Genomic diversity ofStreptococcus uberisisolated from clinical mastitis of cattle in selected areas of Bangladesh

Abstract

ABSTRACTStreptococci are the major etiology in mastitis, a cause of huge economic losses in the dairy industries.Streptococcus(S.)agalactiae, S. dysagalactiaeandS. uberisare mostly encountered in bovine mastitis; however, data on the diversity and characteristics of Streptococcus in clinical mastitis of cattle in Bangladesh is lacking. Thus, the present study was aimed to determine the diversity and antimicrobial resistance pattern ofStreptococcusspp. isolated from clinical mastitis of cattle reared in Bangladesh. A total of 105 milk samples comprising eighty (80) from cattle with clinical mastitis (CCM) and twenty-five (25) from apparently healthy cattle (AHC) in four prominent dairy farms and one dairy community were purposively collected and examined in this study. Milk samples were enriched in Luria Bertani broth (LB) andStreptococcusspp. was isolated on Modified Edwards Medium and identified by 16S rRNA gene sequencing. Among eighty (80) clinical samples, eighteen (18) were positive forStreptococcusspp. while none of the milk from AHC revealed Streptococcus by cultural and molecular examination. Sequencing and phylogenetic analysis identified 55.6%, 33.3%, 5.6% and 5.6% of the Streptococcus isolates asS. uberis, S. agalactiae, S. hyovaginalisandS. urinalis, respectively. Antibiotic sensitivity testing with antimicrobials commonly used to treat clinical mastitis revealed 100%, 100%, and 30% of theS. agalactiae,S. hyovaginalis, andS. uberisas multidrug-resistant, respectively. Molecular characterization through whole genome sequencing of five (5)S. uberisisolates identified at least two novel ST types ofS. uberiscirculating in the study areas with one ST (4/5 isolates) clustered with the isolates from China, India and Thailand, and the other (1/5) with UK, Ireland and Australia. Pan-genome analysis and phylogeny of the core genome sequences also clustered the isolates into two sub-clusters, indicating the presence of at least two different subtypes ofS. uberisin the study area. On virulence profiling, all the isolates of this study were found to harbor at least 35 virulence and putative virulence genes probably associated with intramammary infection (IMI) indicating all theS. uberisisolated in this study as potential pathogen. From the overall findings it was evident that Strepococcus occurring in bovine mastitis are diverse andS. uberisgenome carries an array of putative virulence factors which need to be investigated genotypically and phenotypically to identify a specific trait or determinant governing the virulence and fitness of this bacterium. Moreover, Streptococcus isolated in this study carried multidrug resistance which needs careful consideration during the selection of a treatment regimen for mastitis.