Prevalence and population biology of mastitis-causing Streptococcus uberis using an MLST based approach

Streptococcus uberis is a predominant causative agent of both clinical and subclinical varieties of bovine mastitis, an economically significant infection affecting dairy industries around the world. Yet, the genetic and evolutionary relationships among S. uberis strains from different countries are poorly understood. In this study, we used S. uberis's multilocus sequence typing (MLST) method of genotyping to decipher country-wise prevalence of sequence types (STs) and ST complexes and to delineate genetic relationships among them. Dataset collected from PubMLST database for S. uberis was subjected to clonal cluster and phylogenetic analyses using BURST, globally optimized eBURST (goeBURST) and neighborhood joining algorithm tools, respectively. Whereas certain countries showed clear trends of strain prevalence, others had a more equally weighted, diverse population. Occurrence of different severities of disease varied among countries and displayed no direct correlation with ST. Clonal cluster and phylogenetic analyses predicted the ancestral roles of certain prominent STs and indicated possible strain migration and reticulate and convergent evolution occurring within the S. uberis population at a global scale. Furthermore, genome comparison of selected strains revealed the absence of SUB0822-SUB0826 response regulator proteins from ST-5 and ST-6 indicating their preference for contagious transmission. Information generated from this study would be crucial for monitoring infection outbreaks and directing further genomic investigations.