Diversity of spp. and genomic characteristics of isolated from clinical mastitis of cattle in Bangladesh.

INTRODUCTION

Streptococci are the major etiology in mastitis in dairy cattle, a cause of huge economic losses in the dairy industries. This study was aimed to determine the diversity of spp. isolated from clinical mastitis of cattle reared in Bangladesh.

METHODS

A total of 843 lactating cattle reared in four prominent dairy farms and one dairy community were purposively included in this study where 80 cattle were positive to clinical mastitis (CM) based on gross changes in the udder (redness, swelling, and sensitive udder) and/or milk (flakes and/or clots). Milk samples were collected from all the eighty cattle with clinical mastitis (CCM) and twenty five apparently healthy cattle (AHC). Samples were enriched in Luria Bertani broth (LB) and one hundred microliter of the enrichment culture was spread onto selective media for the isolation of spp., spp., spp., and spp., the major pathogen associated with mastitis. Isolates recovered from culture were further confirmed by species specific PCR.

RESULTS AND DISCUSSION

Out of 105 samples examined 56.2% (59/105), 17.14% (18/105), 9.52% (10/105) and 22.9% (24/105) samples were positive for , , and , respectively. This study was then directed to the determination of diversity of spp. through the sequencing of . A total of eighteen of the samples from CCM (22.5%) but none from the AHC were positive for spp. by cultural and molecular examination. Sequencing and phylogenetic analysis of identified 55.6, 33.3, 5.6 and 5.6% of the isolates as , , and , respectively. Considering the high prevalence and worldwide increasing trend of in mastitis, in-depth molecular characterization of was performed through whole genome sequencing. Five of the strain isolated in this study were subjected to WGS and on analysis two novel ST types of were identified, indicating the presence of at least two different genotypes of in the study areas. On virulence profiling, all the isolates harbored at least 35 virulence and putative virulence genes probably associated with intramammary infection (IMI) indicating all the isolated in this study are potential mastitis pathogen. Overall findings suggest that encountered in bovine mastitis is diverse and might be predominantly associated with CM in the study areas. The genome carries an array of putative virulence factors that need to be investigated genotypically and phenotypically to identify a specific trait governing the virulence and fitness of this bacterium. Moreover, the genomic information could be used for the development of new genomic tools for virulence gene profiling of .