Virulence associated genes in Streptococcus uberis

Infection caused by bacteria from environmental reservoirs such as E. coli and S. uberis have not decreased in prevalence. Lack of success in controlling bovine mastitis due to S. uberis is associated with the route of infection which is not well understood and there is inadequate information on pathogenesis of S. uberis. Therefore, this study was to investigate the virulence factors of S. uberis using comparative genome analyses using isolates from cows with clinical mastitis and isolates from cows with a low cell count in their milk using a Subtracted Diversity Array (SDA). This study also reports the construction and validation of a microarray capable of fingerprinting the virulent and non-virulent isolates using the SDA technique. DNA of 29 non-virulent strains and virulent strains was subtracted from pooled genomic DNA of 12 S. uberis strains. 280 subtracted DNA fragments were used to construct S. uberis-specific array. The validation of S. uberis-specific array revealed a high (77%) subtraction efficiency. 29 S. uberis strains, representing 20 clinical isolates and 9 low cell counts were hybridized onto the array to reveal its level of strain discrimination based on the prevalence and virulence specificity for each S. uberis tested strain. All these species could be successfully differentiated using their hybridization patterns. 26 probes were characterized by sequencing. A number of probes were novel virulence associated gene whilst some of them could indicate their essential roles as virulence factors.