catalogue of gene differences between the cattle and chicken isolates is being constructed using reciprocal blast analyses at the nucleotide and polypeptide level. More than 40 genes from strain 908 are absent or poorly conserved in any of the cattle S. agnetis isolates. Work is underway on annotation and pathway analysis of these genes.