Abstract
Streptococcus uberis is one of the most frequent mastitis-causing pathogens isolated from dairy cows. Further understanding of S. uberis genetics may help elucidate the disease pathogenesis. We compared the genomes of S. uberis isolates cultured from dairy cows located in distinctly different geographic regions of Australia. All isolates had novel multi locus sequence types (MLST) indicating a highly diverse population of S. uberis. Global clonal complexes (GCC) were more conserved. GCC ST86 and GCC ST143 represented 30% of the total isolates (n = 27) and were clustered within different geographic regions. Core genome phylogeny revealed low phylogenetic clustering by region, isolation source, and MLST. Identification of putative sortase (srtA) substrates and generation of a custom putative virulence factor database revealed genes which may explain the affinity of S. uberis for mammary tissue, evasion of antimicrobial efforts and disease pathogenesis. Of 27 isolates, four contained antibiotic resistance genes including an antimicrobial resistance cluster containing mel/mef(A), mrsE, vatD, lnuD, and transposon-mediated lnuC was also identified. These are novel genes for S. uberis, which suggests interspecies lateral gene transfer. The presence of resistance genes across the two geographic regions tested within one country supports the need for a careful, tailored, implementation and monitoring of antimicrobial stewardship.
Highlights
Streptococcus uberis is one of the most frequent mastitis-causing pathogens isolated from dairy cows
A secondary objective was to examine the diversity of the isolates, in particular their specific antimicrobial resistance profiles from these different regions to identify geographic or climatic associations that may exist as a potential basis for development of more effective and sustainable mastitis treatments for dairy cows
All Global clonal complexes (GCC) ST86 isolates were from herds with high bulk milk somatic cell counts (270–400 × 103 cells/mL)
Summary
Streptococcus uberis is one of the most frequent mastitis-causing pathogens isolated from dairy cows. Variations in genetic profile among S. uberis strains were observed in isolates originating from different dairy herds, and in the pathogens present within the same h erd[7, 21] This inherently high genetic diversity renders the attribution of a specific set of virulence factors (and associated pathogenesis) to a given S. uberis strain/s challenging[12, 22, 23]. The main objectives of this study were to compare S. uberis isolates cultured from dairy cows with clinical mastitis in distinctly different geographic and climatic regions of Australia. A secondary objective was to examine the diversity of the isolates, in particular their specific antimicrobial resistance profiles from these different regions to identify geographic or climatic associations that may exist as a potential basis for development of more effective and sustainable mastitis treatments for dairy cows
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